Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L32: Experiments: General Methods |
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Chair: Xiaofeng Liu, San Diego State University Room: 313 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L32.00001: Rotating parallel ray omni-directional integration for instantaneous pressure reconstruction from measured pressure gradient Xiaofeng Liu, Seth Siddle-Mitchell This paper presents a novel pressure reconstruction method featuring rotating parallel ray omni-directional integration, as an improvement over the circular virtual boundary integration method introduced by Liu and Katz (2003, 2006, 2008 and 2013) for non-intrusive instantaneous pressure measurement in incompressible flow field. Unlike the virtual boundary omni-directional integration, where the integration path is originated from a virtual circular boundary at a finite distance from the real boundary of the integration domain, the new method utilizes parallel rays, which can be viewed as being originated from a distance of infinity, as guidance for integration paths. By rotating the parallel rays, omni-directional paths with equal weights coming from all directions toward the point of interest at any location within the computation domain will be generated. In this way, the location dependence of the integration weight inherent in the old algorithm will be eliminated. By implementing this new algorithm, the accuracy of the reconstructed pressure for a synthetic rotational flow in terms of r.m.s. error from theoretical values is reduced from 1.03{\%} to 0.30{\%}. Improvement is further demonstrated from the comparison of the reconstructed pressure with that from the Johns Hopkins University isotropic turbulence database (JHTDB). [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L32.00002: Wire-cooling based synthetic experiment to evaluate multi-sensor hotwire performance Spencer Zimmerman, Caleb Morrill-Winter, Joseph Klewicki Representation of the Navier-Stokes equations in vorticity form elucidates the importance of vorticity in transporting momentum in turbulent flows. While hotwire sensors have been previously employed to measure multiple components of velocity and vorticity simultaneously, physical limitations inhibit the resolution of ever-smaller dynamically relevant motions, and thus cap the range of measurable Reynolds numbers in a given facility. Cross-stream velocity measurement arrays are also susceptible to error caused by non-uniform flow between array elements. The goal is therefore to minimize the sensing area of the probe while maintaining a wire orientation that will effectively recover the desired signals. We present a wire arrangement aimed at measuring all three components of vorticity about a common point. The turbulent boundary layer DNS of Sillero (\textit{Phys. Fluids} \textbf{25}, 2013) is utilized to generate synthetic results from the proposed orientation. Effective cooling velocities are calculated at interrogation nodes corresponding to wire locations. Subsequent recovery of velocity components from cooling velocities incorporates inter-array gradient error into the results. The sensor geometries that best reproduce the known vorticity signals are described and discussed. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L32.00003: Large Field of View PIV Measurements of Air Entrainment by SLS SMAT Water Sound Suppression System Matthew Stegmeir, Stamatios Pothos, Dan Bissell Water-based sound suppressions systems have been used to reduce the acoustic impact of space vehicle launches. Water flows at a high rate during launch in order to suppress Engine Generated Acoustics and other potentially damaging sources of noise. For the Space Shuttle, peak flow rates exceeded 900,000 gallons per minute. Such large water flow rates have the potential to induce substantial entrainment of the surrounding air, affecting the launch conditions and generating airflow around the launch vehicle. Validation testing is necessary to quantify this impact for future space launch systems. In this study, PIV measurements were performed to map the flow field above the SMAT sub-scale launch vehicle scaled launch stand. Air entrainment effects generated by a water-based sound suppression system were studied. Mean and fluctuating fluid velocities were mapped up to 1m above the test stand deck and compared to simulation results. