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In this contribution, we employ a recurrent neural network (RNN) architecture in a variational optimization to obtain the ground state of linear chains of planar, dipolar rotors. We test different local basis sets and discuss their impact on the sign structure of the many-body ground state wavefunction. It is demonstrated that the RNN ansatz we employ is able to treat systems with and without a sign problem in the ground state. For larger chains with up to 50 rotors, accurate properties, such as correlation functions and Binder parameters, are calculated. By employing quantum annealing, we show that precise entanglement properties can be obtained. All these properties allow one to identify a quantum phase transition between a paraelectric and a ferroelectric quantum phase. [ABSTRACT FROM AUTHOR]

A number of internal rotation codes can deal with the combination of one or two internal rotors with one 14N quadrupole nucleus, but once it comes to two 14N nuclei, no such code is available even for the case of one internal rotor. We present here the extension of our internal rotor program called BELGI-2N using the rho-axis method global approach to deal with compounds containing one methyl rotor and two weakly coupling 14N nuclei. To test our new code, we applied it to the microwave data recorded for N-methylimidazole, 2-methylimidazole, 4-methylimidazole, and 5-methylimidazole using a chirped-pulse Fourier transform microwave spectrometer in the 7.0–18.5 GHz frequency range. Compared to the previously published study, BELGI-2N was able to (i) significantly increase the number of assigned and fitted lines, (ii) fit the complete datasets considering both the internal rotation and the 14N nuclear quadrupole coupling effects simultaneously, and (iii) achieve standard deviations within the measurement accuracy for all methylimidazole isomers. [ABSTRACT FROM AUTHOR]

In this work, we perform a density matrix renormalization group study of chains of planar rotors interacting via dipolar interactions. By exploring the ground state from weakly to strongly interacting rotors, we find the occurrence of a quantum phase transition between a disordered and a dipole-ordered quantum state. We show that the nature of the ordered state changes from ferroelectric to antiferroelectric when the relative orientation of the rotor planes varies and that this change requires no modification of the overall symmetry. The observed quantum phase transitions are characterized by critical exponents and central charges, which reveal different universality classes ranging from that of the (1 + 1)D Ising model to the 2D classical XY model. [ABSTRACT FROM AUTHOR]

This paper presents the design of a complex‐step extended Kalman filter (CS‐EKF) to estimate the states of the twin‐rotor MIMO system (TRMS) which is a non‐linear system. Since the model of TRMS is quite complex and contains discontinuous functions, it is very difficult to calculate the Jacobian matrix in the TRMS analytically by hand. This makes it difficult to implement control methods that require Jacobian matrix calculation for TRMS. Herein, to calculate the Jacobian matrix, the CS‐EKF uses the complex‐step derivative approach, which is a numerical technique and offers near‐analytical accuracy in a single function evaluation. The effectiveness of the CS‐EKF is demonstrated through simulation and real‐time experiments. Also, The CS‐EKF is compared to the finite‐difference extended Kalman filter (FD‐EKF) and the unscented Kalman filter (UKF) in terms of estimation accuracy, computational load, and ease of implementation. [ABSTRACT FROM AUTHOR]

Owing to their high specific energy capabilities, ultramicrogas turbines (UMGT) are a high-potential technology to provide portable electric power supply for applications with demand of less than 1 kW. UMGT conceptual design is challenged by small-scale effects augmenting interdisciplinary dependencies leading to highly coupled, nonlinear component interactions. This work provides a novel approach to conceptual UMGT design by combining reduced order component and system modeling with constrained multi-objective optimization. Hereby, Part I presents integrated design and performance modeling of compressor, turbine, combustor, and generator. In Part II, the heat engine and generator modules are merged into a system framework by establishing conceptual UMGT rotor geometry and engine design. Following bearing selection and lifetime assessment, experimentally validated reduced order models are developed for heat transfer and rotordynamic analysis. Using the elaborated framework, a constrained multi-objective system optimization of a 300 W engine is performed based on ten design parameters and comparing SiAlON and Inconel 718 as potential rotor materials available for additive manufacturing. Hereby, bearing lifetime, system efficiency, and specific power are maximized while meeting rotordynamic, structural, and thermal requirements. Evaluating the results, interdisciplinary effects are highlighted, and two optimum engine configurations are suggested. [ABSTRACT FROM AUTHOR]

Ultramicrogas turbines (UMGTs) for electric power generation up to 1 kW are a viable replacement technology for lithium batteries in drones due to their high energy density. Previous research has shown that small-scale effects disqualify conceptual design practices applied to larger gas turbines owing to highly coupled, nonlinear component interactions. To fill this gap, we propose an interdisciplinary conceptual design and analysis framework based on reduced order models. To this end, the current work is divided into two parts covering component design and system integration, analysis, and optimization. In Part I, automated conceptual design of all engine subcomponents is elaborated facilitating interdependent reduced order models for compressor, turbine, combustor and high-speed generator while also considering additive manufacturing constraints. In a second step, the reduced order performance models are compared to computational fluid dynamics (CFD) Reynolds-averaged-Navier-Stokes (RANS) simulations of various turbomachinery geometries as well as experimental data of combustor and high-speed generator prototypes, showing good agreement and thus validating the component modules. In conclusion, the first part of this work elaborates an automated and efficient method to conceptual design of all components required for a functional UMGT. Since the strategy is applicable independent of component arrangement and engine layout, the proposed methods offer a universal framework for small gas turbine generators. [ABSTRACT FROM AUTHOR]

The demand for electricity is increasing tremendously globally with the development of countries. To fulfill the supply of electricity, many countries have already adopted renewable energy sources. The production of electricity from hydraulic energy sources is one of the oldest methods. The axial flow water turbine can efficiently generate energy from the water flow with a very low head. The current investigation is focused on enhancing the performance of the axial turbine by providing an enclosure around the rotor. The initial experiments were carried out with only the upstream enclosure. The optimized upstream enclosure was taken with different lengths of downstream enclosure for further investigations. The current investigation concluded that the maximum efficiency using only an upstream enclosure is 89.48%, which is around 3.20% higher compared with the bare turbine. The optimum efficiency was found at upstream-side length ratio (ULR)=0.46 (upstream enclosure length LU=40 mm). With using the optimum ULR=0.46 , the maximum efficiency for the downstream enclosure was found at downstream-side length ratio (DLR)=0.23 (downstream enclosure length LD=20 mm). The highest efficiency value for this axial runner was obtained at 90.89%, which is 4.83% higher compared with the bare turbine. [ABSTRACT FROM AUTHOR]

