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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.

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.

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.

To study the influence of inlet turbulence on the prediction of flow structure in practical aeroengine combustor, large eddy simulation with dynamic Smagorinsky subgrid model is used to explore the complex unsteady flow field in a single burner of a typical aeroengine combustor with two-stage counter-rotating swirler. The complex geometric configuration including all film cooling holes is fully simulated without any conventional simplification in order to reduce the modeling errors. First, unsteady process that flow developing from static to statistically stationary state is fully simulated under laminar inlet condition to obtain a fundamental understanding of flow characteristics in the combustor. Afterwards, synthetic eddy method is utilized to generate a turbulent inlet condition so that a perturbation with about 5% turbulence intensity is superimposed to the inlet plane. Simulation result shows that for the laminar inflow case, flow separation occurs in the near-wall region of the diffusion section, inducing a boundary layer transition and consequently introducing turbulence with nonuniformity in space before the swirler. In contrast, synthesized inflow generated under turbulent inlet condition by synthetic eddy method is more spatially homogeneous. Time-averaged flow field inside the swirler cup reveals that turbulent inflow ultimately causes the swirling flow with higher rotating speed in central region and more uniform distribution along the circumferential direction. It also enhances the transverse jet flow from primary holes and reverse flow in the central recirculation zone, and makes streamlines corresponding to the recirculation vortices more symmetrical on central profile. Maximum recirculating velocity predicted in central recirculation zone is −27.65 m/s and −17.86 m/s in turbulent and laminar case respectively, and corresponding total pressure recovery coefficient is 96.03% and 96.81%.

This paper presents the studies performed to better understand the effects of increased tip clearance size on the unsteady flow behaviors and overall performance under the rotor–rotor interaction environment in a counter-rotating axial flow compressor. The investigation method is based on the three-dimensional unsteady Reynolds-averaged Navier–Stokes simulations. The results show that the intensified tip leakage flow in front rotor (R1) caused by the increased tip clearance size will lead to the growth of incoming incidence angle near the tip of the rear rotor (R2). The increasing of double leakage flow range plays a significant role in the sensitivity of the efficiency to tip clearance size and its extent is enlarged gradually with the increase of tip clearance size. As the tip clearance size is increased to 1.5τ (τ represents the designed tip clearance size) from 0.5τ, the results of the fast Fourier transform for the static pressure near blade tip show that two other new fluctuating frequency components appear due to the happening of tip leakage flow self-unsteadiness in R1 and R2, respectively. Additionally, the fluctuating strength near the tip in R2 is significantly increased. However, both the overall fluctuation in R1 caused by the potential effect from downstream and the oscillation in the hub corner on the pressure side of R2 are decreased obviously. The relative inflow angle tends to increase when the incoming wakes and tip leakage flow from R1 encounter the blade leading edge of R2, which leads to the result that the trajectory of tip leakage flow is shifted more upstream.

Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.

The profile designs of screw elements are very crucial to improving the mixing performance for the intermeshing counter-rotating twin-screw kneader. In order to find the inherent law among different profiles of screw elements and to derive a mathematical model which evolves different types of end cross-section profiles of screw elements, a universal mathematical model of end cross-section profiles of screw elements is presented in this work. Different types of profiles of screw elements, including those traditionally used can be obtained by evolutionary design method after changing the tooth number of female and male elements and other design parameters. Several typical screw elements with different types of end cross-section profiles are selected to analyze the mixing performance. Spatial flow patterns in flow channel of the screw elements are presented with particle tracking analysis by using mesh superposition technology. The mixing performance of different screw elements including distributive and dispersive mixing, contrastive analysis for some parameters, such as residence time distribution density function, segregation scale, rate of stretching, rate of shear, etc. are proposed. The results in this paper provide a data basis for the profiles selection of screw element for intermeshing counter-rotating twin-screw kneader.

A hybrid method combining a three-dimensional unsteady Reynolds-Averaged Navier–Stokes simulation of a cropped Counter-Rotating Open Rotors at approach conditions and an acoustic analogy either based on a time formulation, an advanced-time formulation of Ffowcs-Williams and Hawkings’ analogy, or on a frequency formulation, an extension of Hanson’s model to non compact chord length, has shown three main sources, the impacts of the front-rotor wakes on the aft-rotor, of the front-rotor tip vortex on the aft-rotor tip, and of the front-rotor hub horse-shoe vortex on the aft-rotor blade foot. Consequently, this study confirms that the aft-rotor is the dominant tonal noise source and has identified another potential noise source when the Counter-Rotating Open Rotors is installed caused by the strong tip vortex of the highly loaded cropped aft-rotor. The present rotor–rotor distance should not be reduced as the potential effect from the aft rotor is already felt on the front rotor. The influence of several numerical parameters including grid refinement, data sampling, and simulation length has been evaluated on both aerodynamic and acoustic performances.

