Steady and unsteady calibration of multi-hole probes

Abstract

This thesis presents the development of a data crographics. reduction algorithm for multi-hole pressure probes. The algorithm has been developed for the reduction of calibration data from miniature non-nulling multi-hole probes in compressible, subsonic flow gelds. The algorithm is able to reduce data from any 5-or 7-hole probe in a subsonic flow field and generate very accurate predictions of the velocity magnitude and direction, total and static pressure, Mach and Reynolds member and fluid properties like the density and viscosity. The algorithm utilizes a local least-squares modeling technique and has been tested on 4 novel miniature 7-hole probes that have been calibrated at NASA Langley Flow Modeling and Control Branch for the entire subsonic regime. Each of the probes had a conical tip with diameter of 0.065''. Excellent prediction capabilities are demonstrated with maximum errors in angle prediction less than 0.6 degrees and maximum errors in velocity prediction less than 1%, both with 99 percent confidence. The development of Micro Electro Mechanical Systems (MEMS) -based, fast-response, multi-sensor pressure probes of miniature size for velocity and pressure measurement applications in unsteady and turbulent flow gelds is also discussed. A new type of pressure sensor has been developed with silicon-nitride diaphragm and a characteristic size of only 250 gm. These pressure sensors are small enough to be mounted close to the surface of a miniature hemispherical-tip probe, obtaining a probe bandwidth and a theoretical frequency response up to 100 kl-lz. Both computational and experimental approaches are employed to develop calibration techniques suitable for highly unsteady flow environments with strong spatial gradients.