Straight-walled, two-dimensional diffusers of large aspect ratio were investigated experimentally for the purpose of studying the regime of incipient transitory stall, the location of the geometry of peak diffuser pressure recovery. Twelve symmetric diffusers of constant nondimensional length (L/W1 = 15) with total included angles ranging from 4 to 24 degrees, covering attached, intermittently detaching, and unsteady detached flows were examined. Tests were run at one inlet blockage, 2δ1 / W1 = 0.027, and at an inlet Reynolds number of U1 W1/ν = 2.2 × 105 with air flow at low inlet Mach number. Pressure recovery and flow direction intermittency were obtained along the diffuser walls. An objective comparison of the UIM method of Ghose and Kline and an improved prediction method [Appendix] was performed with respect to these new experimental data. Some new conclusions are drawn concerning the nature of the flow in the vicinity of peak pressure recovery.

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