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Because of their potential to reduce aircraft emissions, counter-rotating open rotors (CRORs) have seen a renewed interest in applications, from civil aviation to urban air mobility. However, there...

Pylons are commonly used for the mounting of engines in the aircraft industry. On the other hand, the installation of a pylon influences the noise generation mechanisms and therefore alters the broadband noise characteristics of a given turbomachinery setup. In this investigation, a counter-rotating open rotor with and without a pylon is investigated in order to determine its effects on broadband noise sources. The various broadband noise sources and their typical frequency ranges have been determined using beamforming maps and spectral analysis. In order to attain a clear impression regarding the broadband noise sources, the Double Filtering beamforming method has been utilized in the investigation. This method removes the tonal components from the recorded signal of a microphone array, resulting in a purely broadband signal. Using beamforming maps, the dominant broadband noise source amplitudes and locations can therefore be investigated in great detail. Compared to other methods, the investigation of measurement data and beamforming maps helps determine the amplitude, the frequency range, and the significance of the various types of broadband noise sources that are truly present in the emitted noise. It has been found for lower frequencies, that the broadband noise sources at the blade root of the aft rotor are dominant, while for higher frequencies, the significant broadband noise sources are localized to the trailing edge region of the forward rotor and the leading edge of the aft rotor. The installation of a pylon has resulted in an additional broadband noise source appearing at the blade tip of the aft rotor.

Based on two cases of the double impellers on different shafts in the co-rotating and counter-rotating, the distribution of the velocity, streamline, turbulent kinetic energy, and turbulent energy dissipation rate are obtained through three-dimensional unsteady numerical simulation. Very good agreements between experimental and numerical results have been obtained. The hydrometallurgy purification experimental platform was built with the size of one third of the simulated. The results show that the mechanical string mixing system with double impellers on different shafts can form a more obvious convection effect in the central area of the double impellers, which can effectively break the mixing isolation region and improve the mixing effect. In the co-rotating case, the two impellers can generate strong convection in the central area and form an interactive vortex and a high-speed flow channel between the two impellers. while the convection formed by counter-rotating case is weaker and the vortex structures are independent of each other. The counter-rotating system performs better in the macro momentum transfer and the co-rotating system performs better in the micro-mixing level. In the experiments of hydrometallurgy purification, 7.93% more energy is used in the co-rotating system than that of the counter-rotating system. The average energy consumed by co-rotating in the process of purifying every one percent of Cd2+ ions are 8.65% lower than that of counter-rotating. The co-rotating system can improve microscopic mass transfer effect and finally save energy and time compared to the counter-rotating system.

Purpose This paper aims to analyze the temperature field and the heat transfer performance of the counter rotating dual rotor bearings (CRDRB) based on the air phase flow field at different speeds to provide effective support for the lubrication and the thermal design of CRDRB. Design/methodology/approach In this study, taking H7006C angular contact ball bearing as an example, based on the flow visualization technique and the thermal analysis methods, the effects of outer ring speed on the air phase flow field, the temperature field and the heat transfer in bearing cavity were investigated. Findings Results indicated that there were more complex turbulent air vortices in CRDRB cavity. Turbulent cyclones in critical contact zone reduced the heat dissipation capacity of air. Compared with single rotor bearing with a static outer ring, the average heat transfer coefficient reduced by 11.78% and the average temperature raised by 3.06 K inside CRDRB cavity. Under the influence of outer ring rotation, the high temperature area in ball-inner raceway contact zone and pocket raised and reduced by 160.13% and 30.48%, respectively. The outer ring rotation had opposite effect on the heat dissipation of raceway contact zone and pocket. Originality/value The air phase flow field characteristics and the heat transfer performance of CRDRB were revealed and analyzed from the mechanism. An area quantification method was presented as an auxiliary mean of the thermal analysis to evaluate the heat transfer performance of bearing.