Flux reversal machine (FRM) belongs to the stator permanent magnet (PM) machine, which has the advantages of high reliability, high efficiency, and simple structure. However, large torque ripple and low torque density limit the development prospect of FRMs. Therefore, a wavy rotor FRM (WR-FRM) with curved stator slots is proposed, which can reduce the torque ripple while improving the average torque. The top surface of the rotor tooth consists of three sinusoidal functions, and the stator slots are constructed with a spline curve. To obtain better electromagnetic performance, the multi-objective genetic algorithm is used to optimize the FRM and the WR-FRM. Finally, the electromagnetic performances of the two machines is analyzed and compared by the finite element method. The results show that compared with the FRM, the torque generated by the unit volume of PM is increased by 36.47%, and the torque ripple is reduced by 62.7%. [ABSTRACT FROM AUTHOR]

This paper presents a reanalysis of four axial‐flow rotor simulation datasets to study the relationship between thrust and axial induction factor. We concentrate on high‐thrust conditions and study variations in induction factor and loads across the span of the different rotor blades. The datasets consist of three different axial‐flow rotors operating at different tip‐speed ratios and, for one dataset, also at different blockage ratios. The reanalysis shows differences between the blade‐resolved CFD results and a widespread empirical turbulent wake model (TWM) used within blade element momentum (BEM) turbine models. These differences result in BEM models underestimating thrust and especially power for axial‐flow rotors operating in high‐thrust regimes. The accuracy of BEM model predictions are improved substantially by correcting this empirical TWM, producing better agreement with blade‐resolved CFD simulations for thrust and torque across most of the span of the blades of the three rotors. Additionally, the paper highlights deficiencies in tiploss modelling in common BEM implementations and highlights the impact of blockage on the relationship between thrust and axial induction factors. [ABSTRACT FROM AUTHOR]

Occurrences of disturbance affect the rotor angle operation of a synchronous generator in the generation system of a power system. The disturbance will disrupt the synchronous generator's rotor oscillation and result in rotor angle instability, which will degrade the power system's performance. This paper aims to develop a Lyapunov-based rotor angle deviation regulator for the nonlinear swing equation of a synchronous generator. The proposed regulator is expected to assure asymptotic stability of the rotor angle and robustness to uncertainty. Backstepping and Lyapunov redesign techniques are employed in developing the regulator. To validate the effectiveness and robustness of the regulator, a simulation in MATLAB/Simulink is carried out. The simulation result shows that the asymptotic stability and robustness of the regulator are guaranteed regardless of the disturbance. [ABSTRACT FROM AUTHOR]

Non‐covalent chalcogen bond (ChB) interactions have found utility in many fields, including catalysis, organic semiconductors, and crystal engineering. In this study, the transition stabilizing effects of ChB interactions of oxygen and sulfur were experimentally measured using a series of molecular rotors. The rotors were designed to form ChB interactions in their bond rotation transition states. This enabled the kinetic influences to be assessed by monitoring changes in the rotational barriers. Despite forming weaker ChB interactions, the smaller chalcogens were able to stabilize transition states and had measurable kinetic effects on the rotational barriers. Sulfur stabilized the bond rotation transition state by as much as −7.2 kcal/mol without electron‐withdrawing groups. The key was to design a system where the sulfur σ ${\sigma }$ ‐hole was aligned with the lone pairs of the chalcogen bond acceptor. Oxygen rotors also could form transition state stabilizing ChB interactions but required electron‐withdrawing groups. For both oxygen and sulfur ChB interactions, a strong correlation was observed between transition state stabilizing abilities and electrostatic potential (ESP) of the chalcogen, providing a useful predictive parameter for the rational design of future ChB systems. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Solar Photovoltaic (SPV) penetration on the damping of critical and inter area modes arising from different penetration level of SPV into the Nigeria national grid has been studied. Also, the possible effects of SPV penetration on Critical Clearing Time (CCT) when a three-phase fault occurs on the grid are studied. The Nigeria 56-bus system was used for the investigation. Sensitivity analyses are carried out to obtain insight into how certain change in parameters affects both the transient and small signal stabilities of the Nigerian power systems. DigSILENT Power Factory was used for the simulation while the analysis was performed in MATLAB. Some of the important findings show that the grid developed increasing amplitude of oscillation from 20 % SPV penetration. There is no steady increase or decrease of CCT with penetration levels. The effect of changes in load on small signal conducted shows that both the real and imaginary load at Kano and Birnin kebbi bus should not exceed 257 MW, 176 MVAR and 171 MW, 134 MVAR, respectively so as to avoid system collapse. [ABSTRACT FROM AUTHOR]

Large components are crucial in modern industrial applications, especially for internal gap monitoring and specific assembly methods. This paper examines the assembly of hydroelectric generator rotors and stators, introducing a spatial relative position monitoring system using multiple sensors. A dedicated position monitoring program is designed, and error sources within the system are thoroughly explored. Detailed error analysis and modeling reveal that verticality and angular errors significantly impact monitoring accuracy. To address this, two error control methods are proposed to effectively mitigate these issues, ensuring precise assembly of large components. [ABSTRACT FROM AUTHOR]

Understanding the propulsion of a swimmer in a large group of individuals holds the key to unravelling the intriguing dynamics of active matter collective motion. Here, we develop a two-dimensional (2-D) self-assembled rotor, powered by bacterial flagella. At a water–air interface, the average direction of rotation of a rotor is fixed. When the chiral rotor is put into a 2-D bacterial suspension, we examine the average and fluctuation of the angular velocity of the rotor. Remarkably, the average angular velocity of a rotor is found to increase up to 3 times when the density of surrounding bacterial suspension increases and the increase is nonlinear. In a dense suspension of bacteria, the existence of a rotor disrupts vortices in the surrounding active turbulence, and the acceleration of the rotor is independent of the activity level of the surrounding free bacteria. The nonlinear acceleration thus results from hydrodynamic interaction with surrounding crowdedness that can be quantitatively explained by hydrodynamic simulation. The simultaneity between the acceleration of rotor and free bacteria in active turbulence suggests that crowding-induced acceleration may promote the onset of instability. The result will inspire new active-matter-based microfluidic devices with improved transport properties. [ABSTRACT FROM AUTHOR]

