Three-Dimensional Separations in Axial Compressors

Abstract

Flow separations in the corner regions of blade passages are common. The separations are three dimensional and have quite different properties from the two-dimensional separations that are considered in elementary courses of fluid mechanics. In particular the consequences for the flow may be less severe than the two-dimensional separation. This paper describes the nature of three-dimensional separation and addresses the way in which topological rules, based on a linear treatment of the Navier-Stokes equations, can predict properties of the limiting streamlines, including the singularities which form. The paper shows measurements of the flow field in a linear cascade of compressor blades and compares these with the results of 3D CFD. For corners without tip clearance, the presence of three-dimensional separation appears to be universal and the challenge for the designer is to limit the loss and blockage produced. The CFD appears capable of predicting this.

Numerical Study of the Effect of Secondary Vortex on Three-Dimensional Corner Separation in a Compressor Cascade

“…However, this issue is difficult to manage and control. This is perhaps primarily because the nature and characteristics of 3D separations in compressors are not clearly understood, nor are the mechanisms and factors that influence their growth and ultimate size [4].…”

“…Therefore, the extent of low-energetic fluid accumulation in the non-slip case is greater than that in the slip case, which indicates the secondary flow is important in this phenomenon. As suggested by Gbadebo et al [4], the thickness of 3D separated layer can be simply denoted using the concept of relative displacement thickness δ Ã eff , which is defined as follows:…”

“…The low-momentum fluid within the hub boundary layer was transported toward the suction side of the blade by this vortex. Gbadebo et al [4] once considered the leading-edge horseshoe vortex plays a major role in mechanism of 3D separation. These studies indicate that 3D corner separation is closely related to the secondary flow in compressor cascades.…”

Evaluation of RANS turbulence models in simulating the corner separation of a high-speed compressor cascade

“…Email: wuyun1223@126.com Spakovszky, & Greitzer, 2008;Schulz, Gallus, & Lakshminarayana, 1990). Because of its dramatic impact on compressor performance, corner separation has been studied both experimentally and numerically with the progress of axial compressor design techniques using compressor cascade models (Chen, Qiao, Liesner, & Meyer, 2014;Evans, Hodson, Hynes, & Wakelam, 2010;Gbadebo, Cumpsty, & Hynes, 2005Zachos, Grech, Charnley, Pachidis, & Singh, 2011).…”

Role of Hub-Corner-Separation on Rotating Stall in an Axial Compressor

“…However, little attention has been paid to role of hub-corner-separation on the rotating stall although it is a common flow feature in an axial compressor operating near the stall point, exerting a large effect on internal flows and loss characteristics. Although some researchers [25][26][27][28] have investigated the structure of corner separation and its impact on internal flows in an axial compressor, only Day 5) noted that corner separations occurred throughout his stall tests, and that the size of these separations was changed periodically by the modal wave. However, there is still no definitive explanation of the cause of the rotating stall to date.…”