Browsing by Subject "Supersonic"
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Item Acoustic waveforms produced by a laboratory scale supersonic jet(2014-08) Fiévet, Romain; Tinney, Charles Edmund, 1975-The spatial evolution of acoustic waveforms produced by a Mach 3 jet are investigated using both 1/4 inch and 1/8 inch pressure field microphones located along rays emanating from the post potential core where the peak sound emission is found to occur. The measurements are acquired in a fully anechoic chamber where ground, or other large surface reflections are minimal. The calculation of the OASPL along an arc located at 95 jet diameters using 120 planar grid measurements are shown to collapse remarkably well when the arc array is centered on the post potential core region. Various statistical metrics, including the quadrature spectral density, number of zero crossings, the skewness of the pressure time derivative and the integral of the negative part of the quadrature spectral density, are exercised along the peak emission path. These metrics are shown to undergo rapid changes within 2 meters from the source regions of this laboratory scale jet. The sensitivity of these findings to both transducer size and humidity effects are discussed. A visual extrapolation of these nonlinear metrics toward the jet shear layer suggests that these waveforms are initially skewed at the source. An experimentally validated wave packet model is used to confirm the location where the pressure decay law transition from cylindrical to spherical. It is then used to estimate the source intensity, which is required to predict the effective Gol'dberg number.Item Development of scalar and velocity imaging diagnostics for supersonic hypermixing strut injector flowfields(2014-12) Burns, Ross Andrew; Clemens, Noel T.A new diagnostic technique for studying the turbulent mixing characteristics of supersonic mixing flowfields is developed and implemented in two Mach 3 mixing flowfields. The diagnostic utilizes simultaneous particle image velocimetry and quantitative planar laser-induced fluorescence of krypton gas to study the interaction between turbulent scalar and velocity fields. The fluorescence properties of krypton gas are determined; measurements of the pressure and temperature dependence of the collisional quenching rates and cross-sections are made for various mixtures with krypton. The gases tested in this fashion include helium, nitrogen, air, oxygen, and ethylene. Additional measurements are performed to measure the relative two-photon absorption cross-section for krypton gas. The non-dimensional quenching rates are found to follow a power-law dependence for temperature, while the pressure dependence of the total quenching rate is found to be linear. Two injection flowfields are studied for their general topology and kinematic characteristcs. The first injector model is a basic injector meant to serve as a baseline case; there are no hypermixing elements present in this model. The second model is an asymmetric, unswept hypermixing injector featuring 15 degree expansive ramps flanking a central block. These studies utilize particle image velocimetry in planar and stereoscopic configurations in various planes. Results for the mean flowfield show distinct differences between the two flowfields; the planar injector flowfield is shown to be highly two-dimensional and exhibits minimal coherent unsteady behavior. The hypermixing injector flowfield exhibits a highly three-dimensional wake, with a pair of stream-wise vortices driving both mean deviations in the flowfield and considerable vortical coupling in the span-wise direction. Simultaneous krypton PLIF and PIV are employed in the two mixing flowfields. An assay of the dependence of the krypton mole fraction calculations on the fluorescence signal is performed. The overall sensitivity and the resulting dynamic range of the calibration is dictated largely by the reference mole fraction. Additionally, several different theoretical models of the temperature dependence of the fluorescence signal are studied to assess their validity and influence over the PLIF calibration procedure. Finally, the technique is employed in the two mixing flowfields, and a brief analysis of the mean and unsteady behavior of the two is conducted.Item Rotational and Vibrational Raman Spectroscopy for Thermochemistry Measurements in Supersonic Flames(2013-05-31) Bayeh, Alexander CHigh speed chemically reacting flows are important in a variety of aerospace applications, namely ramjets, scramjets, afterburners, and rocket exhausts. To study flame extinction under similar high Mach number conditions, we need access to thermochemistry measurements in supersonic environments. In the current work a two-stage miniaturized combustor has been designed that can produce open supersonic methane-air flames amenable to laser diagnostics. The first stage is a vitiation burner, and was inspired by well-known principles of jet combustors. We explored the salient parameters of operation experimentally, and verified flame holding computationally using a well-stirred reactor model. The second stage of the burner generates an external supersonic flame, operating in premixed and partially premixed modes. The very high Mach numbers present in the supersonic flames should provide a useful test bed for the examination of flame suppression and extinction using laser diagnostics. We also present the development of new line imaging diagnostics for thermochemistry measurements in high speed flows. A novel combination of vibrational and rotational Raman scattering is used to measure major species densities (O_2, N_2, CH_4, H_2O,CO_2, CO, & H_2) and temperature. Temperature is determined by the rotational Raman technique by comparing measured rotational spectra to simulated spectra based on the measured chemical composition. Pressure is calculated from density and temperature measurements through the ideal gas law. The independent assessment of density and temperature allows for measurements in environments where the pressure is not known a priori. In the present study we applied the diagnostics to laboratory scale supersonic air and vitiation jets, and examine the feasibility of such measurements in reacting supersonic flames. Results of full thermochemistry were obtained for the air and vitiation jets that reveal the expected structure of an under-expanded jet. Centerline traces of density, temperature, and pressure of the air jet agree well with computations, while measurements of chemical composition for the vitiation flow also agree well with predicted equilibrium values. Finally, we apply the new diagnostics to the exhaust of the developed burner, and show the first ever results for density, temperature, and pressure, as well as chemical composition in a supersonic flame.