The propeller is the primary component of flying vehicles powered by electric motors, internal combustion engines, and turboprops for producing thrust. A propeller thrust is produced in the engine by effective spinning of the propeller through air for cost-effective and environmental friendly flight. Natural flyers like birds as well as aquatic animals like humpback whales effectively use its wings and flippers with its surface features for capturing its prey and escaping from their enemies. As part of this work, corrugations are established in the leading edges or in the suction surfaces of the propeller to modify the flow field prevailing over there. Because of the flow field, the surface corrugations or leading edge corrugations energize the boundary layer in the surfaces of the propeller by counter-rotating vortices which, in turn, delays the separation of the boundary layer from the surface. The performance parameters of the propeller such as thrust, torque, propeller efficiency, power consumption etc., are measured using propeller test rig. Depending on the location of surface or leading corrugations, the variations in the performance of the propeller are investigated for further optimization on the selection of better propeller to the applications of UAVs operating at low Reynolds No.

A new dynamical model with five rigid frames (RFs), driven by two counter-rotating exciters, is proposed to explore the synchronization, stability, and motion characteristics of the system in this paper. The motion differential equations and the corresponding responses of the system are given firstly. Using the average method, the average torque balance equations for the two exciters are deduced. According to the relationship between the difference of the dimensionless effective output electromagnetic torques for the two motors and the coupling torques of the system, the theory condition of realizing synchronization is obtained. Based on the Hamilton’s theory, the theory condition of stability of the system is deduced. The stability and motion characteristics of the system for different resonant regions are qualitatively discussed in numeric, including the stable phase difference of the two exciters, relative phase relationships among the five rigid frames, amplitude-frequency characteristics, stability coefficients, and the effective load torque between the two exciters. Simulations are carried out to further quantitatively validate the feasibility of the above theoretical and numerical qualitative results. It is shown that in engineering the reasonable working points of the system should be selected in Region II, only in this way, can the synchronous and stable relative linear motion of the system with the zero stable phase difference in vertical direction be realized, and in this case, the vibrations of the four inner rigid frames (IRFs) in the horizontal direction are compensated with each other, and the energy is also saved due to utilizing the resonant effect. Based on the present work, some new types of vibrating coolers/dryers or vibrating screening machines can be designed.

The sealing of the rotor-rotor gap and rotor disk cooling are vital to the safe operation of the vaneless counter-rotating turbine(VCRT). In order to quantifies the influence of the wheel-space cavity flow on the VCRT aerodynamic performance, and to improve turbine efficiency of the VCRT at certain rim seal ejection rates, numerical studies which considered the effects of rotor-rotor rim seal flow ejection are carried out in this paper. The three dimensional unsteady computational fluid dynamic analysis of a VCRT at the engine conditions are performed, and the seal flow ejected downstream of the high pressure rotor row at six sealing flow rate are modeled. The interaction among the high pressure rotor trailing shock wave, the downstream secondary flow and the seal flow has been studied and quantitatively characterized as a function of the purge ejection rate. Numerical results show that seal flow- mainstream flow interaction is entirely dominated by the high pressure rotor trailing edge shock at the hub, low pressure hub passage vortex and the mixing of the sealing flow from wheelspace and mainstream. When the mass flow rate of the coolant is smaller than some threshold value, the shock loss of the high pressure rotor and hub secondary flow loss of the low pressure rotor are decreased with the increasing of the coolant mass flow rate. It causes that the VCRT efficiency is gradually increased. On condition that the amount of the seal flows is beyond the threshold value, the key roles in modification of the VCRT performance are changed. The increment of the hub secondary flow loss and the mixing loss are gradually larger than the decrement of the shock loss. As a result, the turbine efficiency gradually decreases.

Present numerical investigation proposes to mitigate the effects of Counter rotating vortex pair (CRVP) by employing a pair of vortex generator. Numerical simulation has been carried out to investigate the effect of placement of vortex generator on the characteristics of film cooling effectiveness. Various configuration has been taken based on vortex generator location at upstream, downstream of circular film cooling hole. Along with these utilizing multiple vortex generator at different downstream location also has been detected. The jet to cross flow blowing ratios ( M = ρ juj/ ρ cfucf) is maintained at unity while Reynolds number based on free stream velocity and film cooling hole dimension is kept at 17,000. The investigation of suitable turbulence model has been studied. The results are compared with baseline case. The numerical investigation is accomplished implementing FLUENT commercial code adopting the K-omega SST model. Among configuration E and all quantity (Density ratio ( DR), Blowing ratio ( M), Reynolds number (Re) and Turbulence intensity ( TI)) better CRVP distribution is depicted for TI and lowest for configuration E.

