Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session NN: Supersonic and Hypersonic Flows |
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Chair: Lawrence Ukeiley, University of Florida Room: Salt Palace Convention Center 251 B |
Tuesday, November 20, 2007 11:35AM - 11:48AM |
NN.00001: A monopropellant micro-propulsion device in low temperature co-fired ceramics Donald Plumlee, Amy Moll, Aaron Coulter, Judi Steciak, Ralph Budwig A planar nozzle constructed in Low Temperature Co-Fired Ceramics (LTCC) has been developed for use in micro-propulsion applications. Three converging-diverging supersonic nozzle configurations were developed and tested using the LTCC materials system. A typical nozzle had a throat .17 mm wide by .22 mm deep, an exit Mach number of 2.4, and a thrust of 0.25 N. An isentropic model was generated to determine nozzle throat and exit size and nozzle curvature was defined using a method of characteristics approach. Each nozzle was tested using a cold gas test stand at several pressures. The experimental thrust measurement was compared to several models. The isentropic model predicted the actual thrust to within 25{\%}, while 3D CFD with a Spalart-Allmaras (SA) turbulence model predicted the thrust to within 5.9{\%}. A schlieren visualization system was implemented to further validate the CFD results. The density gradient of the nozzle plume using the SA turbulence model matched the schlieren image of the shock locations in the nozzle exit plume. Additional testing was performed with hydrogen peroxide as a monopropellant being delivered to the nozzle through a LTCC, silver embedded catalyst chamber. [Preview Abstract] |
Tuesday, November 20, 2007 11:48AM - 12:01PM |
NN.00002: Shock induced separation: statistical link between shock motion and separated zone Pierre Dupont, Jean-Paul Dussauge, Jean-Fran\c{c}ois Debieve The interaction between an oblique shock wave impinging on a turbulent boundary layer at Mach number 2.3 is studied, for flow deviations of 8\r{ } and 9.5, which produce separation. Fluctuations of wall pressure are measured. The shock is strongly unsteady, with fluctuations at low frequency; in the separated zone, higher frequencies are measured, together with fluctuations in the shock frequency range. Measurements of coherence and phase shifts are made between the shock foot and points in the separated bubble. Strong coherence is found between these fluctuations, with a constant phase shift of \textit{$\pi $} for the 8\r{ } deviation; more complex behaviours are found for 9.5\r{ }. A simple static scheme, based on the properties of the measured time histories of wall pressure is proposed; it reproduces correctly the out of phase signals in the 8\r{ } case, and the level of fluctuations along the interaction in the shock frequency range. This is compared with measurements of other authors in compression ramp flows. Moreover, PIV measurements are used to illustrate the dependence between the separation breathings and the position of the shock. [Preview Abstract] |
Tuesday, November 20, 2007 12:01PM - 12:14PM |
NN.00003: Low frequency oscillations in shock/boundary layer interactions Suman Muppidi, Krishnan Mahesh Shock wave/boundary layer interactions are observed frequently in high--speed flight, and can significantly impact aerodynamic and thermal loads. The interaction is characterized by boundary layer separation, shock oscillation, shock--shock interaction and unsteadiness. The objective of our work is to use Direct Numerical Simulations to study the origin and behavior of low--frequency unsteadiness observed in shock wave/boundary layer interactions. Results from supersonic ramp flow and incident shock flow simulations will be presented. We will discuss the effects of Reynolds number and Mach number, and the importance of appropriate numerical technique, computational domain and mesh. [Preview Abstract] |
Tuesday, November 20, 2007 12:14PM - 12:27PM |
NN.00004: Influence of a Localized Roughness Element on Disturbance Amplification in a Laminar Boundary Layer at Ma=4.8 Olaf Marxen, Gianluca Iaccarino, Eric Shaqfeh Knowledge of heat load on the surface of vehicles (re-)entering a planetary atmosphere is important for heat-shield design. Prediction of laminar-turbulent transition is a key factor for the design. We carry out numerical simulations of a flat-plate boundary layer with and without localized roughness element (small hump). The compressible Navier-Stokes equations are solved for a calorically perfect gas. Small perturbations at a fixed frequency are triggered at the wall. Their downstream convective amplification is compared between flat-plate and hump case. The roughness element leads to increased disturbance amplification. Peak amplitude levels are reached in the vicinity of the hump. The effect of the roughness element seems similar to the effect of a shock impinging on a wall. The present study shall be extended to include high-temperature gas effects as well as three-dimensional disturbances (oblique waves). [Preview Abstract] |
Tuesday, November 20, 2007 12:27PM - 12:40PM |
NN.00005: Flow Structure of Supersonic Cavity Flow with and Without Control George Shumway, Michael Sheehan, Farrukh Alvi, Lawrence Ukeiley Supersonic flow over an open cavity is studied experimentally to examine the effects of control on the flow field. Detailed PIV measurements were acquired for a rectangular cavity with a ramped floor in a Mach 1.5 free stream flow at the AAPL at FSU. The measurements were acquired for both an uncontrolled case and a case where micro-jets were used at the leading edge of the cavity. The properties of the micro-jets (pressure, diameter and injection location) have been optimized and have been shown to significantly reduce the fluctuating surface pressure through out the cavity both in terms of peak and broadband levels. Examination of flow field properties shows significant differences in the distribution of turbulent energy and the recirculation velocities. Further examination of the PIV snapshots with the POD has yielded insight into some of the similarities and differences in the turbulent structure between the controlled and baseline configurations. The cases yielded nearly the same amount of energy in the dominant mode (16\% vs. 18\%) however there are significant differences in the spatial features of the modes. In this presentation we will present features of the controlled and baseline cases including a quantitative analysis of the differences between the POD modes from the two cases. [Preview Abstract] |
Tuesday, November 20, 2007 12:40PM - 12:53PM |
NN.00006: Computation of Hypersonic Shock Structure in Diatomic Gases with Rotational and Vibrational Relaxation Using the Generalized Boltzmann Equation Ramesh Agarwal, Felix Cheremisin, Rui Chen The paper describes the computational methodology for computing hypersonic non-equilibrium shock wave (SW) flows of diatomic gases such as Nitrogen and Oxygen using the Generalized Boltzmann Equation (GBE) at Knudsen numbers in transitional and rarefied flow regimes. In the GBE (similar to Wang-Chang Uhlenbeck equation (WC-UE)), the internal and translational degrees of freedom are considered in the framework of quantum and classical mechanics respectively. The computational framework available for the classical Boltzmann equation is extended by including both the rotational and vibrational degrees of freedom in the GBE. The whole problem that includes both the vibrational - translational (VT) and rotational - translational (RT) energy transfers is solved by applying a three-stage splitting procedure to the WC-UE. The three stages consist of free molecular transport, VT relaxation, and RT relaxation. Computations are performed for the shock structure at high Mach numbers accounting for both the vibrational and rotational excitations, and are compared with the available experimental data. [Preview Abstract] |
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