The unsteady numerical analysis method was utilized to investigate the unsteady flow structure of a contra-rotating ducted fan under crosswind conditions. The development and evolution mechanism of the lip vortex under the combined action of crosswind and rotor were studied. Two perspectives, namely the time-averaged flow field and unsteady time-frequency analysis, were employed for the examination. The results indicate that the unsteady aerodynamic forces exerted on the lip of the ducted fan are primarily influenced by four sets of frequencies, ranked in descending order of magnitude: 1 BPF (Blade Passing Frequency) of the upstream rotor, 1 BPF of the downstream rotor, the combined effect of the 1 BPF of the upstream rotor and 1 BPF of the downstream rotor, and 2 BPF of the upstream rotor. The maximum velocity occurs at the position where the inner surface of the windward side lip is inclined 40° from the freestream velocity direction, and a stable separation vortex is formed below this region. The lip separation vortex triggers the generation of blade suction side separation vortex in the upstream rotor, and its periodic formation, growth, shedding, and dissipation are the primary factors contributing to the unsteady flow. The research findings lay the groundwork for further advancements in active and passive flow control technologies under crosswind conditions. [ABSTRACT FROM AUTHOR]

Dynamic loads are inevitably generated during the operation of rotating machinery. In situ monitoring the dynamic loads is of great significance for assessing shafting health. Triboelectric nanogenerator (TENG) is sensitive to motion but not suitable for load monitoring, while piezoelectric nanogenerator (PENG) is just the opposite. Therefore, the combination of the two can complement each other. From this, a dynamic load monitoring smart bearing (DLMSB) integrated with TENG and PENG is proposed. The specially designed TENG can produce an “M‐waveform”, which can be used to extract rotation frequency and distinguish the quadrant of the rotor. Meanwhile, applying PENG to capture the load condition of the bearing, and referring to the main frequency of M‐waveform, it is convenient to obtain the dynamic loads of shafting. Furthermore, a real‐time monitoring system is developed, which can realize not only real‐time monitoring of the rotation speed and dynamic loads magnitude but also the quadrant discriminating of dynamic loads. The results have shown that the monitoring error for dynamic loads is 3 N or 5.5%, and the accuracy rate for determining the quadrant of the dynamic loads can reach 93%. This study provides a novel approach for the in situ monitoring of mechanical operating status via nanogenerators. [ABSTRACT FROM AUTHOR]

This paper investigates the idea of substituting the first stage of a conventional axial-flow compressor and its inlet guide vane (IGV) row with a variable rotor tandem (VRT) stage to reduce the size and weight of axial-flow compressors. It is expected that a tandem stage gains higher pressure ratio than a conventional stage, and simultaneously, its variable stagger rotor provides more flexibility in handling unsteady phenomena at low mass flow rates. A three-dimensional numerical model based on Reynolds-Averaged Navier–Stokes equations is developed to conduct this investigation. To validate the numerical model, experimental tests are conducted on a tandem single-stage axial-flow compressor test bench in the Dana laboratory of Amirkabir University of Technology, to compare the performance map with numerical results. The validated numerical model is then employed to simulate the performance of both front and aft variable rotor blades. The proposed tandem stage effectively performs the IGV duty, suppresses instabilities at low mass flow rates, and eventually extends the compressor's stable operational range. This proves that a VRT stage is an efficient active surge-control system tool. The detailed survey of the three-dimensional flow field reveals that the aft tandem rotor blade stagger angle is more effective in increasing the stall margin and decreasing the minimum operational mass flow rate than the front row of blades. It is observed that when the aft blades rotate in the direction of decreasing the tandem blades' gap area, the flow momentum increases and causes the compressor stability at lower mass flow rates. [ABSTRACT FROM AUTHOR]

Deep transfer learning is frequently employed to address the challenges arising from limited or hard-to-obtain training data in the target domain, but its application in axial compressors has been scarcely explored thus far. In this paper, a multi-objective optimization framework of a transonic rotor is established using deep transfer learning. This framework first pre-trains deep neural networks based on the peak efficiency condition of 100% design speed and then fine-tunes the networks to predict the performance of off-design conditions based on the small training dataset. Finally, the design optimization of the transonic rotor is carried out through non-dominated sorting genetic algorithm II. Compared to neural networks that are trained directly, transfer learning models can achieve higher prediction accuracy, particularly in scenarios with small training datasets. This is because the pre-trained weights can offer a better initial state for transfer learning models. Moreover, transfer learning models can use fewer samples to obtain an approximate Pareto front, making the optimized rotor increase the isentropic efficiency at both peak efficiency and high loading conditions. The efficiency improvement of the optimized rotor is attributed to the reduction of the loss associated with the tip leakage flow by adjusting the tip loading distribution. Overall, this study fully demonstrates the effectiveness of transfer learning in predicting compressor performance, which provides a promising approach to solving high-cost compressor design problems. [ABSTRACT FROM AUTHOR]

In practical optimization design, an excessive number of design variables have a highly detrimental influence on the efficiency and accuracy of the final design scheme and expose the optimization problem to the curse of dimensionality. Therefore, incorporating only the most essential variables into an optimization design problem facilitates obtaining accurate and cost-efficient solutions. Reported here is an optimization design method based on parameter reduction and active subspaces, and it is used to redistribute the tip load in a transonic fan. Specifically, a coupled design strategy is developed to reduce the number of parameters needed to describe the three-dimensional blade shape, which leads to far fewer design variables being involved in the optimization design. Moreover, active subspaces are used to perform sensitivity analysis and establish low-dimensional surrogate models. After the coupled design, a blade is represented effectively by only three parameters, each of which has a significant influence on the fan performance. Three one-dimensional active subspaces are established for maximum mass flow rate, maximum total pressure ratio, and maximum efficiency, based on which the linear surrogate models are obtained. Next, the chordwise tip blade loading is optimized, after which the rotor efficiency at the design point is increased by 1.1%, while the total pressure ratio remains nearly unchanged. Finally, the flow field is analyzed to understand the mechanism for this performance improvement, and the results show that the optimized blade loading reduces the aerodynamic losses caused by shock-induced flow separation and the interaction between shocks and tip leakage flows. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to describe a numerical simulation method of ice accretion on BO105 helicopter blades for predicting the effects of trailing edge flap deflection on ice accretion. Design/methodology/approach: A numerical simulation method of ice accretion is established based on Myers model. Next, the shape and location of ice accretion of NACA0012 airfoil are calculated, and a comparison between calculated results and experimental data is made to validate the method. This method is used to investigate the effect of trailing edge flap deflection on ice accretion of a rotor blade. Findings: The numerical method is feasible and effective to study the ice accretion on helicopter rotor blades. The downward deflection of the trailing edge flap affects the shape of the ice. Practical implications: This method can be further used to predict the ice accretion in actual flights of the helicopters with multielement airfoils. Originality/value: The numerical simulation method here can lay a foundation of the research about helicopter flight performance in icing condition through predicting the shape and location of ice accretion on rotor blades. [ABSTRACT FROM AUTHOR]

