On the calculation of boundary-layer parameters from discrete data

Abstract

An investigation of the errors inherent in the calculation of integral boundary-layer parameters from discrete datasets has been carried out. The primary errors examined were those due to discretization of the velocity profile, distance of the first data location from the wall, and uncertainty in the floor location. A range of turbulent velocity profiles with different shape factors from analytical models and published DNS investigations has been examined. This analysis demonstrates that the spacing of the first measurement point from the floor is by far the most critical error source. Furthermore, the error is shown to be a function of boundary-layer shape factor, and therefore, a correction factor chart has been derived. Two alternative methods of estimating integral boundary-layer parameters have been examined: wall modeling and a gradient-based formulation. These have both been shown to generate smaller errors than the basic integration approach, although both are susceptible to external influences.