Comprehensive Design of Axisymmetric Wind Tunnel Contractions

Design charts for wind tunnel contractions are developed using an inviscid, incompressible flow analysis. A contour formed of two cubic arcs joined smoothly together was found to be a good choice for a wall shape. Therefore, it was selected as the basis for a one-parameter family of wall shapes, which was then investigated in detail. The design chart parameters are the maximum wall pressure coefficients at the inlet (as an indicator of the danger of separation at the inlet end) and at the exit (which is related to the exit velocity nonuniformity). For any choice of these two parameters the charts yield the shape parameter and the nozzle length for this particular family of shapes. The charts may be used to design nozzles with no local separation at the inlet, and with any desired exit velocity uniformity. When the two pressure coefficients are chosen so that separation at both ends is just avoided, the exit boundary layer thickness should be near its minimum.