Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session G25: General High Speed Flows and Boundary LayersBoundary Layers Compressible
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Chair: Arman Mirhashemi, University of Notre Dame Room: 705 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G25.00001: Introducing a nano-scale crossed hot-wire for high Reynolds number measurements Yuyang Fan, Matthew Fu, Janik Kiefer, Marcus Hultmark Hot-wire anemometry is commonly used for high Reynolds number flow measurements, mainly because of its continuous signal and high bandwidth. However, measuring two components of velocity in high Reynolds number wall-bounded flows has proven to be quite challenging with conventional crossed hot-wires, especially close to the wall, due to insufficient resolution and obstruction from the probe. The Nano-Scale Thermal Anemometry Probe (NSTAP) is a miniature hot-wire that drastically increased the spatial and temporal resolutions for single-component measurements by using a nano-scale platinum wire. Applying a novel combining method and reconfiguration of the NSTAP design, we created a sensor (x-NSTAP) that is capable of two-component velocity measurements with a sensing volume of approximately $50\times50\times50\mu$m and a temporal resolution approximately one order of magnitude faster than a conventional hot-wire. The x-NSTAP is characterized and deployed in the Princeton Superpipe facility for accurate measurements of the Reynolds stresses at very high Reynolds numbers. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G25.00002: Examination of uniform momentum zones in hypersonic turbulent boundary layers Owen Williams, Clara Helm, Pino Martin The presence of uniform momentum zones (UMZs) separated by regions of high shear is now well-established in incompressible flows, with the mean number of such zones increasing in a log-linear fashion with Reynolds number. While known to be present in supersonic and hypersonic boundary layers, the properties of these UMZs and the appropriate Reynolds number for comparison with incompressible results have not previously been investigated. A large, previously published DNS database of hypersonic boundary layers is used in this investigation, with Mach numbers up to 12 and wall temperatures from cold to adiabatic, resulting in a wide range of outer layer Reynolds numbers. UMZs are examined using a range of parameters in both conventional inner and semi-local scalings, and Reynolds number trends examined. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G25.00003: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 11:14AM - 11:27AM |
G25.00004: Schlieren image velocimetry measurements in a rocket engine exhaust plume Rudy Morales, Julio Peguero, Michael Hargather Schlieren image velocimetry (SIV) measures velocity fields by tracking the motion of naturally-occurring turbulent flow features in a compressible flow. Here the technique is applied to measuring the exhaust velocity profile of a liquid rocket engine. The SIV measurements presented include discussion of visibility of structures, image pre-processing for structure visibility, and ability to process resulting images using commercial particle image velocimetry (PIV) codes. The small-scale liquid bipropellant rocket engine operates on nitrous oxide and ethanol as propellants. Predictions of the exhaust velocity are obtained through NASA CEA calculations and simple compressible flow relationships, which are compared against the measured SIV profiles. Analysis of shear layer turbulence along the exhaust plume edge is also presented. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G25.00005: Direct numerical simulations of an arc-powered heater for used in a hypersonic wind tunnel PILBUM KIM, Marco Panesi, Jonathan Freund We study a model arc-heater using direct numerical simulations, in a configuration motivated by its used to generated inflow of a high-speed wind tunnel for hypersonics research. The flow is assumed to be in local thermal equilibrium (LTE) and is modeled with with 11 species (N$_2$ , O$_2$, NO, N, O, N$^+_2$ , O$^+_2$ , NO$^+$, N$^+$, O$^+$, $e^-$). The flow equations are solved in conjunction with an electrostatic field solver and the gas electric conductivity in LTE. The flow rate and the mean arc power are set to be $50.42\,$g/s and $84.7 \,$kW with $214.0\,$V of the mean arc voltage , respectively. We study the flow details, the heading and thrust mechanisms, and make general comparisons with a corresponding, though geometrically more complex, experimental configuration. We particularly interested in the radical species it produces and will potentially be present in the wind-tunnel test section. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G25.00006: Hotwire Probe Design and Calibration Technique for High Speed, High Temperature Flows Arman Mirhashemi, Joshua Szczudlak, Scott Morris This presentation will describe a hot-wire probe manufacturing and calibration technique for high speed flows with variable high temperatures. The hot-wire probe was designed to work in flow temperatures as high as 650 K. A new sensor wire welding process was developed to ensure the sustainability of hot-wire probe in high temperature, high speed flows. In order to account for the flow temperature variations, non-dimensional film cooling and temperature loading correction factors were utilized in the calibration equation introduced by Collis and Williams. These corrections factors are functions of the wire and flow temperatures. It is shown in this work, that by using the stagnation temperature in evaluating the correction factors and the flow properties, Mach number effects on the calibration curve were minimized. This method accounts for relatively large flow temperature changes and does not require multiple calibrations over a range of temperatures. The proposed method of correction was successfully applied in a flow with Mach number range of 0.01-0.5 and temperature range of 580-644 K. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G25.00007: Mach Number effects on turbulent superstructures in wall bounded flows Christian J. Kaehler, Matthew Bross, Sven Scharnowski Planer and three-dimensional flow field measurements along a flat plat boundary layer in the Trisonic Wind Tunnel Munich (TWM) are examined with the aim to characterize the scaling, spatial organization, and topology of large scale turbulent superstructures in compressible flow. This facility is ideal for this investigation as the ratio of boundary layer thickness to test section spanwise extent ratio is around 1/25, ensuring minimal sidewall and corner effects on turbulent structures in the center of the test section. A major difficulty in the experimental investigation of large scale features is the mutual size of the superstructures which can extend over many boundary layer thicknesses. Using multiple PIV systems, it was possible to capture the full spatial extent of large-scale structures over a range of Mach numbers from Ma = 0.3 - 3. To calculate the average large-scale structure length and spacing, the acquired vector fields were analyzed by statistical multi-point methods that show large scale structures with a correlation length of around 10 boundary layer thicknesses over the range of Mach numbers investigated. Furthermore, the average spacing between high and low momentum structures is on the order of a boundary layer thicknesses. [Preview Abstract] |
Monday, November 20, 2017 12:06PM - 12:19PM |
G25.00008: Integral Analysis of Boundary Layer Flows with Pressure Gradient Tie Wei, Yvan Maciel, Joseph Klewicki Boundary layer flows with pressure gradient is investigated using a novel similarity/integral analysis of the continuity equation and momentum equation in the streamwise direction. The analysis yields useful analytical relations for $V_e$, the mean wall-normal velocity at the edge of the boundary layer, and for the skin friction coefficient, $C_f$, in terms of the boundary layer parameters and in particular $\beta_{_{RC}}$, the Rotta-Clauser pressure gradient parameter. The analytical results are compared with experimental and numerical data and are found to be valid. One of the main findings is that for large positive $\beta_{_{RC}}$, the friction coefficient is closely related to $\beta_{_{RC}}$ as $C_f \propto 1/\beta_{_{RC}}$, because $\delta/\delta_1$, $\delta_1/\delta_2=H$ and $d\delta/dx$ become approximately constant. Here $\delta$ is the boundary layer thickness, $\delta_1$ is the displacement thickness, $\delta_2$ is the momentum thickness and $H$ is the shape factor. Another finding is that the mean wall-normal velocity at the edge of the boundary layer is related to other flow variables as $U_e V_e/u^2_\tau = H + (1+\delta/\delta_1+H)\beta_{_{RC}}$, where $U_e$ is the streamwise velocity at the edge of the boundary layer. [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G25.00009: Equation level matching: An extension of the method of matched asymptotic expansion for problems of wave propagation Luiz Faria, Rodolfo Rosales We introduce an alternative to the method of matched asymptotic expansions. In the "traditional" implementation, approximate solutions, valid in different (but overlapping) regions are matched by using "intermediate" variables. Here we propose to match at the level of the equations involved, via a "uniform expansion" whose equations enfold those of the approximations to be matched. This has the advantage that one does not need to explicitly solve the asymptotic equations to do the matching, which can be quite impossible for some problems. In addition, it allows matching to proceed in certain wave situations where the traditional approach fails because the time behaviors differ (e.g., one of the expansions does not include dissipation). On the other hand, this approach does not provide the fairly explicit approximations resulting from standard matching. In fact, this is not even its aim, which to produce the "simplest" set of equations that capture the behavior. [Preview Abstract] |
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