Unsteady numerical simulations of a counter-rotating axial compressor are performed to investigate the unsteady effects of rotor–rotor interaction process and the tip flow unsteady behavior near the stall operating condition. The results show that potential effects from the rear rotor have a more pronounced influence on the front rotor. Because of the interaction between the two rotors and the unsteady flow behaviors, the strongest fluctuant regions are different for the two rotors. Additionally, the oscillation on the pressure side is generally much stronger than that on the suction side. Frequency analyses show that self-unsteadiness occurs with the frequency of 0.76 blade passing frequency due to the impingement of the tip leakage flow on the pressure side near leading edge of the adjacent blade. An interesting phenomenon, i.e., the emergence of a local high pressure spot, is observed in the tip region. As a whole, it is concluded that there are two key effects of the emergence of the local high pressure zone in the tip region: (a) more leading edge spillage of tip leakage flow and increasing the risk to trigger stall; and (b) a decrease in blockage associated with double-leakage of tip clearance flow within the influenced region of the local high pressure zone.

Yarn traversing with counter rotating blades is a well-established method of traversing the yarn, employed on several commercial winding machines. This method is mainly suitable for shorter traverse strokes and does not have positive control on yarn during traversing (especially at traverse extremes) as compared to other traversing systems. Moreover, yarn may be subjected to greater abrasion with traversing elements. This may lead to deficiencies such as lack of precision in yarn lay during package build-up that may be reflected in terms of poor package appearance. In this study, the blade profile of the existing yarn traversing mechanism employed on an assembly precision winder has been modified. Three modified blade profiles have been developed with the intention of improving control over yarn during traversing as well as at yarn transfer at traverse extremes from one blade to the other. Packages were built successfully with modified blade profiles. This paper summarizes developmental work of improving profiles of the original design of counter rotating blades to achieve the aforementioned intentions.

Based on the preliminary validation of the numerical results with an experiment, the steady results of different tip clearance size effects on the performance and tip leakage vortex of counter-rotating compressor were discussed. The predicted results showed that the stable margin and isentropic efficiency of the counter-rotating compressor decreased with increasing of the tip clearance size. Furthermore, increasing the tip clearance size had a greater negative effect on the performance of the upstream rotor than the downstream rotor. Detailed flow field analyses further demonstrated that the unstable flow occurred in the two counter-rotating rotors with greater tip clearance size. The rotor downstream was the main unstable factor which caused the counter-rotating compressor to breakdown when a smaller tip clearance size was used.

In this article, the nonlinear harmonic method implemented in Fine/Turbo code has been evaluated for unsteady rotor–rotor interaction analysis. Strengths and weaknesses of the nonlinear harmonic method are highlighted through direct comparison with experimental data and time-domain unsteady simulation for the Northwestern Polytechnical University counter-rotating research compressor at the design and off-design conditions. The rotor–rotor interactions were studied in detail to advance the understanding of the flow physics involved. Based on the unsteady simulation, deterministic stresses were computed and compared to the nonlinear harmonic method to analyze distinct sources of unsteadiness and their effect on the time-averaged flow field. For the present case, the nonlinear harmonic method efficiently computes unsteady flows and shows major improvements regarding the computational time (to a factor up to 10).

In view of the counter rotating field theory, can a single phase stator winding be used to drive two rotors simultaneously at different speeds in opposite directions, and if so how does the machine perform? The paper puts forward some experimental and theoretical answers to these questions.

Erosion test in a model counter-rotating radial flow turbine has been performed to assist in the design of a 460-MW radial flow turbine. Three rows of erosion specimens were inserted at different radial locations in the last blade ring upstream of the blades to investigate the influence of the radial distance between the stages. Results showed that small droplets were formed and that erosion diminished with increased radial spacing up to a certain distance. A theoretical model for calculating droplet trajectories, sizes, and impact velocities has been derived, taking full account of wake velocity, variable droplet drag coefficient, and atomization. The calculations explained all the experimental facts and made it possible to convert the model test results to the full-size turbine showing no risk of erosion in the latter.