Abstract
Selection criteria of optimal conditions for supersonic tests in a blowdown wind tunnel
Highlights
SUPERSONIC wind tunnels are important tools of experimental aerodynamics
It has been shown that the choices of the test conditions for supersonic tests in the T-38 blowdown wind tunnel are limited by several constraints
Mach number in the supersonic test section is limited to the range from 1.4 to 4 by the mechanical design of the wind tunnel, though some further limitations, imposed by the starting loads, the safety of the model and instrumentation, and the interference from the wall-reflected shock waves may exist for very slender models and models having large aerodynamic lift and control surfaces, for which the use of the transonic test section with perforated walls may be needed at Mach numbers below 1.5
Summary
SUPERSONIC wind tunnels are important tools of experimental aerodynamics. They are used to investigate high-speed-flow phenomena and determine such aerodynamic characteristics of flying vehicles that, with the current state of the art, cannot be determined computationally, or else, are too expensive to determine computationally. Wind tunnel capabilities are better regarding the tests of high-speed missiles: Reynolds numbers close to highaltitude flight values being achievable in the test (Table 3) and adjustable to a certain degree by variation of the model size It may be noted (Fig.4) that many other wind tunnel facilities in the world fare much worse than the T-38 in this regard, flight Reynolds numbers being achievable only in several largescale cryogenic facilities [3]. The tests [6,9] have shown that, in a supersonic flow, transition to turbulent boundary layer occurs at Reynolds number (based on transition length) of about 2×106 to 8×106, depending on the Mach number, turbulence level in the wind tunnel, etc This condition is met in the T-38 where the -minimum- Reynolds number for a typical model length of 1 m is of the order of 20×106 and the maximum one can be more than 100×106 (Fig.). Base pressure and base drag in the supersonic tests in the T-38 are not likely to be sensitive to the dissimilarity between the test and the flight Reynolds number
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