Flow Measurement and Instrumentation 9 (1998) 153–158 Five-hole pressure probe analysis technique G.L. Morrison * , M.T. Schobeiri, K.R. Pappu Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123, U.S.A. Received 11 November 1997; received in revised form 17 June 1998; accepted 23 June 1998 Abstract A refined calibration technique is presented for five-hole pressure probes operating in the non-nulling mode. The four 3D cali- bration surface equations required to reduce data obtained from the probe are curve-fit using a 3D curve-fitting program. The relatively simple equations are quick and easy to use for data reduction. The shape of the 3D surfaces are useful in determining if a probe should not be used due to any machining abnormality or damage a probe has sustained. The contours can also be used to determine the range of flow angles a particular probe can measure.  1998 Elsevier Science Ltd. All rights reserved. Keywords: Pitot probe; Three dimensional; Calibration 1. Introduction Five-hole pressure probes are becoming more useful with the development of small inexpensive fast response pressure transducers, computer controlled traversing sys- tems, and computer based data acquisition and analysis. A schematic of the end of a five-hole pressure probe is presented in Fig. 1. The probe can be operated in two ways. The most simple in terms of data analysis is the nulling arrangement where the probe is mounted on a five degree of freedom traversing system and is oriented such that the X-axis is parallel to the flow ( and  are both zero). The center pressure tap, P 5 , then measures the stagnation pressure and the pressures in the four Fig. 1. Schematic of a generic five-hole pressure probe. * Corresponding author. Tel.: + 1 409-845 5414; Fax: + 1 409- 845 3081; e-mail: gmorrison@mengr.tamu.edu 0955-5986/98/$—see front matter  1998 Elsevier Science Ltd. All rights reserved. PII:S0955-5986(98)00023-5 outer tubes are equal (P 1 = P 2 = P 3 = P 4 ) and pro- portional to the static pressure. This nulling technique requires a very sophisticated traversing system and long data acquisition time since the probe must be pitched and yawed at each measurement location until the four pressures are equal. This can take a long time, especially if the probe is small and has a slow time response. This paper will address the non-nulling technique in which the pressure probe undergoes an extensive calibration which is then used to determine the magnitude and direc- tion of the flow with respect to the coordinates of the probe. The non-nulling technique is performed by setting the probe at constant pitch and yaw values with respect to the test section, traversing the probe over the flow field, and measuring the five pressures at each measure- ment location. From these five measured pressures, the direction and magnitude of the flow with respect to the X-axis of the pressure probe are determined There is a maximum angle the flow can make with respect to the axis of the probe beyond which the flow separates from the probe. When this occurs the data cannot be reduced to obtain the velocity since the pressure taps in the separ- ated regions do not vary significantly nor monotonically with flow angle. Most data analysis techniques for the non-nulling operation of the probe require that the pro- bes are manufactured to exacting tolerances such that the response in each of the four pressure taps around the perimeter of the probe (P 1 , P 2 , P 3 , and P 4 ) is completely symmetrical. The objective of this work is to present a