Study on Optimization Design and Flow Control Mechanism of Little Blades in a Compressor Cascade

Abstract

In view of the characteristics of flow separation in the compressor cascade corner region, a new flow control method for installing little blades in the front of the cascade passage was proposed, which took into account the flow control advantages of end wall fences and vortex generators. Firstly, the little blades could hinder the cross flow on the end wall and the development of the horseshoe vortex pressure surface branch. Secondly, the little blades could generate induced vortices to take away the low-energy fluid near the end wall and the corner region. Based on numerical simulations, the effects of different pitchwise positions, stagger angles and heights of the little blades on the aerodynamic performance of the cascade were studied, and the optimal little blades were obtained by NSGA-II using EBF neural network as the agent model. The results show that the little blades have the optimal pitchwise position, stagger angle and height range for improving the aerodynamic performance of the cascade. When the optimized little blades are introduced in the baseline cascade, the stable working range of the cascade is expanded, and the stall type of the cascade changes from the hub-corner stall to the overload of flow separation near the mid-span. At the near stall attack angle of the baseline, the total pressure loss coefficient is reduced by about 10.38% and the static pressure coefficient is increased by about 4.31%. Meanwhile, the loss of the lower span is decreased and the diffuser capacity of the whole span is improved. The passage secondary loss and wake loss are reduced because of the delay of corner separation. Moreover, the strength of the end wall vortex is weakened and the end wall vortex no longer develops as part of the passage vortex. The induced vortex, horseshoe vortex pressure surface branch and initial passage vortex develop into new passage vortex.

Optimization study on the influence of little blades’ spatial position on a compressor cascade performance

“…Some geometric parameters of LBs have been fully discussed in previous studies. 17,21 Therefore, the influence of LBs position on the cascade performance is further discussed in this article. The position parameters of the LBs are set according to the characteristics of the blade profile and blade passage.…”

“…In Figure 13, the distance between the two vanes ( S ) and the length ( L ) are defined according to some previous research studies focused on the effects of geometric parameters of the LBs on cascade performance. 17 Moreover, the stagger angle ( χ ) of the LBs at the stall condition (8° incidence) has been optimized by Guo, 21 and the optimal value is 1.29 γ . In the previous research studies, 17 the leading edge of the little blade with a smaller size shows an obvious superiority in reducing the total pressure loss at some larger incidence conditions; therefore, h L is lower than h T .…”

“…The micro-vortex generator has been applied into the blade passage 21 because the MVG located on the end-wall in front of the leading edge is limited by the axial distance between the stator and the upper rotor. The rotor/stator interaction has become an important factor, so it must be considered in the design process of the flow control device.…”

Applications of little blades in a high-load compressor cascade with leaned blade

“…It has been proved that the spatial positions and geometric parameters of little blades can affect the cascade performance. The stagger angle (v) and pitchwise position (d) have been optimized by Guo et al 32 and the values of optimal v and d are 1.29c and 0.6t respectively. The distance between the two little blades (S), the height (h T ) and the length (L) are defined according to previous researches focused on the effects of geometric parameters of the little blade on cascade performance.…”

“…Therefore, the inter-stage matching has become a factor must be considered in the design of the flow control device near the endwall. 32 When the vane-type vortex generator is placed on the end-wall in the cascade passage, the secondary flow near the end wall is weakened and the pitchwise migration of the boundary layer is suppressed, thus the accumulation of the cross-flow near the end-wall in the corner region is controlled. 33 Above all, the aerodynamic performance of an axial compressor cascade is discussed, and the effects of compound lean on the compressor cascade is analyzed based on the aerodynamic performance.…”