The aerodynamic characteristics of three types of six-bladed main rotors are calculated on the basis of the nonlinear free vortex wake model. The vortex wake shapes and induced velocity fields in the rotors jet are analyzed. The figure of merit (FoM) diagrams are received.

Owing to the existence of the cone angle, the size of a conical counter-rotating twin screw continuously changes along the axis, so it is not easy to model using SolidWorks. In this study, the parametric design of the modeling process is completed based on the Visual Basic language and a program-driven method. Finally, the SolidWorks program plug-in and user interface are developed to complete the automatic generation of the three-dimensional model of a conical counter-rotating twin screw.

This work presents a new control strategy for counter-rotating wind turbine (CRWT) driven doubly-fed induction generator (DFIG) under grid disturbances, such as unbalanced network voltage scenarios. The proposed strategy based on the power control used dynamic gains second order sliding mode control (SOSMC). The power control of a DFIG by SOSMC widely based on the super-twisting (ST) algorithm with invariable parameters and sign functions. The proposed control method consists in using dynamic-parameters ST algorithm that ensures a better result than a conventional strategy. The proposed control scheme used 2 sliding surfaces such as reactive and active powers to control them. Also, the sign functions are replaced by saturation (sat) functions in order to minimize the chattering problems. Simulation results depicted in this research article have confirmed the good usefulness and effectiveness of the proposed adaptive super-twisting algorithm of the CRWT system during grid disturbances.

In this work, a visualization of supersonic counter-rotating vortices pair is performed using the methods of maximum vorticity and the λ2-criterion. Numerical data were obtained on the supercomputer system K-60 at the KIAM RAS using a parallel algorithm for modeling of turbulent flows.

In this paper, a new configuration is proposed for using Savonius rotors by installing two Counter-Rotating Savonius Rotors (CRSR) together. In order to study the aerodynamic performance of the CRSR turbine, 2D unsteady turbulent flow around the CRSR turbine is simulated using commercial CFD software ANSYS-Fluent16.0. Turbulence modeling is done using $$k - \omega$$ SST model. Numerical results demonstrate a considerable improvement in aerodynamic performance of the CRSR turbine in comparison to a single conventional rotor. Effect of the distance between two rotors and different angular positions of two rotors on the CRSR turbine performance is studied. It is shown that the most effective parameter influencing the performance of the CRSR turbine is the distance between the rotors. Numerical results reveal that, locating two rotors in an optimal phase angle (θ = 90) and distance(S = 1.0D0), average power coefficient of the CRSR turbine can be increased to 21%, which indicates a rise of 38% compared to conventional Savonius rotors.

The vector control (VC) method based on proportional-integral (PI) controllers of a doubly fed induction generator (DFIG) integrated in a counter rotating wind turbine (CRWT) system have many problems, such as low dynamic performances, coupling effect between the d-q axes and weak robustness against variation parametric. In order to resolve these problems, this research work proposes an adaptive backstepping sliding mode (ABSM) controller. The proposed control strategy consists in using dynamic-gains that ensures a better result than a conventional VC method. Stability of the proposed ABSM control approach has been proved by the Lyapunov method. Simulation results depicted in this research paper have confirmed the good usefulness and effectiveness of the proposed ABSM control.