This study investigates turbine rim seal geometry effects within the rotationally-driven ingestion regime. Computations were performed with a wall-resolved unsteady Reynolds-averaged Navier-Stokes (URANS) model and a large-eddy simulation (LES) model including near-wall boundary layer modeling, that is, wall-modeled LES (WMLES). Use of simplified rim sealing models is proposed as an efficient method of ranking seal designs and investigating sensitivity to seal geometry. Four rim seal configurations, two chute seals, an axial seal and a radial seal which are representative of those used in gas turbines and in previous research were investigated. Furthermore, hybrid seals combining geometric characteristics from both the chute and radial seal were considered. Significant sensitivities of sealing performance to turbulence modeling are identified, but URANS and WMLES show similar trends in ranking of seal performance, and these are consistent with previous experimental work. The addition of an outer radial clearance section to a chute seal is effective in reducing ingestion levels. [ABSTRACT FROM AUTHOR]

In Part I, a companion paper of the two-part article, a subsonic turbine stage and a transonic one conditioned at the same Reynolds number, flow coefficient, loading coefficient and reaction, but two different exit Mach numbers are designed to provide a direct contrast between a high-subsonic and a transonic flow conditioning for rotor blade squealer tips. In this paper as Part II, further analyses are carried out to address the main issues of interest arising from Part I: first, to identify the driving flow physical mechanisms for the contrasting aerodynamic efficiency sensitivities of the two stages; second to seek a more suitable heat transfer objective function for the tip aerothermal design optimization, given the seemingly strong conflicts among those conventionally adopted heat transfer objective functions. Two counter-rotating tip vortical structures, the pressure side vortex (PSV) and the casing-driven cavity vortex (CCV), are shown to impact the aero-performance differently between the two stages. For the subsonic stage, the leakage flow is strongly affected by a stronger residual PSV at the squealer cavity exit. For the transonic stage however, the tip choking in limiting the over tip leakage (OTL) mass flow and favorable pressure gradient in a transonic flow over a separation bubble led to a much stronger and more persistent CCV and thus lower aero-effectiveness of squealer tip for the transonic stage. The two vortices also show major heat transfer signatures on the cavity surfaces by impingement. For the PSV, the impingement impact is mainly on the cavity floor. For the CCV, on the other hand, its impact is mainly on the inner side-wall of the suction side rim. The latter is found to be mainly responsible for the overall linear variations of the heat load with the squealer height. Again, the relative strength between PSV and CCV serves as an effective differentiator in the heat transfer performance. The stronger and more persistent CCV in the transonic stage results in a strong signature on a large portion of the suction side cavity inner sidewall, thus a much higher increment in heat transfer with the squealer height than that for the subsonic stage. In seeking to establish a more consistent heat transfer objective function for combined aerothermal design and optimization, a coolability weighted nonuniformity parameter is proposed to integrate the local heat transfer and the coolability. The proposed objective function is shown to lead to consistent Pareto fronts for the combined aerothermal performance sensitivities, particularly for the present cases with strong heat transfer nonuniformity which are particularly challenging to those conventional treatments as shown in Part I. The coolability-augmented objective function should thus serve as an enabler to help practical applications of blade tip aerothermal design optimizations. [ABSTRACT FROM AUTHOR]

Rotor blade tip has significant influence on turbine stage aerodynamics and heat transfer. Most previous efforts have been based on low-speed cascade settings. However, more recent research on transonic blade tips exhibits distinctive flow features with qualitatively different performance sensitivities. These prompt two key issues of interest on the related flow conditioning. First, the contrast between a low-speed flow and a transonic regime highlights the less studied high-subsonic flow regime, closely relevant to many realistic turbine designs. Second, the relative casing movement and upstream inflow conditions, known to have non-negligible effects, indicate the need to examine a rotor blade tip in a realistic stator-rotor stage environment, which is also lacking. To elaborate the Mach number effect in the flow regimes of practical interest, we aim to examine a high subsonic stage in a direct and consistent comparison with a transonic one. To this end, a high subsonic stage (exit Mach number of 0.7) and a transonic (exit Mach number of 1.1) are designed at the same Reynolds number with a three-dimensional parameterization and meshing system. The tip squealer height is used as a representative parameter to investigate the sensitivity of the stage aerothermal performance. The multi-objective optimization using the Kriging surrogated model is employed to identify the Pareto fronts for the stage efficiency and the heat transfer. The comparison of the optimized results between these two stages shows distinctively different trends in the performance variation with the squealer height. The efficiency of the subsonic stage increases with the squealer height reaching a plateau. In contrast, the efficiency in the transonic stage first increases and then drops to the level comparable to that of a flat tip. Significantly, the present results indicate, for the first time, that the squealer tip in a transonic stage may not be as effective as in a subsonic stage. On the other hand, for heat transfer, sensitivity variations are more complex. The overall heat load and the local nonuniformity lead to qualitatively different sensitivities with the squealer height, as well as completely incomparable Pareto fronts. These observed heat transfer sensitivities raise the question on how to effectively conduct a combined aerodynamic and heat transfer performance design optimization. The authors subsequently resort further aerothermal physics analyses described in a companion paper as Part II of the two-part article. In Part II, the physical interpretation of the contrasting aero-efficiency sensitivities for the two stages, as well as a physical understanding leveraged selection of the objective function for such combined blade tip aerothermal optimization will be presented. [ABSTRACT FROM AUTHOR]

In recent years, wind power generation has been promoted as a countermeasure to global environmental problems. However, the introduction of many wind power generators into the power system may cause system frequency fluctuations. This paper proposes a control method to reduce system frequency fluctuations by using the rotor kinetic energy (RKE) of a variable speed wind turbine (VSWT). When the frequency falls, this method suppresses fluctuations by consuming RKE to increase VSWT power generation, and when it rises, it decreases VSWT power generation by accumulating RKE. The effectiveness of this method is confirmed through simulations using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

Purpose: Elastic rings served as the elastic supporting elements which have been extensively used in the aeroengines for maneuverable planes with high overloading. However, under extreme conditions, the elastic ring contacts the bearing seat, causing elastic ring failure. Therefore, it is necessary to optimize the matching parameters of the elastic ring in order to suppress the occurrence of elastic ring failure under harsh working conditions. Design/methodology/approach: In this paper, a rotor system supported by elastic rings is researched and a multi-objective parameter matching method of elastic ring is proposed, considering the elastic ring failure, rotor system's frequency forbidden zone and rotor system's dynamic response. Then, the particle swarm optimization algorithm is used to dynamically constrain the parameter matching space and obtain the ideal solution for the elastic ring parameter matching. Findings: By analyzing the elastic ring's matching results (different unbalanced forces and disk masses), the relationship between the trend of Pareto front changes and rotor system parameters is studied. In addition, the rotor system's dynamic characteristics before and after parameter matching are analyzed. Originality/value: This article provides guidance for the design of elastic rings by matching the parameters of elastic rings. [ABSTRACT FROM AUTHOR]

