This report describes the calibration of a non-nulling, conical, seven-hole pressure probe over a large range of flow onset angles. The calibration procedure is based on the use of differential pressures to determine the three components of velocity. The method allows determination of the flow angle and velocity magnitude to within an average error of 1.0° and 1.0% respectively. Greater accuracy can be achieved by using high quality pressure transducers. Also included is an examination of the factors which limit the use of the probe, a description of the measurement chain, an error analysis, and a typical experimental result. In addition, a new general analytical model of pressure probe behavior is described and the validity of the model is demonstrated by comparing it with experimentally measured calibration data for a three-hole yaw meter and a sevenhole probe.

Modelling, calibration, and error analysis of seven-hole pressure probes

A non-nulling seven-hole conical pressure probe capable of measuring flow conditions at angles up to 75 deg relative to its axis is described. The theoretical rationale of the seven-hole probe is developed and the calibration procedure outlined. Three-variable third-order polynomial functions are used to represent local values of relative flow angles, total pressure, and total minus static pressure. These flow properties are determined explicitly from measured probe pressures. Flow angles are determined within 2.5 deg and Mach number within 0.05 with 95% certainty. The probe can be used in subsonic compressible and incompressible flows.

Seven-hole cone probes for high angle flow measurement Theory and calibration

This paper illustrates a method for calibrating seven-hole probes to measure local total and static pressures and relative flow angles of up to 70 degrees in subsonic compressible flows. The method of Latin Squares was used to statistically sample a large and otherwise unmanageable data set, thereby reducing to a minimum the number of data points required to construct a polynomial curve fit to the data. Calibration produces three-variable third order polynomials which permit all of the desired flow properties to be found explicitly from probe measured pressures. This method determines the flow angles to within 2 degrees and Mach number to within 0.04 with 95 percent certainty.

Non-nulling seven-hole probes for high angle flow measurement

A two-step calibration and measurement procedure for seven-hole pressure probes has been developed that allows simple and accurate real-time processing. The method adds an extra step to traditional least-squares calibration schemes such as Gallington’ s method (Gallington, R. W., “ Measurement of Very Large Flow Angles with Non-Nulling Seven Hole Probes,”Proceedings of the 27th International Instrumentation Symposium , Instrumentation Society of America, Triangle Park, NC, 1981, pp. 115 ‐130)involving the interpolation of error look-up tables. A measurement system employing the two-step calibration scheme is described. Measurements are made in pipe and wind-tunnel e ows, and a detailed uncertainty analysis is performed, to demonstrate the accuracy of the new scheme. Independent of the new scheme, the measurements also show some effects of Reynolds number, velocity gradient, and turbulenceon theprobeaccuracy. TheReynoldsnumbereffect was notanticipated and may indicate the need for multiple calibrations in some circumstances.

Seven-Hole Pressure Probe Calibration Method Utilizing Look-Up Error Tables

A Comparison of Data-Reduction Methods for a Seven-Hole Probe

This paper describes a method for measuring local direction and total and static pressures of a flow by means of a fixed probe, provided that the local air flow does not make an angle of more than 80 degrees with the axis of the probe. The probe is easily manufactured from standard-sized tubing materials. The power series calibration method used with the probe results in explicit polynomial expressions for the desired aerodynamic properties. The calibration method is easily programmed on a data acquisition system. This paper includes an example of a complete incompressible calibration.

R. W. Gallington

Papers

Measurement of very large flow angles with non-nulling seven-hole probes