Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session R24: Compressible Flows II |
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Chair: Joanna Austin, University of Illinois at Urbana-Champaign Room: 30E |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R24.00001: Planar Reflection of Detonations Waves Jason Damazo, Joseph Shepherd An experimental study examining normally reflected gaseous detonation waves is undertaken so that the physics of reflected detonations may be understood. Focused schlieren visualization is used to describe the boundary layer development behind the incident detonation wave and the nature of the reflected shock wave. Reflected shock wave bifurcation--which has received extensive study as it pertains to shock tube performance--is predicted by classical bifurcation theory, but is not observed in the present study for undiluted hydrogen--oxygen and ethylene--oxygen detonation waves. Pressure and thermocouple gauges are installed in the floor of the detonation tube so as to examine both the wall pressure and heat flux. From the pressure results, we observe an inconsistency between the measured reflected shock speed and the measured reflected shock strength with one dimensional flow predictions confirming earlier experiments performed in our laboratory. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R24.00002: Shock-boundary layer interaction and transonic flutter Pradeepa Tumkur Karnick, Kartik Venkatraman The transonic flutter dip of an aeroelastic system is primarily caused by compressibility of the flowing fluid. Viscous effects are not dominant in the pre-transonic dip region. In fact, an Euler solver can predict this flutter boundary with considerable accuracy. However with an increase in Mach number the shock moves towards the trailing edge causing shock induced separation. This shock-boundary layer interaction changes the flutter boundary in the transonic and post-transonic dip region significantly. We discuss the effect of viscosity in changing the flutter boundary in the post-transonic dip region using a RANS solver coupled to a two-degree of freedom model of the structural dynamics of a wing. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R24.00003: Detailed Simulations and Analysis of Shock Bifurcation Yong Sun, Matthias Ihme, Ralf Deiterding The interaction between the reflected shock wave and the boundary layer, that is formed by the incident shock, leads to shock bifurcation. This interaction induced inhomogeneities in the flow-field behind the reflected shock, and thereby affecting the combustion process in shock-tube ignition studies. To quantify effects of shock-bifurcation on the region behind the reflected shock, detailed simulations of a shock-tube system at high-pressure conditions are performed under consideration of detailed hydrogen reaction chemistry. Both 2D and 3D simulations are performed, and simulation results are compared against experiments and low-order shock-bifurcation models. To isolate relevant physical processes, additional simulations for different operating conditions, mixture-compositions, and adiabatic and isothermal walls are conducted, and results of this investigation are discussed in this presentation. [Preview Abstract] |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R24.00004: Investigation of a transonic axisymmetric backward-facing step flow by means of time-resolved PIV and PSP Sven Scharnowski, Martin Bitter, Christian J. K\"ahler The results presented here are obtained within a sub project of the SFB TRR 40 program (founded by the German research foundation), which focuses on the analysis and modeling of coupled liquid rocket propulsion systems and their integration into the space transportation system. The overall objective is to develop technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems. The interaction between the shear layer and the nozzle in the wake of the launcher is particularly important. Therefore, detailed analyses of a generic space launcher model's wake flow are the main emphasis of this sub project. The combination of time-resolved PIV and PSP provide deep insights into the flow physics: The separation at the end of the main body, the formation of the shear layer, its growth and its reattachment, as well as the surface pressure fluctuations, are analyzed in detail. The results reveal unsteady loads caused by shear layer motion which could interfere with structural modes of a space launcher main engines' nozzle. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R24.00005: Evolution of Imposed Vortices Over Concave Surfaces in Hypervelocity Flow William Flaherty, Joanna Austin Steamwise oriented vortices in the boundary layer of a hypersonic flow have the potential to affect heat transfer and skin friction significantly. These effects can be exacerbated by the addition of extra strain rates associated with concave surface curvature. Vortices can either occur naturally (in the form of Goertler vortices), or be introduced by some form of mechanical distortion (such as a protuberance). In this work we experimentally investigate the effect of concave surface curvature on the propagation of imposed vortices. These experiments are carried out in the Hypervelocity Expansion Tube at the University of Illinois. This facility is capable of generating flows with high enthalpies (4-9MJ/kg) and Mach numbers (3-7). Using a novel, fast-response pressure sensitive paint we are able to observe the development of vortices which are induced using diamond-shaped vortex generators. Models with varying amount of surface curvature (encompassing Goertler numbers between 10-22) are used to investigate the dynamics of vortex propagation and interaction. Our results show that the vortices remain attached and of constant strength for 10-12cm (80 boundary layer thicknesses) along the curved surfaces, while on flat plates the vortices are no longer apparent within 6 cm downstream. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R24.00006: Shock focusing in water by convergent shell structures Chuanxi Wang, Veronica Eliasson Lab scale experiments on shock focusing in water in convergent thin shell structures have been designed and performed. Thin shell structures made of two types of materials have been tested separately; carbon fiber and low carbon steel. The geometric shape of the structures is given by a logarithmic spiral, which is believed to maximize the amount of energy reaching the focal region from previous research. During an experiment, a shock wave in water is generated by projectile impact. High-speed schlieren photography is applied simultaneously to visualize the shock dynamics during the focusing event. Results show that the thin shell structure and the shock wave in the water are fully coupled and the interaction has some unique features, such as wave train patterns in water. [Preview Abstract] |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R24.00007: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2012 2:31PM - 2:44PM |
R24.00008: Nitric oxide emission spectroscopy measurements in a hypervelocity post-shock flow field Andrew Swantek, Joanna Austin In hypervelocity flight conditions, typical of sub-orbital and reentry trajectories, the coupling between the fluid mechanics and the thermochemistry of the flow becomes important. In the current work, we use an expansion tube facility to accelerate air to hypervelocity test conditions (stagnation enthalpy 8MJ/kg, velocity 3.8 km/s). A double wedge model is used to generate an oblique shock, a strong bow shock, and a shock-boundary-layer interaction which is known to be very sensitive to the thermochemical state of the gas. We investigate the nitric oxide emission signal in the ultraviolet region (220-255 nm, A-X transition) at four spatial locations downstream of the bow shock (0, 2, 4, and 6 mm). An in-house code is used to simulate the spectrum in this region and thus obtain a temperature fit. Temperatures are observed to decrease when traversing downstream, starting at approximately the frozen temperature (about 7700 K) at the location of the shock (0 mm). The furthest downstream point deviates from this trend, potentially due to heating in a shear layer formed in the flow field. The flow field is seen to be in non-equilibrium in this region, as temperatures do not reach the equilibrium temperature (about 3900 K). [Preview Abstract] |
Tuesday, November 20, 2012 2:44PM - 2:57PM |
R24.00009: Shock Tube Investigation of Quasi-Steady Drag in Shock-Particle Interactions Justin Wagner, Steven Beresh, Sean Kearney, Brian Pruett, Elton Wright A reassessment of historical drag coefficient data for spherical particles accelerated in shock-induced flows has motivated new shock tube experiments of particle response to the passage of a normal shock wave. Particle drag coefficients were measured by tracking the trajectories of 1-mm spheres in the flow induced by incident shocks at Mach numbers 1.68, 1.93, and 2.04, over test times of about 0.5 milliseconds. Previous shock tube studies conducted under similar test conditions have concluded that the unsteadiness associated with the accelerating particle resulted in elevated drag coefficients. However, recent theoretical work suggests that such effects should only last for microsecond timescales. Furthermore, low values for the acceleration parameter indicate that unsteadiness should be negligible. Consistent with past experiments, the current data clearly show that as the Mach number increases, the drag coefficient increases substantially. This increase significantly exceeds the drag predicted by incompressible standard drag models, but a recently developed compressible drag correlation returns values quite close to the current measurements. Consistent with recent theoretical work, these observations suggest that elevated particle drag coefficients are a quasi-steady phenomenon attributed to increased compressibility rather than true flow unsteadiness. [Preview Abstract] |
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