Loss Reduction in Compressor Cascades by Means of Passive Flow Control

Abstract

Secondary flow effects like the corner stall between the wall and the vane in a compressor stage are responsible for a large part of total pressure losses. An extensive experimental study of flow control in a highly loaded compressor cascade was performed in order to decrease the separation and reduce the losses by means of vortex generators. The vortex generators were attached at the surface of the cascade side walls. These flow control devices produce strong vortices, which enhance the mixing between the main flow and the decelerated boundary layer at the side wall. Thus, the corner flow separation and the total pressure losses could be reduced. The experiments were carried out with a compressor cascade at a high-speed test facility at the DLR in Berlin at minimum loss (design point) and off-design of the cascade at Reynolds numbers up to Re = 0.6 × 106 (based on 40 mm chord) and Mach numbers up to M = 0.7. The cascade consisted of five vanes. The blade profiles are comparable to the hub section of the stator vanes used in the transonic compressor test rig running at Technische Universita¨t Darmstadt. In the range between −2° and +4° angle of incidence the total pressure losses of the cascade could be reduced up to 4.6% by means of vortex generators, whereas the static pressure rise was not influenced. Based on the results of the cascade measurements, the vortex generators were applied in front of the stator row of the single stage axial compressor at Technische Universita¨t Darmstadt. A numerical simulation of the compressor flow provided an indication for the adjustment of the vortex generators at the hub and casing. In the experiments the pressure rise and the efficiency of the axial compressor was measured and it could be shown that vortex generators partially improve the efficiency.

Active Flow Control on a Highly Loaded Compressor Cascade with Non-steady Boundary Conditions

“…Using side wall actuation mainly influences the secondary flow structures. It has been demonstrated that vortex generators on the side wall of a two-dimensional high-speed cascade can result in a reduced total pressure loss [8]. Blade actuators avoid flow separation on the blade itself.…”

Experimental investigation on a high subsonic compressor cascade flow

“…12,13 Active flow control methods, such as boundary layer suction, [14][15][16] flow blowing, 17,18 plasma flow control 19,21 etc, have been applied to the control of compressor cascade corner separations over years. Meanwhile, the application of passive flow control methods, such as vortex generator, [22][23][24] endwall contouring 25 etc, as well as combination of passive and active control methods, 26 for corner separation control have been investigated with great efforts. To control the corner separation effectively, the design of both active and passive methods should be based on the in-depth understanding of flow structures in the compressor cascade flow passage and various efforts have been spared.…”

Control of Corner Separation with Plasma Actuation in a High-Speed Compressor Cascade

“…This high-speed compressor cascade model is designed by the research group DLR (German Aerospace Center) and has been used broadly to study the flow control of high-speed compressor cascade corner separations (see, for example, [4,5,[8][9][10]). Its main geometrical and aerodynamic parameters are shown in Table 1.…”

“…Passive flow control methodologies such as boundary layer fences [4,5], non-axisymmetric endwall contouring [6,7], and vortex generators [8][9][10] etc. can effectively reduce the detrimental effects of corner separations on the design conditions.…”