Helicopter engines are often mounted atop the fuselage to keep the aircraft footprint small and optimal for operations. As a result, hot gases produced by the engines may inadvertently impinge upon the tail boom or dissipate inefficiently that compromises on operation safety. In this study, a scaled fuselage model with a hot air blower was used to simulate hot exhaust gases. The velocity field immediately outside the exhaust port was measured through stereoscopic particle image velocimetry to capture the trajectory and flow behaviour of the gases. Two cases were considered: freestream to exhaust velocity ratios of 0 (no freestream velocity) and 0.46 (co-flowing free stream), respectively. The formation of a counter-rotating vortex pair was detected for both cases but were opposite in the rotational sense. For the case without freestream, the plume formed into a small “kidney” shape, before expanding and dissipating downstream. For the case with freestream, the plume formed into a slenderer and more elongated “reversed-C” shape as compared to the case without freestream. It also retained its shape further downstream and maintained its relative position. These observations on the trajectory and shape of plume provide basis to understanding the nature and interaction of the plume with its surroundings. Accepted version This work was supported by Leonardo-Finmeccanica Helicopter division.

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

We present a new scenario for the origin of the counter-rotating stars in disc galaxies, defined as stars that have a negative tangential velocity. This scenario involves a merger between two gas-rich disc galaxies that have comparable masses, are nearly coplanar, and are rotating in the same direction. The merger results in an intense starburst, during which a significant fraction of the gas is converted to stars. The system then settles into an equilibrium configuration consisting of a thick disc and a bulge partly supported by velocity dispersion and a thin disc supported by rotation. Star formation proceeds until most of the gas supply is exhausted. Stars formed during the starburst have tangential velocities ranging from $-600$ to $600\, {\rm km\, s^{-1}}$. Stars formed afterward in the thick disc and bulge have high eccentricities and low tangential velocities, typically in the range $-100$ to $100\, {\rm km\, s^{-1}}$, while stars formed in the thin disc have large, positive velocities. All fast, counter-rotating stars ($V\lt -200\, {\rm km\, s^{-1}}$) are old, metal-poor, with very low dispersion in ages and metallicities. By contrast, fast, corotating stars ($V\gt 200\, {\rm km\, s^{-1}}$) have a wide range of ages and metallicities. The average abundances ratios $\rm [O/H]$ and [Fe/H] for fast, corotating stars typically exceed the corresponding ratios for fast, counter-rotating stars by $0.1-0.4\,\mathrm{ dex}$, while the dispersion in the values of NFe/NH are larger by factors between 2 and 14. This provides an observational signature of major, gas-rich mergers at high redshift.

Existing methods of improving the performance of mine counter‐rotating fans (MCRFs) through speed matching of the rotors have certain drawbacks. This study proposes a variable‐speed method for the two rotors of an MCRF to improve its performance, including the blocking margin, operational safety, high‐efficiency working range (HER), and stability margin. Experimental and numerical methods were used to study the pneumatic performance of the MCRF. The results show that the second rotor (R2) is the critical stage affecting the safety of the motor, HER, and blocking margin. A condition‐adaptive speed matching method was proposed for R2 to avoid overloading the second motor at low‐flow rates and to improve the blocking margin and HER. The first rotor (R1) is the critical stage determining the stability margin of the MCRF. Reducing n1 and increasing n2 at low‐flow rates helped extend the stability margin.

The objective of this study is to investigate the flow performance analysis for an electric fan with counter-rotating fan. The counter-rotating fan is a device with the method of mutually rotating two moving blades in an opposite direction. It is possible to increase the pressure between fans even with a narrow diameter of a housing and to blow wind over long distances. Because of these advantages, we are developing an electric fan with counter-rotating fan that has the function of an air purifier by installing a filter on the rear. In this paper, the flow characteristic and performance of the counter-rotating fan are clarified by the computational fluid dynamics results according to the change of the blade angle and rotational speed ratio.

