Spanwise Mixing in Axial-Flow Turbomachines

Abstract

Flow measurements taken in multistage axial-flow turbomachines suggest that substantial spanwise mixing of flow properties often occurs. In addition, measured blade row turnings often show considerable deviation from two-dimensional cascade theory, particularly in the end-wall regions. An approximate method is presented with which both of these effects can be included in design through-flow calculations. The method is based on inviscid, small-perturbation secondary flow theory. Frictional effects are not directly included but secondary flows caused by annulus wall and blade boundary layers are included in an approximate way. The secondary flow model includes effects of 1) main-stream nonfree-vortex flow, 2) end-wall boundary layers, 3) blade end clearances, 4) blade end shrouding, and 5) blade boundary layer and wake centrifugation. The spanwise mixing phenomenon is modeled as a diffusion process, where the mixing coefficient is related to the calculated spanwise secondary velocities. Empirical adjustments are employed to account for the dissipation of the secondary velocities and interactions with downstream blade rows. The induced blade row overturnings are related to the calculated cross-passage secondary velocities. The nature of the assumptions employed restricts the method to design-point-type applications for which losses are relatively small and significant regions of separated flow are not present.

Phase-averaged flow statistics in compressors using a rotated hot-wire technique

“…Note that data are shown for three blade passing periods and have been normalised using the rotor speed at mid-height, U m , and the stator pitch, s where terms I and II show the phase-integrated effect of the deterministic and Reynolds stresses against the mean flow, respectively. The competing effects of deterministic and stochastic unsteadiness upon compressor performance have been a hotly debated topic ever since the works of Adkins and Smith (1982) and Gallimore and Cumpsty (1986). Furthermore, the phase-locked statistics reported in this paper will enable comparisons against other scale-resolving measurement techniques, such as three-component particle image velocimetry (Bhattacharya et al 2016), and high fidelity numerical simulations (Brandvik and Pullan 2009) to be made.…”

Study of modeling unsteady blade row interaction in a transonic compressor stage part 1: code development and deterministic correlation analysis

“…The model was developed within the framework of "mixing-plane"-type prediction scheme designed to model multistage compressor flows accurately with the minimum of computational complexity. Ji [9] proposed a semi-empirical model based on the spanwise mixing model proposed by Adkins & Smith [10]. Gao et al [11] modified Ji's model for centrifugal compressors based on experiments.…”

Investigating Circumferential Non-Uniformities in Throughflow Calculations Using an Harmonic Reconstruction

“…In classical throughfows, these averaged 3D flow features are partly taken into account by empirical models [13]- [16]. The quality of the prediction relies then on experimental data.…”