Skin friction measurements by laser interferometry in swept shock/boundary-layer interactions

Abstract

Measurements have been made of wall shear stresses in swept interactions of planar shock waves generated by a sharp fin and the two-dimensional turbulent boundary layer on a flat plate. Test conditions were Mach number 3.03, Reynolds number Re e -1.5 X 10 4 , wall temperature near adiabatic, and fin angles of 10 and 16 deg. Measurements were made using the Laser Interferometer Skin Friction (LISF) meter, which optically detects the thickness of an oil film on the test surface. The results show that such measurements are practical in high-speed interacting flows with a repeatability of ± 12% or better. Further, with proper data handling, LISF measurements appear feasible at very high shear levels, which were previously considered unobtainable. Dramatic increases in wall shear were observed in both swept interactions tested. These data are compared with computational Navier-Stokes solutions by Horstman and Knight wherein k-e and algebraic turbulence models were used. Both computations predict the overall measured c/ levels at a = 10 deg but fail to predict some features of the Cf distributions properly. Nomenclature c f = skin friction coefficient based on incoming freestream conditions MO, = incoming freestream Mach number N = number of fringes Po = stagnation pressure of incoming stream, MPa (psia) p w = wall static pressure on flat plate, MPa (psia) /?oo = incoming freestream static pressure, MPa (psia) R = radial distance measured from the fin leading-edge, cm (in.) ReQ= Reynolds number based on the local, undisturbed boundary-layer momentum thickness 5 = distance measured along surface streamline, mm T aw = adiabatic wall temperature, K T 0 = freestream stagnation temperature, K T w = wall temperature, K u + ,y + = dimensionless wall-wake velocity and height coordinates x,y,z = orthogonal stream wise, normal, and span wise coordinates, respectively, cm a.= angle made by fin with respect to the incoming freestream direction, deg /3 = angle with respect to freestream direction, measured from fin leading edge, deg As = distance from oil-film leading edge to laser spot along surface streamline, mm 5 = local, undisturbed boundary-layer thickness, mm v = oil viscosity, cs II = boundary-layer, wake-strength parameter T W = wall shear stress, N/m 2 Subscripts is = incident shock wave location ps = primary separation line location r = reattachment line location 5-5 = secondary separation line location ui = upstream influence line location

Quasiconical free interaction between a swept shock and a turbulent boundary layer

“…The reason is that along a given ray from the virtual origin, i.e., with (3 = const, the surface streamline at the radial distance will have arrived there from the attachment line after traversing a shorter distance than a surface streamline at a farther distance away. Thus, experiments by Kim and Settles 7 and computations by Knight and Badekas 5 showed a steady rise of skin friction coefficient with r and a leveling off which occurs somewhat later than expected from inception length data obtained through surface flow visualization. 6 The basis for this nonconical behavior of properties involving derivatives of pressure, velocity, or temperature is explained in Courant and Friedrichs.…”

A reflection-type oil-film skin-friction meter

“…Most of these have been performed at Ames Research Center (Monson and Higuchi 1980;Monson 1983;Monson 1984;Westphal et al 1986;Murphy and Westphal 1986). Very recently, the method has been extended by Kim and Settles (1990) to very high % (about 600 N/m 2) levels. These contributions have improved the accuracy and objectivity in the use of the method.…”

“…3 a, b) measurements Experiments in Fluids 11 (1991) having a population of 5, a similar uncertainty of about + 5% was achieved with both Preston tubes and the interferometric version of the oil-film meter. Kim and Settles (1990) on the other hand, have achieved a repeatability (_+ ~r error band, where r is standard deviation) of _+ 12% in high speed compressible flows. (In comparison, in the improved version of the present method, two third of the measurements (within ___ ~r) have a repeatability of __ 10%).…”

Luminescent Oil-Film Skin-Friction Meter

“…The laser interferometer was further improved by Monson and Higuchi 4 and Kim and Settles. 5 The image-basedglobal interferometer was developed by Monson et al, 6 Naughton and Brown, 7 and Zilliac. 8 In addition to these interferometric methods, Bandyopadhyayand Weinstein 9 developeda re ection-typeoil-lm meter.…”