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A systematic and comprehensive investigation was performed to provide detailed data on the three dimensional viscous flow phenomena downstream of a modem turbine rotor and to understand the flow physics such as origin, nature, development of wakes, secondary flow, and leakage flow. The experiment was carried out in the Axial Flow Turbine Research Facility (AFTRF) at Penn State, with velocity measurements taken with a 3-D LDV System. Two radial traverses at 1% and 10% of chord downstream of the rotor have been performed to identify the three-dimensional flow features at the exit of the rotor blade row. Sufficient spatial resolution was maintained to resolve blade wake, secondary flow, and tip leakage flow. The wake deficit is found to be substantial, especially at 1% of chord downstream of the rotor. At this location, negative axial velocity occurs near the tip, suggesting flow separation in the tip clearance region. Turbulence intensities peak in the wake region, and cross- correlations are mainly associated with the velocity gradient of the wake deficit. The radial velocities, both in the wake and in the endwall region, are found to be substantial. Two counter-rotating secondary flows are identified in the blade passage, with one occupying the half span close to the casino and the other occupying the half span close to the hub. The tip leakage flow is well restricted to 10% immersion from the blade tip. There are strong vorticity distributions associated with these secondary flows and tip leakage flow. The passage averaged data are in good agreement with design values. Lakshminarayana, B. and Ristic, D. and Chu, S. Glenn Research Center AXIAL FLOW TURBINES; BLADE TIPS; BOUNDARY LAYER SEPARATION; FLUID DYNAMICS; SPATIAL RESOLUTION; THREE DIMENSIONAL FLOW; VISCOUS FLOW; VORTICITY; WAKES; COUNTER ROTATION; FLOW DISTRIBUTION; RADIAL VELOCITY; SECONDARY FLOW; SEPARATED FLOW; TURBINES; VELOCITY DISTRIBUTION; VELOCITY MEASUREMENT...
Presented at the International Gas Turbine and Aeroengine Congress & Exhibition Birmingham, UK - June 10-13, 1996.
Three dimensional flow field measurements are presented for a large scale transonic turbine blade cascade. Flow field total pressures and pitch and yaw flow angles were measured at an inlet Reynolds number of 1.0 x 10(exp 6) and at an isentropic exit Mach number of 1.3 in a low turbulence environment. Flow field data was obtained on five pitchwise/spanwise measurement planes, two upstream and three downstream of the cascade, each covering three blade pitches. Three hole boundary layer probes and five hole pitch/yaw probes were used to obtain data at over 1200 locations in each of the measurement planes. Blade and endwall static pressures were also measured at an inlet Reynolds number of 0.5 x 10(exp 6) and at an isentropic exit Mach number of 1.0. Tests were conducted in a linear cascade at the NASA Lewis Transonic Turbine Blade Cascade Facility. The test article was a turbine rotor with 136 deg of turning and an axial chord of 12.7 cm. The flow field in the cascade is highly three dimensional as a result of thick boundary layers at the test section inlet and because of the high degree of flow turning. The large scale allowed for very detailed measurements of both flow field and surface phenomena. The intent of the work is to provide benchmark quality data for CFD code and model verification.
This paper presents an exhaustive experimental documentation of the three-dimensional nature of the flow in a one-and-one-half stage axial turbine. The intent was to examine the flow within, and downstream of, both the stator and rotor airfoil rows so as to delineate the dominant physical mechanisms. Part 1 of this paper presented the aerodynamic results. Part 2 presents documentation of the mixing, or attenuation, of a simulated spanwise inlet temperature profile as it passed through the turbine, including: (1) the simulated combustor exit-turbine inlet temperature profile, (2) surface measurements on the airfoils and endwalls of the three airfoil rows, and (3) radial-circumferential distributions downstream of each airfoil. Although all three rows contributed to profile attenuation, the impact of the rotor was strongest.
While strongly three dimensional and highly unsteady nature of the flow in axial turbines has, until recently, defied in-depth analysis, the benefits that can be realized from an improved capability to predict the aerodynamics and heat transfer in turbines are numerous. These benefits include improved performance through higher efficiency, higher thrust-to-weight ratio through higher turbine inlet temperature, and improved durability through more precise predictions of local heat load. This program was particularly interested in the aerodynamic mechanisms affecting attenuation of a radial temperature profile in the flow as it passed through the turbine. The radial temperature profile in the flow exiting a combustor and entering a turbine can range from compressor exit temperature (approx = 1100 F) near the hub and tip end walls to a maximum (as high as 3200 F) in the midspan region. The heat load at any location on the turbine airfoils or end walls depends strongly on the local gas temperature at that location; hence the mixing, or attenuation, of the inlet temperature profile is of critical importance. This program has advanced the state-of-the-art by providing: 1) an exhaustive aerodynamic data base for the three dimensional flow in a large scale axial turbine; 2) an exhaustive data base documenting the mixing of a simulated combustor exit temperature profile as it passed through the turbine; and 3) an assessment of sota three dimensional time accurate, Navier-Stokes prediction of the flow in the turbine stage. Keywords: Temperature redistribution. (EDC).