Investigation of Tip Clearance Phenomena in an Axial Compressor Cascade Using Euler and Navier–Stokes Procedures

Abstract

Three-dimensional Euler and full Navier–Stokes computational procedures have been utilized to simulate the flow field in an axial compressor cascade with tip clearance. An embedded H-grid topology was utilized to resolve the flow physics in the tip gap region. The numerical procedure employed is a finite difference Runge-Kutta scheme. Available measurements of blade static pressure distributions along the blade span, dynamic pressure and flow angle in the cascade outlet region, and spanwise distributions of blade normal force coefficient and circumferentially averaged flow angle are used for comparison. Several parameters that were varied in the experimental investigations were also varied in the computational studies. Specifically, measurements were taken and computations were performed on the configuration with and without: tip clearance, the presence of an endwall, inlet endwall total pressure profiles and simulated relative casing rotation. Additionally, both Euler and Navier–Stokes computations were performed to investigate the relative performance of these approaches in reconciling the physical phenomena considered. Results indicate that the Navier–Stokes procedure, which utilizes a low Reynolds number k–ε model, captures a variety of important physical phenomena associated with tip clearance flows with good accuracy. These include tip vortex strength and trajectory, blade loading near the tip, the interaction of the tip clearance flow with passage secondary flow, and the effects of relative endwall motion. The Euler computation provides good but somewhat diminished accuracy in resolution of some of these clearance phenomena. It is concluded that the level of modeling embodied in the present approach is sufficient to extract much of the tip region flow field information useful to designers of turbomachinery.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

“…It is believed that in the fore part of the blade the shock-wave surface separates the leakage flow from the secondary flows between the shock-wave and the pressure-side of the blade. When, as the fl ow progresses downstream, the leakage flow crosses the shock-wave, it interacts both with the shock wave and with the pressure-side secondary flows generating a leakage-interaction-region of low speed, high entropy and high turbulence, in a way analogous to the subsonic case described by Lakshminarayana et al (1995). Further re search is needed to investigate the relative importance of shock-wave/vortex interaction and vortex/pressure-side-fl ow interaction in the generation of tip-clearance losses.…”

“…A few modern studies are interested in the numerical com putation of the flow through the gap, as part of the solu tion (Rai, 1989a(Rai, , 1989bLiu and Bozzola, 1993;Kunz et al, 1993;Basson and Lakshminarayana, 1995;Copenhaver et al, 1996Copenhaver et al, , 1997Hah and Loellbach, 1997;Steinthorsson, 1995, 1996;Ameri et al, 1997). With the exception of Ameri et al (1995Ameri et al ( , 1996Ameri et al ( , 1997, these studies use very few points within the tip-clearance-gap (Tab.…”

“…In the present transonic flow, from the leading-edge to plane o, the shock-wave is seen to separate the leakage flow from the passage secondary flow occuring in the region between the shock-wave and the pressure-side (Fig 8) When the leakage flow crosses the shock-wave it in teracts with the passage secondary flow creating the leakage interaction-region It is plausible to assume that there is a direct analogy between the subsonic and transomc case, and that the shock-wave acts as a barrier between the pressure side secondary flows and the leakage flow. When this barrier is crossed the leakage-interaction-region is created in much the same way as in the subsonic flow case (Lakshminarayana et al, 1995), with the additional effect of vortex growth and axial velocity deficit due to the interaction with the shock wave.…”

Advances in large eddy simulation methodology for complex flows

“…This mesh topology is often extended to the ''embedded H-type mesh'' to facilitate the treatment of the tip-clearance region (e.g., Kunz et al, 1993). However, the embedded H-mesh has significant drawbacks.…”

Large-eddy simulation of a rotor tip-clearance flow

“…A commonly used mesh topology is the "embedded H-type mesh" (e.g., Ref. [14]). However, the embedded H-mesh has significant drawbacks.…”