We report work done to investigate the adaptability of the end wall unsteady pulsed jet (UPJ) at different incidence angles. In this research, the influence of the UPJ on the cascade aerodynamic performance at different incidence angles was systematically studied using validated numerical simulation methods. A comparative analysis using a traditional steady constant jet (SCJ) was also carried out. The numerical results show that the control effect of the UPJ is significantly superior to that of the SCJ for the design incidence angle, and the same for the time-averaged jet flow. When the time-averaged jet flow ratio ms = 0.28% and the actuation frequency F+ = 0.80, a maximum total-pressure-loss coefficient reduction of 28.66% and a static-pressure-rise coefficient increment of 13.17% are obtained. Compared with the SCJ, the loss for a cascade with the UPJ is decreased by 25.65%, and the static-pressure-rise coefficient is increased by 10.54%. For variable incidence angle, the UPJ can diminish the cascade loss for the range of incidence angle i from −8° to +4° and can improve the cascade aerodynamic performance to the greatest extent near i = 0°. The SCJ shows excellent adaptability when the incidence angle is negative, but worsens the cascade performance at large positive incidence angles.

The influence of the ratio of dimple depth-to-print diameter ($\lambda$) on the highly loaded compressor cascade NACA0065-K48 is investigated based on the Reynolds-averaged Navier–Stokes (RANS) method. Simulations are conducted with a validated shear-stress transportation (SST) turbulence model coupled with the Gamma-Theta ($\mathsf{\gamma }-{\mathrm{Re}}_{\mathsf{\theta }}$) transition model at the inlet Mach number of 0.7. At 5~25% of the axial chord on the suction surface, four rows of dimples are arranged in parallel, and the dimples’ spacing is 4 mm. Moreover, there are five kinds of $\lambda$, ranging from 0.125 to 0.875, which determine the pressed arc of a spherical dimple. Three flow regimes (diffuser–confuser flow, tornado-like vortex and horseshoe vortex) with the same topological structure are observed in these dimples, which affect the flow and performance of the cascade by changing the energy distribution. The distribution of turbulent kinetic energy (TKE) reflects the disturbance of the tornado-like vortex in the inferior arc dimples ($\lambda =0.375$) intensely, whereas the disturbance of the horseshoe vortex in superior arc dimples ($\lambda =0.625, 0.875$) is relatively weak. Numerical results indicate that the loss of the corner separation can be reduced with a dimples array, which is mainly related to the vertical climbing of the lateral flow that delays the starting point of the corner separation and weakens the mixing process. However, the loss in the wake of the dimpled cascades increases, which is caused by the thickened boundary layer induced by the high turbulent vortices. The dimpled cascade with $\lambda =0.625$ can achieve the most significant loss reduction (13.47%), while ensuring the pressurization capacity.

Active flow control should be adopted at more than one critical position in highly loaded aspirated compressors due to the severe flow separation and obvious three-dimensional characteristics of the flow field. A deep insight into the mechanism of the simplified compound boundary layer suction in a highly loaded compressor cascade was experimentally and numerically revealed in this paper. Locations of the two suction slots in the studied compound suction schemes were determined through previous experimental investigations on the single-slot suction schemes. Base on the one-side suction manner and the shared suction recycle system, the suction flow distribution over the suction surface slot (SS4) presented to be C-type along the spanwise both in single-slot cases and the compound suction schemes. On the other hand, the flow distribution over the endwall slot (EW1) was no longer that even along the axial direction after it cooperates with the SS4 slot, especially under the small total suction flow rate. The studied compound suction scheme owns obvious advantages in improving aerodynamic performance of the compressor cascade, when the total suction flow rate is big enough for both slots. About one-sixth loss reduction was achieved in the compound suction scheme with 1.5% suction flow rate. Therefore, the simplification of suction equipment via sharing one set of suction system and employing one-side suction manner is proved to be feasible and as effective in the studied multi-slot suction schemes.

The central curvature change of the S-shaped intake exacerbates the three-dimensional flow separation, resulting in total pressure and swirl distortions at the outlet. In this paper, an efficient active flow control technique, the sweeping jet actuator, was applied to control flow separation. The instantaneous characteristics of the flow field inside and outside the actuator were revealed by using validated numerical simulation methods. In addition, the effect of the sweeping jet on the aerodynamic performance of the S-shaped intake was investigated. Proper orthogonal decomposition (POD), an analysis method used to extract the main feature components of data, was applied to decompose the flow field structure at the S-shaped intake outlet in this study. The results highlight the external flow field characteristics of the actuator, with a jet sweeping range of up to ±40° and a sweeping frequency of 1 500 Hz, corresponding to a Strouhal number of 0.018. When the jet momentum coefficient is only 0.116%, the total pressure loss coefficient and pressure distortion index are reduced by 5.6% and 24.76%, respectively. This study demonstrates the critical role of momentum injection and discretization in inhibiting flow separation in the channel. The POD-based analysis indicates that a sweeping jet with high momentum can significantly enhance the energy in the flow passage and reduce the vorticity intensity of the first three modes. The stable mode structures exist near the outlet, exhibiting excitation frequency and frequency-doubling properties. The findings of this research provide essential input conditions for subsequent distortion studies.

In the experimental study of a compressor’s cascade under the near-stall condition, the test bench has the disadvantages of high risk and high maintenance cost. This paper explores a method of using the inlet guide vane to imitate near-stall conditions instead of the rotor. The suction groove is set in the sectorial cascade so as to explore the aerodynamic performance of the fluid and the change in the flow field structure. Three different schemes are proposed along the suction surface, and the results indicate that the EW2 scheme, which is located behind the separation starting point and near the vortex core of the separation vortex, has the best performance. The suction groove weakens the downwash caused by the boundary layer on the upper endwall, reducing the radial dimension of the corner and suppressing separation. Suction on the upper endwall also increases the pressure difference in the radial direction of the flow passage, resulting in a slight increase in the suction-side horseshoe vortex (HSV) at the hub. An overall loss reduction of 9.4% is achieved when the suction coefficient is 46%, and the corner separation is most effectively suppressed while ensuring that the HSV at the hub only slightly increases.

To clarify the flow control mechanism of the dimple surface and its influencing factors, this paper arranged cavity structures on the suction surface of a highly loaded compressor cascade. The Reynolds-averaged Navier–Stokes equations were utilized to calculate the impact of the geometric structure and inlet conditions of a dimple on the flow characteristics and flow control effect on the dimple surface. Additionally, the stress-blended eddy simulation was employed to compute the unsteady characteristics of the dimple vortex. By using the Liutex vortex determination criterion, flow regimes (diffuser-confuser, horseshoe vortex, and tornado-like vortex) and vortex axis morphologies (I-axis, C-axis, and V-axis) were identified. The flow regime diagram based on the Reynolds number and depth-to-diameter ratio was drawn, and boundary formulas for each flow pattern were provided. The vortex shedding frequency (1900–2300 Hz) and the main stream impingement frequency (5400–8154 Hz) for the cavity with a relative depth of 0.0625 were detected. By quantifying the vortex intensity coefficient and the increments of the inlet and outlet parameters of the cavity, the vortex and flow control capabilities were assessed. The results revealed that the peak vortex intensity occurred in the depth-to-diameter ratio range of 0.2–0.5, and the increase in dimple depth can improve the vortex intensity and delay the depth-diameter ratio corresponding to the peak value. The increment of turbulent kinetic energy and flow velocity at the outlet of the dimple to the flow field was proportional to the depth and inversely proportional to the depth-diameter ratio.