Assembly errors can lead to the eccentricity of rotors, further resulting in angular misalignment of rotors and inducing some secondary misalignments, such as the angular misalignment of gears and tilt misalignment of the inner ring of bearings (TMIRB). Ultimately, these misalignments can lead to rubbing faults. However, these misalignments have not raised significant concern, this article investigates their influence on the vibration responses of a dual-rotor-gear-bearing system with rubbing. First, a finite element model (FEM) of the system is built by using an in-house beam element code, and the nonlinear force model of the bearing is established based on the Hertz contact theory. Then, a new model to simulate angular misalignment of gears is proposed by changing the time-varying meshing stiffness (TVMS). Furthermore, the nonlinear dynamic characteristics of the system are investigated in detail under different misalignment angles and rotating speeds, and some interesting conclusions are summarized as follows. Specifically, analyses of the spectrum cascade of radial and axial responses reveal the presence of rich multi-time frequencies and combined frequencies. Moreover, as the misalignment angle increases, the system experiences partial rubbing, the rotating speed threshold (RST) corresponding to initial rubbing decreases, and the mesh stiffness of gears decreases. In summary, the proposed model and the results of the analysis offer valuable insights into the vibration characteristics of such systems and these findings can be instrumental in optimizing their design and operation. [ABSTRACT FROM AUTHOR]

Wind turbines can freeze due to exposure to cold air. Ice formation on the rotor blades of a wind turbine reduces their performance. In the present work, the effects of ice formation on rotor blades of straight-blade vertical-axis wind turbines (SBVAWT) with a three-blade rotor and a NACA 0021 airfoil are numerically evaluated under two-dimensional transient settings by solving the continuity, momentum and turbulence equations become in ANSYS FLUENT. Grid and time step independence was investigated. For validation, the numerical model was compared with experimental data. An experimental ice model from the literature was then used to numerically simulate the iced rotor in twodimensional transition settings. The numerical simulation of the icy rotor was compared with an ice-free rotor. It was found that ice formation on the rotor blades changed the velocity and pressure fields around the rotor blades at angles of 180-360°, changing the streamlines and increasing the vortices. Furthermore, the maximum and minimum reductions in moment coefficient during blade icing occurred at angles of 225-315° and 45-135°, respectively. Due to ice formation on the rotor blades, the power coefficient of the rotor blades at angles 180-360° decreased drastically, and the power coefficient of the iced rotor was smaller than that of an ice-free rotor. It was concluded that ice formation on the blades of the SBVAWT reduced the average power coefficient of the blades and rotor power coefficient by 94.2% and 95%, respectively. [ABSTRACT FROM AUTHOR]

A better understanding of the flow field is crucial for improving the design of a turbomachine. In this work we investigate the performance of voluteless centrifugal fan rotors. The study includes two parts: experiments and numerical simulations through Computational Fluid Dynamics (CFD) techniques. Our test system allows the analysis of the flow behavior of centrifugal fan rotors maintaining the meridional shape without making substantial changes to their internal structure, but with different blade shapes, sizes, and blade numbers. To avoids irregular interference with the rotor flow from external components such as the collector a radial channel composed by two parallel discs was placed concentrically on the rotor axis at its outer periphery with special interest in measuring flow characteristics at the rotor outlet with a reliable accuracy. As an application case a typical centrifugal fan rotor with ten blades of single curvature in the circular arc shape has been investigated. Two types of measuring systems were used: one, with an aerodynamic probe located in the centrifugal rotor outlet and, the other, with a load cell for measuring the rotor shaft power. A comparison of the results by these two measuring arrangements shows some important characteristics, such as the phenomenon of the flow recirculation within the rotor. The experimental performance curves related to non-dimensional flow such as the slip factor, and pressure coefficient, revealed good matching with numerical simulations, highlighting the remarkable reliability of our experimental setup. [ABSTRACT FROM AUTHOR]

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During the operation of a reversible pump-turbine, a hump area can easily appear under the pump condition, which will greatly affect the performance of a storage unit, with pressure pulsation being the key factor for the stable operation of a pump-turbine. Therefore, in order to explore the pressure pulsation characteristics of each flow component in the hump area, this paper first compared the full characteristics of the model test under different working conditions, and then it analyzed the pressure pulsation characteristics. By analyzing the pressure pulsation characteristics in the unit's flow component under different flow rates in the hump area, the pulsation rule of a pump-turbine running in the hump area was revealed. It was found that the peak-to-peak value of the draft tube in the hump area was the smallest under the optimal flow condition, and the peak-to-peak value increased along the flow direction, with the rotor and stator interaction (RSI) effects being continuously enhanced. When away from the runner basin, the influence of RSI gradually weakened after leaving the runner. No low frequency was found in the optimal traffic. The peak-to-peak value of the low flow condition increased compared with the optimal flow condition, and the distribution was not uniform. The main frequency of the whole basin was relatively complex, indicating that the flow of water was unstable in the condition of partial load, resulting in the hump area during the unit operation. The research results can provide a theoretical reference for improving the stability of pump-turbines. [ABSTRACT FROM AUTHOR]

Rotor bar breakage in induction motors is often detected by analysing the signatures in the stator current. However, due to the alteration of the current spectrum, traditional methods may fail when inverter-fed motors operate with closed-loop control using a cascade structure to regulate the speed. In this paper, the potential of zero-sequence voltage analysis to detect this fault is investigated, and a new index to quantify the severity of the fault based on this signal is proposed. Signals from motors operating under different control strategies and signals from motors powered from the mains are considered to verify the robustness of the proposed fault severity index. As a result, in all the analysed conditions the value of the proposed index for the healthy motor is found to be approximately 0.010, while for the faulty machine it is between 0.110 and 0.252. [ABSTRACT FROM AUTHOR]

This research focuses on a novel convertible unmanned aerial vehicle (CUAV) featuring four rotors with tilting capabilities combined with a tapered form. This paper studies the transition motion between multirotor and fixed-wing modes based on the mechanical and aerodynamics design as well as the control strategy. The proposed CUAV involves information about design, manufacturing, operation, modeling, control strategy, and real-time experiments. The CUAV design considers a fixed-wing with tiltrotors and provides the maneuverability to perform take-off, hover flight, cruise flight, and landing, having the characteristics of a helicopter in hover flight and an aircraft in horizontal flight. The manufacturing is based on additive manufacturing, which facilitates the creation of a lattice structure within the wing. The modeling is obtained using the Newton–Euler equations, and the control strategy is a PID controller based on a geometric approach on SE(3). Finally, the real-time experiments validate the proposed design for the complete regime of flight, and the research meticulously evaluates the feasibility of the prototype and its potential to significantly enhance the mission versatility. [ABSTRACT FROM AUTHOR]