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L32.00004: The effect of freestream turbulence on the wake of a 2D square prism Daniel Lander, Chris Letchford, Michael Amitay, Gregory Kopp The effect of freestream turbulence (FST) on a $2D$ square prism is investigated at $Re_D=5.0\times10^4$ using long duration Time Resolved Particle Image Velocimetry (TR-PIV). Increasing the FST results in alterations to the flow field in the shear-layer and base regions and the origins of the apparent differences are discussed. The triple decomposition technique is employed to disintegrate changes attributable to the coherent and random components of the global wake stresses. In the presence of FST the vortex formation process is altered due to an increase reattachment time of the separating shear-layers on the trailing edge of the prism. This is accompanied by a transposition of the von-K\'{a}rm\'{a}n vorticies observed in the phase averaged flow field; a feature complementary to the narrowing and lengthening of the steady wake commonly observed in the literature. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L32.00005: The 2d-LCA as an alternative to x-wires Jaroslaw Puczylowski, Michael H\"olling, Joachim Peinke The 2d-Laser Cantilever Anemometer (2d-LCA) is an innovative sensor for two-dimensional velocity measurements in fluids. It uses a micostructured cantilever made of silicon and SU-8 as a sensing element and is capable of performing mesurements with extremly high temporal resolutions up to 150kHz. The size of the cantilever defines its spatial resolution, which is in the order of 150 $\mu$m only. Another big feature is a large angular range of 180$^{\circ}$ in total. The 2d-LCA has been developed as an alternative measurement method to x-wires with the motivation to create a sensor that can operate in areas where the use of hot-wire anemometry is difficult. These areas include measurements in liquids and in near-wall or particle-laden flows. Unlike hot-wires, the resolution power of the 2d-LCA does not decrease with increasing flow velocity, making it particularly suitable for measurements in high speed flows. Comparative measurements with the 2d-LCA and hot-wires have been carried out in order to assess the performance of the new anemometer. The data of both measurement techniques were analyzed using the same stochastic methods including a spectral analysis as well as an inspection of increment statistics and structure functions. Furthermore, key parameters, such as mean values of both velocity components, angles of attack and the characteristic length scales were determined from both data sets. The analysis reveals a great agreement between both anemometers and thus confirms the new approach. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L32.00006: Accidental Turbulent Discharge Rate Estimation from Videos Eric Ibarra, Franklin Shaffer, \"Omer Sava\c{s} A technique to estimate the volumetric discharge rate in accidental oil releases using high speed video streams is described. The essence of the method is similar to PIV processing, however the cross correlation is carried out on the visible features of the efflux, which are usually turbulent, opaque and immiscible. The key step in the process is to perform a pixelwise time filtering on the video stream, in which the parameters are commensurate with the scales of the large eddies. The velocity field extracted from the shell of visible features is then used to construct an approximate velocity profile within the discharge. The technique has been tested on laboratory experiments using both water and oil jets at $Re \approx 10^5$. The technique is accurate to 20\%, which is sufficient for initial responders to deploy adequate resources for containment. The software package requires minimal user input and is intended for deployment on an ROV in the field. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L32.00007: Thermal conductivity measurements using hot-wires at small Peclet number Gilad Arwatz, Yuyang Fan, Marcus Hultmark The feasibility of using hot-wires to measure gas thermal conductivity is investigated. When the local Peclet number of a hot-wire is small (Pe\textless \textless 1), molecular diffusion dominates the heat transport, and the wire becomes less sensitive to velocity. This phenomenon can be utilized to measure the thermal conductivity of the gas. To investigate the viability of the principle of operation, a lumped capacitance model is proposed, capturing the effects of both convection and conduction on heat transfer from the wire. By investigating the sensitivity of the model to velocity, temperature and conduction, it is shown that as wire dimension decreases, the sensor becomes less sensitive to both velocity and temperature and more sensitive to conduction. The model also captures the effect of varying wire dimension as well as overheat ratio. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L32.00008: Toward the measurement of differentiable high resolution profile data in wall turbulence John Elsnab, Jason Monty, Christopher White, Manoochehr Koochesfahani, Joseph Klewicki High resolution streamwise velocity profiles are obtained in fully developed channel flow using molecular tagging velocimetry (MTV) over a Reynolds number based upon friction velocity and channel half-height from 200 to 2000. Due to the spatial resolution afforded from the MTV technique (800 points per profile), the velocity profile is differentiable in the wall-normal direction. This, along with pressure drop measurements, allows estimates of the mean viscous force and Reynolds stress (RS) via manipulation of the mean momentum equation. Differentiation of the RS profile allows for an investigation into the gradient of the RS. This quantity is central to the dynamics, as it acts as a net source or sink of mean momentum depending upon position relative to the RS maximum. The MTV technique and methods used to obtain the profiles are discussed. The main issue with obtaining smooth profiles is dealing with the inherent spatial pattern in the array of an intensified CCD camera. This pattern is significant in the outer region, where the profile variations and the data spacing relative to the inherent scales of motion are small. A dynamic flat-field image is used to remove a majority of this pattern. The MTV results are compared and evaluated relative DNS data. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L32.00009: Optical Properties of Inductively RF Discharge for Argon (Ar) Murat Tanisli, Neslihan Sahin, Sercan Mertadam Different power supplies in laboratories can produce plasma, which is the fourth state of matter. In this study, the inductively radio frequency (RF) plasma of Ar at low pressure in the quartz glass reactor prepared for special design is obtained. Discharge properties of the generated plasma are examined with optical emission spectroscopy (OES). For RF power values, Ar was sent in certain periods and amounts to reactor in which were obtained the low pressure with vacuum pump. Plasma was generated and the data obtained from OES were composed for calculating of electron temperature. In this way, the electron transitions can also be investigated from data. In the presence of experimental data, the collisional radiative model can be used to obtain of the electron temperature. In addition, the various graphs of the plasma parameters are showed. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L32.00010: Transient laminar opposing mixed convection in a symmetrically heated duct with a plane symmetric sudden contraction-expansion: Buoyancy an inclination effects Lorenzo Mart\'Inez-Su\'astegui, Enrique Barreto, C\'esar Trevi\~no Transient laminar opposing mixed convection is studied experimentally in an open vertical rectangular channel with two discrete protruded heat sources subjected to uniform heat flux simulating electronic components. Experiments are performed for a Reynolds number of Re $=$ 700, Prandtl number of Pr $=$ 7, inclination angles with respect to the horizontal of $\gamma \quad =$ 0$^{\mathrm{o}}$, 45$^{\mathrm{o}}$ and 90$^{\mathrm{o}}$, and different values of buoyancy strength or modified Richardson number, Ri* $=$ Gr*/Re$^{\mathrm{2}}$. From the experimental measurements, the space averaged surface temperatures, overall Nusselt number of each simulated electronic chip, phase-space plots of the self-oscillatory system, characteristic times of temperature oscillations and spectral distribution of the fluctuating energy have been obtained. Results show that when a threshold in the buoyancy parameter is reached, strong three-dimensional secondary flow oscillations develop in the axial and spanwise directions. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L32.00011: A Discretized Method for Deriving Vortex Impulse from Volumetric Datasets Noam Buckman, Leah Mendelson, Alexandra Techet Many biological and mechanical systems transfer momentum through a fluid by creating vortical structures. To study this mechanism, we derive a method for extracting impulse and its time derivative from flow fields observed in experiments and simulations. We begin by discretizing a thin-cored vortex filament, and extend the model to account for finite vortex core thickness and asymmetric distributions of vorticity. By solely using velocity fields to extract vortex cores and calculate circulation, this method is applicable to 3D PIV datasets, even with low spatial resolution flow fields and measurement noise. To assess the performance of this analysis method, we simulate vortex rings and arbitrary vortex structures using OpenFOAM computational fluid dynamics software and analyze the wake momentum using this model in order to validate this method. We further examine a piston-vortex experiment, using 3D synthetic particle image velocimetry (SAPIV) to capture velocity fields. Strengths, limitations, and improvements to the framework are discussed. [Preview Abstract] |
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