Encounters with Vortices in a Turbine Nozzle Passage

J P Gostelow,A Rona,W E Carscallen,A Mahallati

doi:10.1155/2012/928623

Abstract

Experiments were conducted on the flow through a transonic turbine cascade. Secondary flows and a wide range of vortex types were encountered, including horseshoe vortices, shock-induced passage vortices, and streamwise vortices on the suction surface. In the separation region on the suction surface, a large rollup of passage vorticity occurred. The blunt leading edge gave rise to strong horseshoe vortices and secondary flows. The suction surface had a strong convex curvature over the forward portion and was quite flat further downstream. Surface flow visualization was performed and this convex surface displayed coherent streamwise vorticity. At subsonic speeds, strong von Kármán vortex shedding resulted in a substantial base pressure deficit. For these conditions, time-resolved measurements were made of the Eckert-Weise energy separation in the blade wake. At transonic speeds, exotic shedding modes were observed. These phenomena all occurred in experiments on the flow around one particular turbine nozzle vane in a linear cascade.

Highlights

Leonardo da Vinci (1452–1519) was a notable early observer of vortices produced by a solid object placed in a stream of flow (Figure 1)
A wide range of vortex formation and shedding processes was identified in a transonic turbine nozzle cascade
Observations of the streamwise streaks have generally been by surface flow visualization

Summary

Introduction

Leonardo da Vinci (1452–1519) was a notable early observer of vortices produced by a solid object placed in a stream of flow (Figure 1). Vortex shedding, energy separation, base pressures, and exotic shedding modes are observed This is all in experiments on the flow around one particular turbine nozzle vane in a linear cascade. Examples will be given which should result in a questioning of the assumption that the organized streamwise vorticity is confined to the pressure surface of a turbine blade It appears to be unusual, this behavior had been predicted and observed previously with attendant theories for wavelength. In this ostensibly adiabatic arrangement, the central regions of the vane wakes exhibited a significant decrease in total temperature and their edges showed an unexpected increase To resolve these anomalies and obtain detailed information over the Mach number range, the midspan section of the nozzle was tested in a large scale, low aspect ratio, and transonic planar cascade [4]. Findings from the vortex-induced vibration work of Williamson and Roshko [8] have clarified the shedding modes

Vortices in the Blade Passage

Figure 6

Vortex Shedding

Findings

Conclusions