Turbulent mixing in adapted and weakly underexpanded (underexpansion ratios less than 1.4) round jets, involving fully developed pipe flows injected into still air, was studied experimentally. Measurements included mean and fluctuating concentrations and mean static pressures using laser-induced iodine flourescence and mean and fluctuating streamwise velocities using laser Doppler anemometry. Predictions were used to help interpret the measurements and to initiate evaluation of methods for analyzing these processes. The predictions were based on k-e turbulence models, including a proposed extension to treat compressibility effects at high convection Mach numbers. In conjunction with other measurements, the results show that the near-field region of underexpanded jets is influenced by compressibility, which tends to reduce turbulent mixing rates at high convective Mach numbers, and high turbulence levels at the jet exit, which tends to increase turbulent mixing rates. Predictions based on effective-adapted-jet exit conditions yielded reasonably good estimates of mixing levels near the exit of underexpanded jets for both fully developed and slug flow jet exit conditions; however, such methods provide no information concerning the near-field region containing the shock waves. Predictions based on solution of parabolized Navier-Stokes governing equations, using the SCIPVIS algorithm, were encouraging for slug flow exit conditions, but this approach must be extended to treat fully developed flow at the jet exit. Nomenclature a = acceleration of gravity C M = constant in turbulence model d =jet exit diameter / = mixture fraction Fr = Froude number k -turbulence kinetic energy K = compressibility correction M = Mach number M c = convective Mach number p = static pressure r = radial distance u = streamwise velocity x = axial distance e = rate of dissipation of turbulence kinetic energy H t = turbulent viscosity v = kinematic viscosity Subscripts c = centerline quantity e =jet exit condition oo = ambient condition Superscripts(")(")' = time-averaged mean and root-mean-squared fluctuating quantity
