COUPLING OF UNSTEADY FLUID DYNAMICS AND STRUCTURE IN LOW DENSITY HIGH SPEED FLOWS

AN INNOVATIVE COMPUTATIONAL TECHNIQUE IS REQUIRED TO COUPLE A COMPRESSIBLE TIME-ACCURATE CFD CODE WITH A STRUCTURAL ANALYSIS CODE TO SIMULATE FLUIDS-STRUCTURES INTERACTION. A LITERATURE SURVEY SHOWS THAT SOME INVESTIGATIONS HAVE BEEN MADE FOR FLUIDS-STRUCTURES COUPLING IN TRANSONIC FLOW, BUT ALMOST NO SIGNIFICANT DEVELOPMENTS EXIST FOR THE LOW-DENSITYHYPERSONIC FLOW REGIME. NASA HAS BEEN REVIEWING A CLASS OF LIGHTWEIGHT, UMBRELLA-TYPE ELASTIC AOTVS TO OPERATE AT HIGH MACH NUMBERS IN THE LOW-DENSITY REGION OF THE ATMOSPHERE. THE PAYLOADS WHICH ARE MOUNTED IN THE WAKE REGION OF THE AEROBRAKE WILL BE SUBJECT TO IMPINGEMENT OF THE SHEAR LAYER SEPARATING FROM THE AEROBRAKE. THE SHEAR LAYER WILL BE UNSTEADY, THUS INDUCING TIME-DEPENDENT AERODYNAMIC LOADS THAT WILL EXCITE AEROELASTIC STRUCTURAL MOTION. THIS MOTION, IN TURN, CAN EXCITE UNSTEADINESS OF THE SHEAR LAYER. THUS, CYCLIC VARIATIONS IN THE AERODYNAMICS AND AEROHEATING OF THE AEROBRAKE, AND SHEAR LAYER IMPINGEMENT ON THE PAYLOAD WILL EXIST. IF THESE OSCILLATIONS ARE NOT STABLIZED, AEROTHERMAL AND/OR STRUCTURAL FAILURE MAY OCCUR. IT IS PROPOSED, THEREFORE, TOCONDUCT A LITERATURE SURVEY FOR COMPRESSIBLE TIME-DEPENDENT FLOW, CHOOSE A SUITABLE STRUCTURAL RESPONSE CODE AND DEVELOPA COUPLING PROCEDURE INCLUDING A MOVING GRID ALGORITHM AND TIME-STEP CALCULATION PROCEDURE.