Abstract

A. KLEIN.2 It has been known for some considerable time that, in the absence of special means of flow control, op-timum diffusers have bell-shaped walls. Contours of this type follow from a variety of boundary-layer optimization principles, notably from the postulation that the flow should produce vanishing wall shear stress (for example Fernholz, reference [1] and Hackeschmidt, reference [2]), from a modification of this concept attributable to Huo (reference [3]) and from application of a special deceleration parameter proposed by Senoo and Nishi, reference [4]. In spite of the deficiencies of the boundary-layer methods used in these analyses, the neglect of the effect of turbulence level on flow behavior and of the effects of wall curvature on turbulence structure, the overall conclusion of these investigations is certainly correct: bell-shaped walls are optimum