Flow in a Counter Rotating Turbine (CRT) stage is composite and three dimensional due to the blade geometry of nozzle, rotor 1 and rotor 2 that are twisted along the span, spacing between them, tip clearance provided on rotors and also because of oppositely rotating rotors. Present work analyzes the flow field through the nozzle and rotors at planes taken at various axial chord distances. Blade-to-blade contours and the hub-to-tip plots reveal the actual scenario of flow in the turbine stage. Nozzle and the two rotors are modeled in case of the CRT configuration. Boundary conditions are specified as pressure at inlet of the nozzle and flow rate at the outlet of rotor 2. Total pressure, velocity, entropy and TKE distribution through the blades are used to identify the flow over CRT. Flow through the blade rows is distinguished by effects of boundary layer, secondary flows near the hub, pressure gradient effects, presence of vortical flow structures in the passage and near the tip. Total pressure distribution near the midspan in case of nozzle and rotors show the presence of boundary layers and wake regions. Entropy and TKE contours show the loss regions in all the blade rows. Flow losses are more in rotor 2 than rotor 1. Secondary velocity vectors show the presence of vortex regions in the passage and tip clearance. Blade-to-blade contours of CRT reveal the actual flow scenario surrounding the blades. Hub-to-tip plots show the variations of flow parameters while moving from the bottom to top most position of blade. Thus, the present work identifies the exact flow structure in a counter rotating turbine and paves the way for researchers to negotiate flow losses and improve the CRT performance further.

Flow around a pair of cylinders is of interest for various applications. Especially with the development of self-propelled, autonomous vehicles, this topic has gained further importance. There have been experimental, numerical and, to a much less extent, theoretical studies of this flow and its implications on the cylinders. However, the complexity of the problem does not allow a general solution, and case-by-case solutions have been produced. In this study, a theoretical approach was embraced, in which differential geometry is employed to model the local flow between a pair of counter-rotating cylinders. In order to obtain practical formulae for a steady, laminar, incompressible flow, Navier-Stokes equations were simplified and expressed in a new, parabolic coordinate system. Then, further simplifications due to the symmetrical nature of the problem were applied. Finally, boundary conditions were imposed while performing the integrals, and the desired equations for velocity and pressure were reached. Unlike the previous studies that are limited to very slow flows, the equations obtained in this study are applicable in the entire incompressible, laminar regime, albeit only between the cylinders. Using these equations, the effects of the rotation speed, cylinder spacing and cylinder radius were studied and presented graphically.

The present work investigates the coupling synchronization principle and stability in a vibrating system with two pairs counter-rotating unbalanced rotors (also called exciters). Based on Lagrange equations, the dimensionless coupling differential equations of motion of the system are deduced. The synchronization criterion of two pairs exciters stems from the averaging method, it satisfies the fact that the absolute value of dimensionless residual torque difference between arbitrary two driving motors is less than or equal to the maximum of their dimensionless coupling torques. The stability criterion of the synchronous states complies with Routh-Hurwitz principle. The coupling dynamic characteristics of the system are numerically analyzed in detail, including synchronization and stability ability, maximum of the coupling torque and phase relationship, etc. Some simulation results applying the Runge-Kutta algorithm are performed, it is shown that the motion states of the system can be classified into two types: sub-resonant state and super-resonant state. Generally in engineering, the ideal working points should be selected in sub-resonance region, in this case the expended energy can be saved relatively by 1/5–1/3, which is less than that in super-resonance region under the precondition of the same vibration amplitude value.

General energy demand is continuously increasing due to the fact that wind turbines and other renewable energy sources have begun to appear in previously unexplored areas, such as on the roofs of buildings. In view of this demand, a new type of wind turbines described in this article could become one of the energy generating tools in a smart grid system. In this article, first conventional and unconventional wind turbines are reviewed with respect to efficiency. Then a Counter Rotating Dual Rotor Wind Turbine (CO-DRWT) construction is analysed with Computational Fluid Dynamics (CFD) codes considering a fixed radial and a variable axial distance. In the analysis, power coefficients were calculated for different configurations. It was found that in case of the dual rotor wind turbine, the optimal axial distance for half diameter radial shift was in the range of 0,2 - 0,25 diameter.

Marine equipment generally lacks efficient power supply methods. The high energy density of wave energy can facilitate the converter miniaturization and make them easily integrated into marine equi...

