Secondary Flow, Turbulent Diffusion, and Mixing in Axial-Flow Compressors

Abstract

The relative importance of convection by secondary flows and diffusion by turbulence as mechanisms responsible for mixing in multistage, axial-flow compressors has been investigated by using the ethylene tracer-gas technique and hot-wire anemometry. The tests were conducted at two loading levels in a large, low-speed, four-stage compressor. The experimental results show that considerable cross-passage and spanwise fluid motion can occur and that both secondary flow and turbulent diffusion can play important roles in the mixing process, depending upon location in the compressor and loading level. In the so-called freestream region, turbulent diffusion appeared to be the dominant mixing mechanism. However, near the endwalls and along airfoil surfaces at both loading levels, the convective effects from secondary flow were of the same order of magnitude as, and in some cases greater than, the diffusive effects from turbulence. Calculations of the secondary flowfield and mixing coefficients support the experimental findings.

A new finite difference method to solve the velocity gradient equation in streamline curvature method

“…Most through flow codes use the streamline curvature method and derive from those of Hamrick et al, turbulent diffusion play important roles in the mixing process, 12,13 Casey and Robinson 14 proposed a new model applied to the streamline curvature method for spanwise mixing of angular momentum, total enthalpy, and entropy across the meridional streamtubes.…”

Predictions of the Flow in Repeating Stages of Axial Compressors Using Navier-Stokes Solvers

“…In recent years there has been much discussion of whether spanwise mixing takes place due to the secondary flows or by dissipative turbulent diffusion (see Gallimore and Cumpsty, 1986, for example). Wisler et al (1987) subsequently concluded that both effects are present. Later, Leylek and Wisler (1991) suggested that geometrical configuration and aerodynamic loading would control the relative strengths of the two, but that secondary flow induced mixing was stronger near the annulus walls.…”

Three-Dimensional Flow and Mixing in an Axial Flow Compressor With Different Rotor Tip Clearances

“…Kotidis and Epstein (1990) studied mixing across a transonic rotor and proposed a quasi-three-dimensional vortex street model as another mechanism of spanwise mixing. In the course of the research, Wisler et al (1987) found much higher mixing levels in endwall regions; more recently Li and Cumpsty (1990) highlighted the dominant effect of unsteadiness, generated by rotor tip leakage flows, on mixing across the downstream stator blade row. Accordingly, the investigation on the effect of difference in rotor tip clearance in terms of mixing has surfaced as another point of interest in the research on endwall flows.…”

“…There has been extensive research carried out on mixing in multistage axial flow compressors, in regard to the relative importance between secondary flows and turbulent diffusion as the mechanism of mixing process (Adkins and Smith, 1982;Gallimore and Cumpsty, 1986;Wisler, Bauer and Okiishi, 1987 ;Leylek and Wisler, 1990;Li and Cumpsty, 1990). Kotidis and Epstein (1990) studied mixing across a transonic rotor and proposed a quasi-three-dimensional vortex street model as another mechanism of spanwise mixing.…”