DESIGN OF SWIRL SIMULATORS

Response of turbo-jet engines to the swirling flow at engine face has recently been a matter of major concern, and this response can only be evaluated on the testbed with the help of swirl simulators. A method for design of such simulators is presented. Swirl blades that generate wake vortices are installed on the inner surface of the air inlet. As the arrangement of blades may vary in blade number and circumferential position, as well as in blade geometry and angle of attack, there is no want of factors by which the characteristics of the flowfield can be controlled. It is assumed that the wake vortices are well formed at the cross section of the duct corresponding to the trailing edges of the blades. The structure and positions of these vortices have to be determined, the flowfield at this cross section can then be computed. Since the velocities ofthe vortex centers are known, their respective positions at a nearby section slightly downstream can be determined. The flowfield at this new section can then be computed. Thus,the computation goes on step by step from the blade section up to the final section where the desired flow pattern is to be obtained. The design work begins with a tentative choice of blade arrangement. Comparison of computation with the desired result will guide the modification of blade arrangement. A computer, which displays a new flow pattern each time a correction is made of the blade arrangement, greatly facilitates the design work. Swirl patterns given in the literature of real aircraft inlets have been simulated by this method and test results are shown to be satisfactory.