关键词: 低速风洞, 收缩段, 数值计算, 设计

Abstract:

The numerical analysis of the incompressible flow in rectangular contractions is performed, by using a finite-difference method and body-fitted coordinates. Three types of commonly used wall contours are chosen and compared, i.e. contour with Witozinsky curve, 5th power curve and match cubic curves respectively. Two design criteria have been generally used for axisymmetric contractions, i.e., (1) no separation on nozzle walls, (2) non uniformity at exit cross section lower than 2%. These criteria are revised and applied to three-dimensional contractions to compare the performance of the above mentioned three types of contours. It is found that the contour with matched cubic curves, when optimized, gives the most satisfactory results, while the contour with Witozinsky curue gives the worst results because of serious adverse pressure gradient near the entrance. Some problems of three -dimensional contraction design are also discussed. The cross section similarity is usually considered as a requirement in three- dimensional contraction design practice. The author's numerical investigation shows, however, that this requirement is of no real value.

Key words: Low speed wind tunnel, Contractors, Numerical calculation, Design