MICROCOMPUTER BASED CONTROL OF A LARGE CRYOGENIC WIND TUNNEL

PROOF OF CONCEPT DEMONSTRATION, OF THE 0.3 M TRANSONIC CRYOGENIC WIND TUNNEL IN EARLY 1970'S, HAS PAVED WAY FOR LARGE HIGH REYNOLDS NUMBER CRYOGENIC TUNNEL LIKE THE NATIONAL TRANSONIC FACILITY (NTF) IN 1984. THE QUALITY OF DATA GENERATED IN A CRYOGENIC TUNNEL IS INTIMATELY RELATED TO THE STABILITY OF THE TUNNEL TEST SECTION FLOW STATES VIZ,STAGNATION PRESSURE, TUNNEL GAS TEMPERATURE AND FLOW MACH NUMBER. THE TUNNEL FLOW STATE DYNAMICS IS HIGHLY NONLINEAR AND COUPLED RELATIVE TO THE INPUTS USED FOR CONTROLLING THE TUNNEL. THE 0.3 M TRANSONIC CRYOGENIC TUNNEL AT LANGLEY RESEARCH CENTER HAS BEEN OPERATIONAL FOR NEARLY 14 YEARS OF WHICH IT HAS BEEN UNDER CLOSE LOOP CONTROL FOR EIGHT YEARS. RECENTLY THE 0.3 M TCT HAS BEEN BROUGHT UNDER FULL CONTROL OF A 16 BIT MICROCOMPUTER TO REALIZE TEMPERATURE STABILITY OF +/-0.15 K, REYNOLDS NUMBER TO +/-0.03 MILLION AND MACH NUMBER TO +/-0.002. THE CONTROL ANALYSIS USED HAS BEEN A LUMPED PARAMETER APPROACH AND MECHANIZATION OF THE CONTROL LAW IS THROUGH USE OF STANDARD COMMERCIAL MICROCOMPUTER HARDWARE WITH FLEXIBLE SOFTWARE WRITTEN IN A HIGH LEVEL REAL TIME LANGUAGE. THE AIM OF THIS PROPOSAL IS TO APPLY LUMPED PARAMETER CONTROL TECHNIQUES, AND MICROCOMPUTER SOFTWARE BASED MECHANIZATION OF CONTROL LAWS TO THE NATIONAL TRANSONIC FACILITY. SPECIFICALLY, DEMONSTRATION OFTEMPERATURE IS PROPOSED.