Abstract
Five-Hole Probes (FHP), being a dependable and accurate aerodynamic tool, are an excellent choice for measuring three-dimensional flow fields in turbomachinery. To improve spatial resolution, a subminiature FHP with a diameter of 1.68 mm is employed. High length to diameter ratio of the tubing and manual pitch and yaw calibration cause increased uncertainty. A new FHP calibrator is designed and built to reduce the uncertainty by precise, computer controlled movements and reduced calibration time. The calibrated FHP is then placed downstream of the nozzle guide vane (NGV) assembly of a low-speed, large-scale, axial flow turbine. The cold flow HP turbine stage contains 29 vanes and 36 blades. A fast and computer controllable traversing system is implemented using an adaptive grid method for the refinement of measurements in regions such as vane wake, secondary flows, and boundary layers. The current approach increases the possible number of measurement points in a two-hour period by 160%. Flow structures behind the NGV measurement plane are identified with high spatial resolution and reduced uncertainty. The automated pitch and yaw calibration and the adaptive grid approach introduced in this study are shown to be a highly effective way of measuring complex flow fields in the research turbine.
Highlights
Five-Hole Probes are used to determine the three components of the mean velocity vector, local total pressure, and local static pressure [1]
They work by selectively comparing pressure data from five ports on the probe
The present paper presents significant improvements in Five-Hole Probes (FHP) based aerodynamic measurements in four significant areas
Summary
Five-Hole Probes are used to determine the three components of the mean velocity vector, local total pressure, and local static pressure [1]. According to Treaster and Yocum [2], by comparing the pressure differences between these ports, flow velocity magnitude, pitch angle, yaw angle, total pressure, and static pressure can be simultaneously determined. This method is found to work in a range of ±30∘ of pitch and yaw angle. Reichert and Wendt suggest another method of data reduction for the FHP [6] This method replaces the pitch and yaw angles with unit vectors and develops a Taylor series based approach to find flow parameters. Pisasale and Ahmed [13] presented a theoretical calibration approach for a FHP for highly three-dimensional flows. The new system increases the number of data points that can be collected in a two-hour period from 366 points to 868 points, an increase of 160%
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