Performance Improvement Through Indexing of Turbine Airfoils: Part 1—Experimental Investigation

Abstract

This paper describes the results of a study to determine the performance improvements achievable by circumferentially indexing successive rows of turbine stator airfoils. An experimental/analytical investigation has been completed that indicates significant stage efficiency increases can be attained through application of this airfoil clocking concept. A series of tests was conducted at the National Aeronautics and Space Administration’s (NASA) Marshall Space Flight Center (MSFC) to experimentally investigate stator wake clocking effects on the performance of the Space Shuttle Main Engine Alternate Fuel Turbopump Turbine Test Article. Extensive time-accurate Computational Fluid Dynamics (CFD) simulations have been completed for the test configurations. The CFD results provide insight into the performance improvement mechanism. Part one of this paper describes details of the test facility, rig geometry, instrumentation, and aerodynamic operating parameters. Results of turbine testing at the aerodynamic design point are presented for six circumferential positions of the first stage stator, along with a description of the initial CFD analyses performed for the test article. It should be noted that first vane positions 1 and 6 produced identical first to second vane indexing. Results obtained from off-design testing of the “best” and “worst” stator clocking positions, and testing over a range of Reynolds numbers are also presented. Part two of this paper describes the numerical simulations performed in support of the experimental test program described in part one. Time-accurate Navier–Stokes flow analyses have been completed for the five different turbine stator positions tested. Details of the computational procedure and results are presented. Analysis results include predictions of instantaneous and time-average midspan airfoil and turbine performance, as well as gas conditions throughout the flow field. An initial understanding of the turbine performance improvement mechanism is described.

Vane Clocking Effects on Stator Loss for Different Compressor Loading Conditions

“…Much of the available clocking literature involves turbine applications, where as much as a a 2% stage efficiency benefit has been observed with optimal clocking [2][3][4]. These turbine experiments are supported by computational clocking studies [4,5], which show the potential for changes in stage efficiency from 0.7 to 2% with vane clocking.…”

An experimental investigation of the vane clocking effects on the centrifugal compressor time-averaged performance

“…One of the earliest vane clocking effect experiment was performed on a 2.5-stage turbine, 1 which showed that an efficiency difference of 0.3 points associated with vane clocking had been obtained, and that at local span the maximum efficiency variation could be 0.8 points, and even as much as 1.0 points at higher speed, but the variation calculated in subsequent numerical research was only 0.3 points. 2 Other clocking investigations on the turbines obtained similar results, the maximum efficiency variation influenced by vane clocking varied from 0.3 to 2.0 points.…”

Numerical and experimental investigation of unsteady flow interaction in a low-pressure multistage turbine

“…The nal goal of the present paper is to understand the underlying mechanisms of turbine stator clocking, which denotes the interaction of an upstream wake of a stator with the next stator, which has the same blade count. Although several studies on turbine clocking have been presented [14][15][16], the phenomenon is not fully understood yet.…”