Measurement of flow direction in a shear flow

Measurements of the flow direction error of some accepted designs of combination pressure-sensing probes in a shear flow have been made. For a spherical probe an inviscid shear flow theory predicts the flow direction error with good accuracy for normal hole spacing, namely 65-85 degrees , but becomes less accurate at much larger hole spacing (about 110 degrees ). The problem of determining the direction of the free shear jet used for testing was solved by measuring the apparent flow direction with several sizes of geometrically similar probes and extrapolating to zero size for the true direction. An important observation of error in the use of a parallel hot-wire probe in a shear flow has been made.