Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 1—Framework of Technical Approach and Wake–Stator Blade Interactions

Abstract

In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stators with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flow field showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 1, the focus will be on the framework of technical approach, and the interaction of stator with the moving upstream rotor wakes.

Effect of Upstream Unsteady Flow Conditions on Rotor Tip Leakage Flow

“…An alternative opportunity to assess the comparison method was to run a twodimensional case with boundary layers on the blade surfaces and quantify the effect of upstream wake velocity defect on boundary layer loss. Such a study by Valkov [24] showed that the loss increases linearly with upstream wake velocity defect. Computations were carried-out for three different wake sizes and the results are in accord with Valkov's findings (Figure 2.5), which were based on using a high order numerical scheme, namely, the spectral element method.…”

Numerical Study on Unsteadiness of Tip Clearance Flow and Performance Prediction of Axial Compressor

“…It seems that the mixing-plane assumption at the interfaces between the rotating and stationary domains causes this discrepancy. The beneficial effects of blade row interaction on rotor performance were studied by Valkov and Tan [12], Sirakov and Tan [13], and Graf et al [14]. Valkov and Tan [12] showed that the upstream wake recovery increased the pressure rise in the downstream passage by 1 to 3%.…”

“…The beneficial effects of blade row interaction on rotor performance were studied by Valkov and Tan [12], Sirakov and Tan [13], and Graf et al [14]. Valkov and Tan [12] showed that the upstream wake recovery increased the pressure rise in the downstream passage by 1 to 3%. Sirakov and Tan [13] explained that the upstream wake suppressed double leakage of the tip clearance flow, thereby enhancing the pressure rise by about 2%.…”

Effects of Periodic Wake Passing Upon Aerodynamic Loss of a Turbine Cascade: Part I — Measurements of Wake-Affected Cascade Loss by Use of a Pneumatic Probe

“…Relevant discussions were made in detail by Adamczyk (1996). Deregel and Tan (1996) and Valkov and Tan (1998) for compressor stages, referring to 'wake recovery model of Smith (1966). Even though such a wake recovery existed in the present cascade, it seemed quite difficult to distinguish it from the viscous effect.…”