This paper proposes the circulation redistribution for the low-pressure (LP) rotor of a highly-loaded vaneless counter-rotating turbine (VCRT) to reduce the LP shock losses. The method is to decrease the mid-span circulation and increase the tip circulation at the exit of the LP rotor with unchanged high-pressure (HP) and LP power output. The LP Blade-to-Blade flow field can be considered as a Laval nozzle model. And the high static pressure drop from the throat to the exit results in strong trailing edge (TE) shocks near the LP mid-span. Also, the suction side TE shock (ST) and the reflected shock of the pressure side TE shock (RPT) near the LP mid-span merge into a relatively strong shock very close to the TE. These two factors result in high shock losses. To reduce the shock losses under the design condition, decreasing the stagger angle and the blade exit angle near the LP mid-span are adopted to reduce the LP mid-span exit circulation. This changes the throat area to exit area ratio near the LP mid-span, prompting the actual static pressure drop from the throat to the exit to be reduced and closer to the theoretical value, so that the TE shock strength is reduced. Besides, the intersection of the RPT and the ST is delayed owing to the improved flow angle distributions near the TE, further contributing to the LP mid-span shock loss reduction. Since the LP power output is decreased and the LP tip-leakage flow (TLF) losses are far lower than the HP TLF losses, increasing the stagger angle and the blade exit angle in LP tip regions are employed to increase the LP exit circulation and decrease the HP exit circulation in tip regions. Then the HP and LP efficiency are both raised with unchanged HP and LP power output after optimizing the blade profiles near the mid-span and in tip regions of the LP rotor. The remarkable thing is that the TE shock strength in LP tip and root regions are both reduced after improved because of the decreased ratio of the exit area to the throat area. And the intersection of the RPT and the ST in LP tip and root regions are also both delayed, leading to reduced shock losses. The reduced TE shock losses along the whole LP span appreciably raise the LP and VCRT efficiency by 0.96% and 0.32% respectively. [ABSTRACT FROM AUTHOR]

A novel octocopter with an overlapping rotor arrangement is proposed in this paper to increase the payload with a limited size. The aerodynamic performance was obtained by both experiments and numerical simulations with the rotor spacing ranging from 1.2 D to 2.0 D ( L = 1.2   D ,   1.4   D ,   1.6   D ,   1.8   D ,   2.0   D ). Also, the aerodynamic parameter was evaluated by the thrust, power consumption, thrust coefficient, power coefficient, and figure of merit (FM) in hover. Compared with a traditional co-axial octocopter, the results indicated that the overlapping octocopter at L = 1.8   D presented an increasing thrust up to 15.98%, and the FM increment was up to 6%. Additionally, the streamline distribution showed that the symmetry of the vortex movement in the downwash flow for the overlapping rotors will offset the rotor interference with an increase in thrust. Meanwhile, the vortex deformation resulting from the induced velocity from the upper rotor also led to an increase in power consumption. Finally, the optimal aerodynamic performance of the overlapping octocopter was obtained with a rotor spacing of L = 1.8   D at 1800 RPM. [ABSTRACT FROM AUTHOR]

Wind and gusts can significantly impact the performance of rotors and turbines. The transient behavior of the rotor should be carefully examined to account for these effects. This paper investigates the unsteady aerodynamic characteristics of a rotor blade under different wind conditions, such as direction, speed, and angle. A 3D transient Computational Fluid Dynamics (CFD) simulation using the dynamic mesh technique is performed to analyze the rotor dynamics. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations with the k-ω SST turbulence model are solved. The rotor blade used for this study is the U15XXL Combo KV29 industrial blade, which has not been numerically analyzed before. The results show that wind in the same direction as the rotation reduces the thrust more than lateral or opposite wind. Lateral wind with a speed lower than 5 m/s decreases the blade performance, but higher speeds increase it. Higher lateral wind speeds also cause two peaks in the torque curve, forming a butterfly wing shape in the polar torque plot and multiple extrema in the torque curve with increasing speed. The maximum thrust shifts slightly to the left with increasing lateral wind speed. The lateral angle does not affect the average thrust produced in one blade revolution but only causes a spatial shift. The thrust production decreases as the angle approaches the opposite direction of rotation. The motion amplitude decreases, and the curve becomes smoother as this angle increases. A nearly straight line similar to no side wind is observed at 60 and 90 degrees, which is attributed to the constant effective angle of attack during the rotation cycle. [ABSTRACT FROM AUTHOR]

This paper investigates the formation of vibration fields in a mechatronic setup driven by dual induction motors, relying on the controlled synchronization of unbalanced rotors. The proposed algorithm enables precise control over rotor speeds and phase shifts. Experimental results from a multi-resonance vibration laboratory setup demonstrate this approach's ability to form the vibration fields. The ability to control these fields is crucial for applications such as vibratory transportation and the mixing of bulk materials. The results obtained can ensure a diverse picture of the complex trajectories of motion for various points of the platform, primarily in the screens, making various useful effects for vibration technologies. Additionally, the practical value of this research is that in the case of double synchronous mode the ordinate of the lower point of the trajectory is lower than in the case of single synchronous mode, which improves the efficiency of unloading and prevents congestion formation. The experimental data highlight the practical advantages and potential improvements in efficiency and reliability offered by this method. [ABSTRACT FROM AUTHOR]

Recently, fault diagnosing supervised classifiers have been widely proposed to diagnose both electric and mechanical faults in induction motors (IM). However, many of them require a large amount of data, which implies a great effort required for processing fault-related features and building the training set. Furthermore, in real-world datasets, it is required to deal with highly skewed data distributions, also known as class imbalance, which is a limiting issue and can misguide the tuning of machine learning algorithms. Resampling techniques based on a synthetic generation of minority class observations aim to address this problem. Last but not least is the fact that inverter-fed IM introduces undesired harmonics in the monitoring signal altering the diagnosis patterns. This diagnosis scheme is evaluated on experimental imbalanced data oriented to deal with the diagnosis of a rotor in situations where it is fed with an inverter. The results show how this imbalanced approach determines the actual diagnosis performance on a small amount of data. The experimental results demonstrate that balanced training sets built with class balancing techniques improve the classifier and therefore its performance for diagnosing incipient rotor faults in inverter-fed IM with studied and interpretable features recently proposed in this field of study. [ABSTRACT FROM AUTHOR]

