The present paper numerically conducted full-annulus investigation on the effects of circumferential total pressure inlet distortion on the performance and flow field of the axial transonic counter-rotating compressor. Results reveal that the inlet distortion both deteriorates the performance of the upstream and downstream rotors resulting in reduction of total pressure ratio, efficiency and stall margin of the transonic contra-rotating compressor. Regarding the development of distortion inside compressor, the downstream rotor reinforces the air-flow mixing effects and, thus, attenuates the distortion intensity significantly. Under the distorted inflow conditions, the detached shockwave at the leading edge of downstream rotor interacts with the tip leakage flow and causes the blockage of the blades passage, which is one important reason for the transonic contra-rotating compressor stall.

This work numerically investigates the importance of controlling the wake of upstream body in the tandem cylinders aiming at aerodynamics noise reduction. The two-dimensional unsteady Reynolds-averaged Navier–Stokes approach with the k–ω turbulence model and Ffowcs Williams–Hawkings method are employed to simulate the flow field and the aerodynamics noise, respectively. The flow in the porous media is calculated by a volume-averaged model. Analogy to the mass-spring-damper system, one preliminary model is proposed to reveal the key role of stabilizing the upstream body wake. The simulations of different porous materials coating designs are implemented to corroborate the model and provide more details of flow modification by porous materials coating. Results indicate that the porous materials coating designed on the upstream cylinder can decrease the wake impingement on the downstream cylinder via suppressing the vortex shedding. Subsequently, not only the tonal noise but also the broadband noise level of tandem system can be reduced. It is also clarified that the effects of downstream cylinder absorption and downstream cylinder wake control by porous materials coating is not comparable with the upstream cylinder wake control. The present study gives a new idea to flow control and noise reduction of the multibody systems considering efficiency and economy.

Large eddy simulation (LES) with Ffowcs Williams and Hawkings (FW-H) analogy is performed to investigate the flow structure and noise emission of NACA 65(12)-10 aerofoil with and without a serrated trailing-edge at a moderate Reynolds number (${\mathrm{R}}_{\mathrm{ec}}=5\times {10}^5$ ). Following, the noise reduction mechanisms and the noise source regions are analyzed in detail. Results indicate that trailing-edge serrations reduce the overall sound pressure level by up to 6 dB at a 0° direction angle, and the noise reduction mainly occurs at a frequency lower than 10 kHz. The trailing-edge serrations can act as vortex generators and, thus, reorganize the vortex structure, altering the spanwise vortex to a large-scale streamwise vortex. Besides, serrations reduce the magnitude and modify the distribution of the power spectrum density of pressure fluctuation in the near wake, and the spanwise coherence magnitude is decreased. Additionally, the phase interference of acoustic sources at different spanwise positions is enhanced. Wavelet analysis reveals that the hump of the broadband noise spectrum of the serration aerofoil is mainly contributed by the serration tip region. The conclusion provides inspiration for further noise reduction by trailing-edge serrations.