Synthetic Separation Control Using Vortex Generator and Slot Jet in a High Load Compressor Cascade

Abstract

The compressor cascade performance is significantly restricted by the secondary flow mainly presented as the trailing edge separation and corner stall. This paper develops a synthetic flow control approach in a high turning cascade using the vortex generator and slot jet approach. Numerical simulations were conducted to assess the flow control benefits and illustrate the flow control mechanisms. Four configurations, the baseline, the two individual approaches and the synthetic approach, were simulated to compare the separation control effects. The simulations show that all the three configurations achieve considerable improvements of the cascade performance and the cascade sensitivity to incidence angle is greatly decreased. The synthetic approach improves the most among them which is almost the superposition of the two individual ones. In the synthetic approach, the trailing vortex induced by the vortex generator suppresses the end wall cross flow and deflects the passage vortex, and then prevents the production of corner stall; at the same time, the slot jet speeds up the trailing edge separation caused by the cascade high camber. Owing to the combination of the two aspects, the synthetic approach restricts the developments of secondary flow and vortices in the cascade, and improves the outflow uniformity. The synthetic approach nicely utilizes the advantages of the two individual approach while avoids the shortages by the complementation, so it can achieve more powerful flow control effects. At the end, vortices models are established to illustrate the secondary flow structure and the flow control mechanisms.

Effect of optimal slot location on the performance of cascades of blades

“…Additionally, the occurrence of softer peaks in θ and ω curves for 28.93°in Figures 8 and 9 confirms a statement that the separation zone is too large to be removed by slot treatment-as stated before. 20,32 When comparing the performance criteria of the slotted profile of IG-25 with the baseline profile at two higher levels of the angle of attack, it shows not only a better performance under the same operating angle but also in comparison with the baseline profile in the design condition.…”

“…An analysis of the flow field will identify any secondary flow patterns; with the aid of numerical limiting streamlines and flow patterns (topology) near surfaces, complex rotating vortices and the mechanisms of their development along the passage will be revealed. Similar studies have used this approach for either topological investigation of the flow pattern near end walls 1,3,20,21 or as a strategy to enhance the flow control methods. 7,30,40 Figure 10 presents limiting streamlines on the vertical section of the blade near the end wall for both the slotted and baseline profiles at an angle of attack of 28.93°.…”

“…19 The mixture of boundary layers often leads to the formation of corner vortices (CVs), cross flow patterns, spanwise flow deviation, and passage vortices. 15,20,21 All these are considered as the main sources of inefficiency in a compressor stage in particular and the whole GT engine in general. 22,23 This is a motivation for researchers to put their focus on performance optimization of turbo machinery far more than other fields.…”

“…Kundu 9 reported the 2°delay in stall margin, while Ni et al 8 indicated that a maximum 58% increase in lift and 14% in lift-to-drag ratio obtained with their novel slot design on a WT blade. Hu et al 15,20,34 performed a serial research on the impact of the span slot, VG, and the combined effect of each on a compressor blade's capacity. The positive capability of the slot in affecting the trailing edge (T.E.)…”

Influences of slotted blade on performance and flow structure of a transonic axial compressor

“…The jet flow can decrease thickness of the boundary layer on suction surface and delay the onset of flow separation. 7 The slotted blade was firstly proposed by Rockenbach, 8 whose experimental results showed that mid-span flow structure of the rotor blade was improved but the method made a poor effect at endwall region. An experimental investigation of a highly-loaded compressor cascade with a full-span slot was studied by Hu et al 9 The results showed that total pressure loss of the cascade was reduced by 21.9%, average flow turning angle was increased by 2.1 , and range of the incidence angle was widened by 3 at least.…”