An examination of suitability of multi-hole pressure probe technique for skin friction measurement in turbulent flow

The problems of misalignment to flow direction and the need to drill a tapping hole on a measurement surface to obtain total and static pressures make the use of Preston probe in skin friction measurement in a turbulent flow a cumbersome task. The suitability of a multi-hole pressure probe in a non-nulling mode to overcome these problems was, therefore, investigated. The near-wall effect on multi-hole pressure probe readings was examined both experimentally and theoretically. The results indicate that the presence of the wall had negligible overall effect. Experiments were carried out in a pipe, on a flat plate and on a swept forward facing step to simulate one-, two-, and three-dimensional turbulent flows. The skin friction coefficient determined using the multi-hole pressure probe was found to have good agreement with published data. Since the technique is based on similarity principle with probe diameter as a characteristic parameter, it is expected that the method would be effective with probe geometries of different sizes provided that they are small enough to be submerged in the boundary layer and that their calibration coefficients are accurately determined.

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► Multi-hole pressure probe in turbulent skin friction measurement was successfully conducted to overcome problems of the Preston method of misalignment and the need to determine static pressure separately.
► The application of five-hole pressure probe in obtaining ΔPΔP appears to reduce the wall effect more than the Preston method.
► The wall effect has greater impact on pitch angle than yaw angle values obtained by multi-hole pressure probe.
► A theoretical error analysis indicated that the wall effect has negligible effect in ΔPΔP values obtained by multi-hole pressure probe.