The operational state of a rotor system directly affects its working efficiency, and the axis trajectory can accurately characterize this state. Therefore, a method for extracting axis motion trajectory characteristics based on distance sequence representation is established. First, the axis trajectory sample signal is constructed from the original vibration displacement signal. Singular value decomposition (SVD) is performed on the sample signal to obtain effective components, resulting in a purified and denoised axis motion trajectory signal. Next, the axis motion trajectory signal is centralized and normalized. Feature extraction is then performed on the axis motion trajectory signal. Based on the different curvatures of various regions in the axis motion trajectory graph, data points are adaptively selected. The distances between the selected data points and a unique fixed point are calculated in the two-dimensional plane, resulting in a feature signal that characterizes the axis motion trajectory graph. This completes the extraction of the axis motion trajectory characteristics. Different rotational speeds, additional weights, and changes in rotor arrangement types are applied to a multi-disk rotor test rig to obtain measured data for various unbalanced states, validating this method. The results show that this method effectively characterizes the axis motion trajectory with strong generality. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to find the characteristics of supercritical airfoil in helicopter rotor blades for hovering phase using numerical analysis and the validation using experimental results. Design/methodology/approach: Using numerical analysis in the forward phase of the helicopter, supercritical airfoil is compared with the conventional airfoil for the aerodynamic performance. The multiple reference frame method is used to produce the results for rotational analysis. A grid independence test was carried out, and validation was obtained using benchmark values from NASA data. Findings: From the analysis results, a supercritical airfoil in hovering flight analysis proved that the NASA SC rotor produces 25% at 5°, 26% at 12° and 32% better thrust at 8° of collective pitch than the HH02 rotor. Helicopter performance parameters are also calculated based on momentum theory. Theoretical calculations prove that the NASA SC rotor is better than the HH02 rotor. The results of helicopter performance prove that the NASA SC rotor provides better aerodynamic efficiency than the HH02 rotor. Originality/value: The novelty of the paper is it proved the aerodynamic performance of supercritical airfoil is performing better than the HH02 airfoil. The results are validated with the experimental values and theoretical calculations from the momentum theory. [ABSTRACT FROM AUTHOR]

Under time-varying loads, the stator current of cage motors shows non-stationary and non-periodic, which makes the existing rotor broken bar fault identification method under time- varying loads fail to diagnose due to the influence of the fundamental frequency modulation of the current. This paper proposes a time-varying load cage motor diagnostic method based on the Teager-Kaiser energy operator (TKEO), a new method for rotor broken bar fault diagnosis. The method used TKEO to extract the instantaneous frequency of the current signal to determine the severity of the broken bar fault of the motor. In order to verify the effectiveness and superiority of the method the current signals under different health states and different load conditions were ex- perimentally obtained and diagnosed. The analysis results were also compared with the traditional method. In multiple dimensions. The results show that this method is able to distinguish the health state of the motor more accurately under time-varying loads and has stronger robustness. to load disturbances; especially under light-load operation. the numerical difference of the relative change gradient of the method is 4~6 times higher in comparison with that of the traditional method. In addition, the extracted fluctuation range of the fault frequency is more concentrated in the range between 0~5 Hz. [ABSTRACT FROM AUTHOR]

Vibration testing of an integrally bladed rotor (IBR) is often completed through traveling wave excitation (TWE) bench tests composed of multiple, simultaneously excited inputs. Often, each blade has many output locations. For IBRs with many blades, as often found in the high pressure compressor, the total number of outputs can be several orders of magnitude. Formulation of a full output spectral density matrix from all measurements will then contain an exponential number of values at each frequency bin that can be detrimental to computational resources during the spectral density matrix formulation as well as down-stream system identification algorithms. An online algorithm is proposed for collecting and analyzing TWE data to reduce the large, computationally burdensome datasets into a manageable number of subsets for subsequent system identification. Furthermore, a frequency domain decomposition technique is also proposed for system identification that also attempts to reduce the data size through singular value decomposition. Identified system poles can be averaged from each subset, but mode shapes require stitching each subset together to identify the full mode shape at all output locations. The developed approaches are tested on synthetic TWE data and compared to baseline system identification results obtained using the full spectral density matrix. Results indicate the data subsets accurately compare to the baseline without much loss in accuracy. [ABSTRACT FROM AUTHOR]

In order to enhance the stability of the tilt transition process, a new configuration of Quad-Tiltrotor UAV was presented in this paper. Firstly, numerical simulation was used to calculate and analyze the aerodynamic interaction between the front rotor/fuselage/rear rotor during the transition state mode. The calculation model of the isolated rotor, front-rear rotor, front rotor-fuselage, and front rotor-rear rotor-fuselage combination states are established. Besides, the effects of pitch, roll, and yaw moment on the fuselage at different tilt angles are analyzed. It is concluded that the front rotor is the leading factor in the aerodynamic interference of the whole UAV in the different combination states. The research results can provide a reference for the optimization design of the overall layout, structure, and flight control strategy of the cross-shaped quad-tiltrotor UAV, and can also provide solutions for the logistics application of urban air traffic. [ABSTRACT FROM AUTHOR]

To address the problems of large sliding mode chatter and phase delay in the traditional first-order flux sliding mode observer, a HOT FSMO (High-Order Terminal Flux Sliding Mode Observer) based on an improved tracking differentiator is proposed in this study. A high-order sliding mode control law is designed to achieve chatter suppression of flux linkage estimation, and a new tracking differentiator with low chatter containing a terminal attractor is combined to replace the conventional low pass filter to achieve accurate tracking of the flux linkage and rotor position, as well as filtering functions. The experimental results show that the HOT FSMO based on the novel tracking differentiator can effectively reduce the sliding mode chattering and decrease the position estimation error, while speeding up the system response and improving the system dynamic performance under different speed and load conditions when compared with the traditional linear flux linkage sliding mode observer. [ABSTRACT FROM AUTHOR]

Compared with the quad rotor UAV (Unmanned Aerial Vehicle), the large twin rotor UAV has the advantages of lower price, longer endurance and higher efficiency, but it has serious coupling and poor anti-in-terference ability. To solve these problems, this study proposes a dual rotor control algorithm using variable universe fuzzy PID (Proportional Integration Differentiation). In this study, the UAV system is divided into position control and attitude control. In attitude control, fuzzy PID is used to adjust the parameters of PID in real time to improve the stability of UAV. According to the motion mode of UAV, a new type of UAV structure is proposed, and the dynamic model of double rotor is established, and the simulation model is built on Simulink for verification. The results show that the proposed algorithm reduces the overshoot by 50% when compared with the ordinary PID control algorithm, which indicates that the proposed algorithm has better stability on large twin rotor UAV and can recover faster in case of interference. [ABSTRACT FROM AUTHOR]

