Session: 34-05 Flow Control

Paper Number: 82258

82258 - Evolution of Turbulence and Its Modification by Axial Casing Grooves in a Multi-Stage Axial Compressor 

Data on the evolution of Reynolds stress in a multi-stage axial compressor is essential for understanding the flow dynamics and for benchmarking numerical predictions. This paper examines the distribution of turbulent kinetic energy (TKE), Reynolds stress (6 components), mean strain rate tensor, and production rates of the various stress components in a series of axial planes along the machine. It also discusses the modifications to these terms caused by installing semicircular axial casing grooves (ACGs), which significantly reduces the stall flowrate. The stereo-PIV measurements are performed in the one and a half stage compressor installed in the JHU refractive index matched facility. The present fields of view cover entire passages, from the hub to the tip, in axial planes located upstream of the IGV, in the IGV-rotor gap, within the rotor, in the rotor-stator gap, within the stator, and downstream of the stator. Within the rotor, these planes intersect with the blades at z/c_a=0.28 and 0.89, and within the stator, at z/c_a=0.10 and 0.71. Data are obtained at flow rates corresponding to the pre-stall conditions and the best efficiency point (BEP) of the untreated endwall. Upstream of the rotor, at the pre-stall flowrate, the TKE is high in the IGV wakes and in the tip region, the latter owing to intermittent upstream-propagating backflows. The axial component of the TKE is the dominant contributor, peaking near the pressure side of the blade, and axial contraction is the dominant contributor to its production. The ACGs increase the TKE in the tip region due to the interactions between the outflow from the groove and the incoming passage flow. At z/c_a=0.28, the turbulence is particularly high in the tip region, where the axial velocity is low, and the flow is dominated by the tip and backflow vortices. The circumferential and the axial normal Reynolds stress components are the dominant contributors, and shear production at the interface between the tip region with high circumferential velocity and low axial velocity, and the rest of the passage is the largest source of turbulence. While the area with high circumferential fluctuations shrinks as the trailing edge (TE) is approached, the axial component and its shear production rate remain high at the interface between low and high axial momentum regions. This trend continues in the post-rotor plane. Here, the instantaneous axial velocity is occasionally negative, more prominently in the tip region, and the corresponding RMS values are as high as 50% of the mean velocity. With the ACG, the area with tip blockage is much smaller and the TKE is substantially lower. As the flow passes through the stator passage, for the smooth endwall, there is a significant reduction in turbulence level over most of the passage. At z/c_a=0.10, there is significant negative turbulence production owing to axial extension of the flow in the top half of the passage. However, the TKE remains high over substantial fractions of the stator due to advection of previously generated turbulence. In contrast, at z/c_a=0.71, the turbulence increases along the lower suction side of the stator boundary layer, with axial contraction being the primary production term. These trends persist downstream of the stator. Installing the ACG reduces the TKE everywhere downstream of the stator, and its peak becomes distributed along a much narrower stator wake compared to that of the smooth endwall. At high flowrate, the TKE is much lower in all the investigated planes. Upstream of the rotor, the TKE is elevated only in the IGV wake, with almost equal contributions from all its components, i.e., the turbulence is more isotropic. Whereas for ACGs, groove-passage interactions increase the TKE in the tip region. Downstream of the rotor, as well as within and downstream of the stator, the flow structure and distribution of turbulence level for the smooth endwall and with the ACG installed appear to be similar.

Presenting Author: Ayush Saraswat Johns Hopkins University

Presenting Author Biography: TBA

Authors:

Subhra Shankha Koley Johns Hopkins University
Ayush Saraswat Johns Hopkins University
Joseph Katz The Johns Hopkins University