Peculiarities of the flows forming in processes of an impulse starting of a supersonic wind tunnel with different diffusers

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The peculiarities of supersonic unsteady flows forming in the processes of an impulse starting of a wind tunnel including a fore-chamber, a nozzle, a diffuser, and an exhaust tank are considered. The fore-chamber is separated from the flow duct by a thin breakable diaphragm. Before the wind tunnel starting, the gas contained in the exhaust tank is pumped out down to a very small pressure, and then the high-pressured working gas is fed into the fore-chamber. Upon reaching some value of this pressure, the diaphragm “instantaneously” ruptures, and the working gas starts exhausting through the nozzle: a rapid unsteady process of the wind tunnel starting arises. The numerical simulation of the flows forming at the impulse starting of the simplest experimental gas-dynamic facility has been carried out; the facility is arranged with a nozzle forming at its exit a two-dimensional supersonic flow with the Mach number of 2.9, and with replaceable diffusers having different relative areas of the throat. The numerical computations of two-dimensional unsteady flows have been carried out using the Reynolds-averaged Navier—Stokes equations and the SST k-ω turbulence model. The flow patterns computed numerically are compared with the data of the optical visualization of the flow obtained in the experimental gas-dynamic facility in the process of its starting.