Pre-stall disturbances and rotating instability (RI) are two typical phenomena observed in axial compressors prior to stall. In this study, experimental measurements and numerical simulations were employed to investigate the relationship between pre-stall disturbances and RI and their physical mechanisms in an axial compressor rotor with a non-uniform tip clearance gap. A post phase-locking technique was used in analyses of pressure fluctuations in the blade tip region. The resulting power spectrum estimation indicated that pre-stall disturbances shared the same frequency characteristics as RI, but differed in their spatial distribution. Pre-stall disturbances were the result of the upstream migration of RI. Numerical simulation results, validated by experimental measured distribution of pressure fluctuations, showed that the tip leakage vortex originating from the large blade tip clearance underwent a spiral-type breakdown, which was the originating mechanism of RI. When the back flow vortex generated by breakdown encountered the blade leading edge due to throttling, pre-stall disturbances were detected at the blade leading edge. [ABSTRACT FROM AUTHOR]

This paper aims to design a deformable mechanism to drive amphibious rotor blade deform from an aerial shape to an aquatic one. The Bennett four-bar and spherical four-bar mechanisms are used as the basic units (B unit and S unit) to form the Bennett–spherical spatial scissor unit (BS unit). By analyzing the kinematic characteristics of the BS unit, it is found that the BS unit can achieve the spatial deformation of expansion and torsion, effectively improving the rotor's performance in water and air media. The wing rib support structure, which is fixed to the BS unit linkage, is designed. The coordinate transformation method describes the blade shape in aerial and aquatic modes using BS unit and rib parameters. To improve the rotor blade performance in air and water, the rotor blade design is carried out under the NSGA-II framework with BS parameters as the design variables. The Gaussian regression and CFD methods are applied to build a surrogate model to reduce the computational cost. The results show that the expansion–torsional deformation of the BS unit can effectively increase the air and water compatibility of the rotor blades. When the rotor is an aerial shape, the BS mechanism extends and decreases the torsion to increase the lift and efficiency. When it is deformed to an aquatic shape, the BS mechanism reduces its length and increases the torsion to reduce the torque effectively. The BS scissor unit and the design method can be effectively applied in the design of deformable rotor blades. [ABSTRACT FROM AUTHOR]

In rotating machinery with a multi-stage assembled rotor, such as is found in aero engines, any unbalance present will undergo unknown changes at each stage when rotating the assembly phases of the rotor. Repeated disassembly and adjustments are often required to meet the rotor's residual unbalance specifications. Therefore, developing a prediction model of this two-sided unbalance for a multi-stage assembled rotor is crucial for improving the first-time assembly pass rate and assembly efficiency. In this paper, we propose a prediction model of the two-sided unbalance seen in the multi-stage assembled rotor of an aero engine. Firstly, a method was proposed to unify the mass feature parameters of each stage's rotor into a geometric measurement coordinate system, achieving the synchronous transmission of geometric and mass feature parameters during the assembly process of the multi-stage rotor. Building upon this, a linear parameter equation of the actual rotation axis of the multi-stage rotor was established. Based on this axis, the mass eccentricity errors of the rotor were calculated at each stage, further enabling the accurate prediction of two-sided unbalance and its action phase in a multi-stage rotor. The experimental results indicate that the maximum prediction errors of the two-sided unbalance and its action phase for a four-stage rotor are 9.6% and 2.5%, respectively, when using this model, which is a reduction of 53.0% and 38.1% compared to the existing model. [ABSTRACT FROM AUTHOR]

Literature indicates that there is lack of study related to the effects of axially skewed blades on the aerodynamic performance of axial flow fans. In this study rotors of various blade skews, namely, axial, circumferential and axial-circumferential types, are studied and their aerodynamic performances are compared to those of the baseline radial rotors of two types, namely, constant chord and varying chord. The skew in a blade can be considered as combination of sweep and dihedral. The skew change from the circumferential to axial type causes reversal of dihedral induced radial blade force and hence a reversal of meridional streamline curvature which in turn reverses the modulation of the end-wall loads. The inherent forward sweep in the forward skewed blades also modulates hub and tip loads. Thus, in a forward axial skew blade the forward sweep and positive dihedral combine favorably to unload the tip and to upload the hub. In the forward circumferentially skewed blades, forward sweep and the negative dihedral have mutually countering effects on end-wall load modulation. The highlight of this study is that it has demonstrated experimentally the unloading of the tip in the forward axially skewed blades which resulted in reduced losses and better performance including increased stall margin. Reduced tip loading was also verified from the casing pressure sensor measurements which showed weakening of tip vortex. The relative influence of sweep and dihedral on performance was additionally demonstrated in the axially-circumferentially skewed rotor of the constant chord type, with improvements attributable to higher sweep. [ABSTRACT FROM AUTHOR]

This study explores the implications of the number of blades on the performance of both open and shrouded rotors. By conducting a thorough experimental analysis at a fixed solidity ratio, this research seeks to enhance our understanding of rotor dynamics and efficiency. Two-, three-, four-, and five-bladed rotors were designed and manufactured to have the same solidity ratio. This leads to smaller chord distribution values for higher blade numbers. The experimental analysis aims to quantify the effects of the number of blades and provides a comparative analysis of performance differences between the two rotor configurations (shrouded and open). For the open rotor, results indicate that increasing the number of blades has a minimal impact on overall performance. This is due to the decrease in the tip loss factor being counterbalanced by a decline in efficiency caused by the two-dimensional airfoil performance, which results from a smaller chord and a lower Reynolds number. In contrast, the shrouded rotor exhibits a noticeable performance decay with an increased blade count. Since tip loss is inherently absent in shrouded designs, the decline is primarily attributed to the two-dimensional airfoil performance. This decay occurs while maintaining a constant solidity ratio, highlighting the significant effect of blade count on shrouded rotor efficiency, thereby contributing to the optimization of rotor design in various engineering applications. [ABSTRACT FROM AUTHOR]

The controllable speed casing is a novel casing treatment approach that makes partial casing rotate at adjustable and proper speed to achieve stability expansion. Structural parameters of casing treatment are found to influence the effect of stability expansion by many studies. In this paper, the effect of the ending position of the rotatable ring in controllable speed casing on the tip leakage flow and the stability expansion was studied numerically. The results show that when the rotatable ring rotates at 30 % and 50 % rotor design speed, the controllable speed casing achieves the stability expansion of the compressor rotor no matter where the ending position is. The upstream movement of the ending position decreases the axial pressure gradient in the middle and rear of the tip passage. It pushes the shock wave downstream, which reduces blockage region at tip leading edge. The upstream movement of the ending position contributes to an approximately linear increase in the stable operating margin. [ABSTRACT FROM AUTHOR]