Moving ground simulation by tangential blowing

Belt-type moving-ground equipment, used for ground-effect simulation in STOL and VTOL tests, can be inconvenient and costly, especially in large tunnels. In most cases, such difficulties may be avoided by employing tangential blowing from a single slot at the ground surface. The paper reviews several powered model tests using both moving-ground and tangential blowing and describes the slot configuration and test techniques which were developed. Ground skin friction is monitored to set blowing levels and no model-depende nt calculations are needed. It is also shown that application to center-tunnel testing can delay tunnel flow breakdown considerably. Nomenclature b - base model wing span BLC = boundary-layer control c = nominal wing chord CL = lift coefficient, based on S Cm = pitching moment coefficient, based on S, about wing quarter chord Cp - static pressure coefficient, (p —p0) /q C = momentum coefficient, based on S H = total pressure H0 = mainstream total pressure h = model height above ground plane p = local static pressure P0 = effective static pressure at model station S - wing area U^ = freestream velocity X = distance measured axially downstream from model wing quarter chord y = distance measured laterally from tunnel centerline OLT - angle of attack at tailplane, relative to fuselage axis Aa =otT increment between blown- and moving-ground conditions d* = boundary-layer displacement thickness r; = spanwise station 2y/b