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Several ten-stages-compressor of a high bypass ratio turbofan engine was used as the research object, the change law of tip clearance and its effects on aerodynamic performance and stable boundary of the compressor were investigated based on a high speed compressor component, core engine and complete engine test facility. The mechanism and the sensitive area of tip clearance effect on the overall performance and each stage performance of multistage compressors was revealed by detailed simulation results of transonic and subsonic stage performance. The results show that the clearance change law of compressors of different sizes is consistent, which is mainly related to centrifugal force and temperature filed. Flow-pressure ratio and flow-efficiency characteristics of the compressor at design rotational speed Indicate a feature of whole reduction while the clearance increases, and the clearance has more impact on the back subsonic stage. With the increase of the tip clearance, the efficiency of the front transonic stages of the compressor does not decrease for the small ratio of clearance to the big blade height, but the work capacity of the back subsonic stage decreases obviously, and the influence of the clearance mainly concentrates on the back subsonic stage, which makes the compressor efficiency and stall margin droop. [ABSTRACT FROM AUTHOR]

Tracer pathline statistics have rarely, if at all, been used in the investigation of compressible subsonic, transonic and supersonic flows past a circular cylinder. Here, we report pathline histogram, conditional histogram and zonal histogram data, focusing on the characteristics of particle instantaneous flow reversal and their dependencies on Mach number and tracer release position. The far-upstream Mach number and the diameter-based Reynolds number used for these three flow regimes are $ ({0.2, 10000}), ({0.9, 3900}) $ (0.2 , 10000) , (0.9 , 3900) and $ ({1.2, 10000}) $ (1.2 , 10000) , respectively. The subsonic surface-release histogram profiles display unexpected persistent oscillations at a frequency $ 50 $ 50 times of the periodic vortex shedding frequency, reflecting the effect of a very small magnitude zig-zagging type of particle motion in a region very close to the wall and slightly behind the mean flow separation location. No similar high-frequency oscillation is observed in the corresponding transonic and supersonic histograms likely because, at $ \textrm{Ma} \ge 0.9 $ Ma ≥ 0.9 , periodic vortex shedding ceases to exist and the near-wake becomes a quasi-laminar recirculation zone bounded by a pair of converging slip-layers with a neck opening to the far-wake. At the instant of $ 5 $ 5 subsonic vortex-shedding periods after being released from the cylinder surface, there are $ 1.67\% $ 1.67 % , $ 35.2\% $ 35.2 % and $ 39.7\% $ 39.7 % particles that experience flow reversal in the subsonic, transonic and supersonic flows, respectively. Surprisingly, in the present transonic flow, growth of the turbulent far-wake behind the pair of lambda-shocks is constrained over a considerable streamwise distance. [ABSTRACT FROM AUTHOR]

The purpose of this study is to analyze the subsonic and transonic water entry of the axisymmetric body with compressibility effect considered. The water-entry processes of axisymmetric body are numerically investigated, with Tait state equation and energy equation used to describe the compressibility of the liquid. Reasonable agreement has been obtained between the numerical results and the experimental measurements of trajectory, velocity and acceleration. The cavity evolution and dynamic characteristics of subsonic cases are investigated for vertical and oblique water-entry. The results show that the maximum drag coefficient of the oblique water entry is lower, and it is affected by a large moment which causes pitch angle and trajectory inclination angle to change significantly. In the oblique transonic conditions, the effect of compressibility of the liquid on the dynamic flow characteristics is analyzed. On this basis, the influence of entry angle on the hydrodynamic characteristics is investigated. It is concluded that the water-entry angle has a more significant influence on the trajectory characteristics. • Investigate the flow structure and dynamic characteristics of subsonic water-entry cases for vertical and oblique water-entry. • Analyze the effect of compressibility of the liquid on the dynamic flow characteristics of transonic water-entry cases. • Improve the understanding of the influence of entry angle on the hydrodynamic characteristics with compressibility considered. [ABSTRACT FROM AUTHOR]

The objective of this paper is to address the simulation of supercavitating flows around a slender body projectile at the sub-, trans- and supersonic speeds with the water compressibility effects considered. Based on the slender body theory (SBT) and the matched asymptotic expansion method (MAEM), the integro-differential equations for the cases of M a <1 and M a >1 are derived and solved. The results show that there is a good agreement of the supercavity shape for both the cases of M a <1 and M a >1 between the numerical simulation and the experimental results. The influence of Mach number on the supercavity length L , maximum radius R , slenderness λ , the corresponding growth rate of the supercavity length L ˜ , the growth rate of the maximum supercavity radius R ˜ , and the position of the supercavity maximum section (PSMS) are discussed. It can be found that L ˜ is much bigger than R ˜ , due to the large λ . It also concludes that the front part of the supercavity is thicker than the rear part, and the PSMS moves forward further at supersonic speed. Finally, the reason for the supercavity shape transition around M a = 1 is illustrated and it may be the c a use of the extension of perturbation zones at transonic speed. [ABSTRACT FROM AUTHOR]

The flow past open cavities is a problem that is encountered in many engineering applications and can result in intense acoustic tones. The flow physics and acoustics of cavity configurations are complex and computational simulation techniques provide an opportunity to gain further understanding and provide a tool to predict not only cavity tone frequencies but their amplitude. In this paper, we describe the available techniques for performing computational aeroacoustic simulations of cavity flows, and review recent applications for the prediction and control of cavity tones in subsonic, transonic and supersonic regimes. [ABSTRACT FROM AUTHOR]