The paper presents the results of computing aerodynamic properties of the CRTF2A counter-rotating cowled fan developed as part of the European VITAL program. To achieve these results, we used the following software packages: NUMECA FINE TURBO, ANSYS CFX and CIAMs own 3D--IMP--MULTI hydrocode. We use the RANS approach to model turbulent flows. We performed a three-dimensional computation, completing Reynolds-averaged Navier --- Stokes equations by various turbulence models for the following relative angular frequency modes: n = 1 and 0.9. We used the following turbulence models available in the software packages: k--ε (ANSYS CFX, 3D--IMP--MULTI), k--ε (ANSYS CFX, NUMECA FINE TURBO, 3D--IMP--MULTI), SST (NUMECA FINE TURBO, ANSYS CFX, 3D--IMP--MULTI). We plotted head characteristics for each software package and determined the main differences. We plotted adiabatic efficiency and total pressure ratios as functions of height for the first and second rotors at the maximum efficiency points for both modes in the ANSYS CFX, NUMECA FINE TURBO and 3D--IMP--MULTI software packages

The influence of a counter-rotating vortical gust pair is numerically investigated on a streamlined laminar flow and forced convection heat transfer around a steadily rotating two-dimensional circular cylinder. Reynolds number is kept to a fixed value of 100 based on cylinder diameter (D). The working fluid used is water having a fixed Prandtl number of 7. The non-dimensional rotation rate is altered within the vortex shedding regime i.e. 0≤α≤1.5 in the steps of 0.25. The numerical results were computed via commercially accessible CFD software package FLUENT®. The governing flow equations are continuity, momentum, and energy equations have been resolved via constant wall temperature (CWT) boundary condition. The numerical outcomes are computed illustrating the variation in the lift coefficient, Strouhal number, average and local Nusselt number, vorticity and temperature contours around the isothermal rotating cylinder. The influence of the vortical gust is observed to stretch the shear layer in a typical manner. The vortical gust can be treated as an additional heat transfer suppression technique in conjunction with rotation for a circular cylinder.

Counter-rotating turbomachines have the potential to be high efficiency, high power density devices. Comparisons between conventional and counter-rotating turbomachines in the literature make multiple and often contradicting conclusions about their relative performance. By adopting appropriate non-dimensional parameters, based on relative blade speed, the design space of conventional machines can be extended to include those with counter-rotation. This allows engineers familiar with conventional turbomachinery to transfer their experience to counter-rotating machines. By matching appropriate non-dimensional parameters the loss mechanisms directly affected by counter-rotation can be determined. A series of computational studies are performed to investigate the relative performance of conventional and counter-rotating turbines with the same non-dimensional design parameters. Each study targets a specific loss source, highlighting which phenomena are directly due to counter-rotation and which are solely due to blade design. The studies range from two-dimensional blade sections to three-dimensional finite radius stages. It is shown that, at hub-to-tip ratios approaching unity, with matched non-dimensional design parameters, the stage efficiency and work output are identical for both types of machine. However, a counter-rotating turbine in the study is shown to have an efficiency advantage over a conventional machine of up to 0.35 percentage points for a hub-to-tip ratio of 0.65. This is due to differences in absolute velocity producing different spanwise blade designs.

We have performed single-active-electron numerical calculations of neon- and argonlike atoms interacting with short, intense, circularly polarized laser pulses at wavelengths between 10 nm and 1000 nm. Our results reveal a surprisingly large change by a factor of about 100 in the ionization ratio of electrons in initial states counter-rotating with respect to the field over corotating electrons in the previously unexplored intermediate few-photon ionization regime. The physical mechanism behind this observation is related to resonant enhanced ionization via states close in energy to the initial states. These doorway states are accessible exclusively from the initial state for counter-rotating electrons within the respective wavelength regime. The results may open a new route for controlling the generation of spin-polarized electrons by ultrashort laser pulses.

