Three-Dimensional Flows and Hypersonic Vehicles

Three-dimensional flow-field calculation was, for decades, a frustrat­ing impossibility. I recall colleagues in the 1960s who would have sold their children (at least they said) to be able to calculate three­dimensional flow fields. The number of grid points required for such cal­culations simply exceeded the capability of any computer at that time. With the advent of supercomputers, however, the practical calculation

of three-dimensional flow fields became realizable. Once again, NASA researchers led the way. The first truly three-dimensional flow calcula­tion of real importance was carried out by K. J. Weilmuenster in 1983 at the NASA Langley Research Center. He calculated the inviscid flow over a Shuttle-like body at angle of attack, including the shape and location of the three-dimensional bow shock wave. This was no small feat at the time, and it proved to the CFD community that the time had come for such three-dimensional calculations.[780]

This was followed by an even more spectacular success. In 1986, using the predictor-corrector method conceived by NASA Ames Research Center’s MacCormack, Joseph S. Shang and S. J. Scherr of the Air Force Flight Dynamics Laboratory (AFFDL) published the first Navier-Stokes calculation of the flow field around a complete airplane. The airplane

was the "X-24C,” a proposed (though never completed) rocket-powered Mach 6+ hypersonic test vehicle conceived by the AFFDL, and the calcu­lation was made for flow conditions at Mach 5.95. The mesh system con­sisted of 475,200 grid points throughout the flow field, and the explicit time-marching procedure took days of computational time on a Cray computer. But it was the first such calculation and a genuine watershed in the advancement of computational fluid dynamics.[781]

Note that both of these pioneering three-dimensional calculations were carried out for hypersonic vehicles, once again underscoring the importance of hypersonic aerodynamics as a major driving force behind the development of computational fluid dynamics and of the leading role played by NASA in driving the whole field of hypersonics.[782]