Made available in DSpace on 2020-12-12T02:15:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Vibration isolation of a floating raft system typically found in a marine application is of concern in this paper. Housed on the raft are electrical motors each driving two counter rotating shafts with eccentric masses attached. An experimental study is described in which vibration transmitted to a large-scale, laboratory-based hull-like structure is attenuated by using three measures. They are, the use of vibration isolators between the raft and the hull-like structure, adjustment of the phase of the electrical supply between the motors to minimize vibration transmitted through the isolators, and the application of an active vibration control system using hydraulic actuators placed in parallel with the isolators. The results show that this combination of measures is extremely effective at reducing the vibration transmission to the hull-like structure, and consequent reduction the sound radiation. It is more effective than the application of any of the vibration control measures applied by themselves. Power and Energy Engineering College Harbin Engineering University Departamento de Engenharia Mecânica Universidade Estadual Paulista (UNESP) Ilha Solteira (SP) Departamento de Engenharia Mecânica Universidade Estadual Paulista (UNESP) Ilha Solteira (SP)

Helical structures continue to inspire, and there is considerable temptation to attribute helicity to columnar liquid crystals (LC). While short isohelical sequences are undoubtedly present, and longer ones in chiral or chiral-doped compounds, the order is only short-range, equivalent to a paramagnet without or with field. However, here we report a confirmed example of a true LC phase of achiral compounds consisting of columns, each being a long-range homochiral helix. Long-range periodicity and isochirality are maintained by intercolumnar interaction. This orthorhombic LC, spacegroup Fddd, is discovered in compounds with either bent or straight rod-like pi-conjugated cores. There are 4 right and 4 left-handed ribbons or star-profiled columns per unit cell. The structure is equivalent to an antiferromagnet with twist replacing spins. A theory based on interacting quadrupoles confirms this structure as energetically favoured over alternatives. The findings open a new approach to homochirality in achiral compounds, with promising optical/chiroptical properties.

The paper deals with the design optimization of the compressor stage with counter-rotating rotors, especially in order to create a model which, due to its parameters in real operation, would achieve the maximum possible values of efficiency. The primary goal of this work is to create a design of a compressor stage with counter-rotating rotors from a theoretical point of view. The compressor stage model is created using Inventor modelling software and the subsequent design evaluation and optimization is based on airflow analysis of the compressor stage using Ansys Discovery Live software. The secondary goal is to point out the existence and application of innovative and progressive technology of rapid prototyping in the world of aircraft component production and at the same time to emphasize its benefits in comparison with conventional production techniques applied in the initial stages of aircraft component production.

Turbomachinery with double counter-rotating impellers offer more degrees of freedom in the choice of design and control parameters compared to conventional machines. For these innovative machines, the literature review shows that more published works are available concerning axial type turbomachines than centrifugal ones. This work deals with a preliminary design and performance analysis applied to two counter-rotating impellers of a centrifugal compressor. We present here the design practice developed based on 0D/1D models, also coupled with optimization and stream-curvature through-flow methods to satisfy the selected design-criteria. An analyze of aerodynamic performances results are made and compared to those available experimental and numerical data of a baseline configuration, composed of one centrifugal-impeller and a volute. The compressor studied here includes a first conventional impeller with an axial inlet and a mixed or centrifugal outlet. The second impeller is designed parametrically and can be considered as a rotating-diffuser with a radial or mixed inlet and outlet. Ultimately, the numerical simulation results of a selection of candidate solutions are discussed.

Counter Rotating Open Rotors (CROR) have the potential to reduce environmental emissions thanks to their high propulsive efficiency. However, there are a number of concerns surrounding their acoustic emissions. This contribution presents a novel multi-configuration CROR that offers considerable noise reductions. In particular, we consider locking either fore or aft rotor during take-off, with the running rotor providing the required thrust. Duringcruise, both rotors are operated to retain the high efficiency of the CROR. A coupled Computational Fluid Dynamics-Computational Aeroacoustics analysis (CFD-CAA) has shown the potential of this multi-configuration concept to offer substantial noise reductions when compared to a baseline CROR. During a simulated constant-altitude flyover at take-off conditions, reductions of 3.5 dBA and 7.9 dBA have been demonstrated when either fore or aft row is locked, respectively. Using the EPNL metric, this result corresponded to7 EPNLdB and 12EPNLdB, respectively, for the same flyover.