Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M29: Experimental Techniques: General |
Hide Abstracts |
Chair: Jun Chen, Purdue University Room: 2014 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M29.00001: Customized turbulent flow fields generated by means of an active grid Michael Hoelling, Nico Reinke, Joachim Peinke Wind tunnel experiments, which should clarify the interaction of wind energy converters and the ambient turbulent field, should be performed under realistic flow conditions. For the generation of realistic turbulent flow conditions we use an active grid. This grid allows for the generation of flows with high turbulence intensity and even to repeat those turbulent fields to a certain degree. Moreover, flow features are to a certain extent tuneable, e.g. velocity increments distributions or energy density spectrum, realized by individually controllable horizontal and vertical rotating axes, which are equipped with flaps. The rotation patterns of the axes over time are defined in an excitation protocol. The challenge is designing an excitation protocol, which generates a flow flied for a specific application. A general approach is still missing. Our approach allows estimating the flow features to given excitation protocols. The approach is based on the assumption that the flow field behind an active grid consists basically of different turbulent pulses, which belong to the excitation setting. Our approach gives a sequence of those pulses, which we call synthetic velocity time series, which is made on a computer. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M29.00002: Measurements of the aerodynamic characteristics of the turbo-jav Kenta Yamamoto, Tomoya Nakajima, Tomoaki Itano, Masako Sugihara-Seki The ``turbo-jav'' which is used for the javelic throw in the junior Olympic games has four tail fins. In order to investigate the aerodynamic characteristics of the turbo-jav with an emphasis on the effect of the fins, we performed wind tunnel tests, throwing experiments and numerical simulations of the flight for intact turbo-javs as well as turbo-javs with their fins cut. The wind tunnel tests showed that the drag and lift coefficients for the intact turbo-javs are larger than the corresponding values for the turbo-javs without fins. As the angle of attack increases from 0, the pitching moments for the intact turbo-javs decrease from 0, whereas the moments for the turbo-javs without fins increase. In accord with this property, the throwing experiments showed that intact turbo-javs fly stably with oscillating angle of attack around 0. The flight distance, the orbit and the variation of angle of attack for the intact turbo-javs launched by a launcher agree closely with the numerical simulation performed based on the wind tunnel tests. A comparison of throwing experiments by students and by the launcher suggested significant effects of the rolling motion of the turbo-jav on its flight characteristics. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M29.00003: On the measurement of turbulence with unmanned aerial vehicles Brandon Witte, Michael Thamann, Sean Bailey We address the challenge of taking the novel approach of using highly instrumented and autonomous unmanned aerial vehicles (UAVs) to spatially interrogate the atmospheric boundary layer's turbulent flow structure over a wide range of length scales. This approach will introduce new capabilities not available in contemporary micro-meteorological measurement techniques: the ability to spatially sample the flow field over a wide range of spatial scales; a reduced reliance on assumptions regarding the temporal evolution of the turbulence; the ability to measure in a wide range of boundary conditions and distance from the earth's surface; the ability to gather many boundary layer thicknesses of data during brief periods of statistical quasi-stationarity; and the ability to acquire data where and when it is needed. We describe recent progress made in developing purpose-built airframes, integrating sensors into those airframes, and developing data analysis techniques to isolate the atmospheric turbulence from the measured velocity signal. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M29.00004: Measurement of wall shear stress in a pulsatile pipe flow system using micro-pillar shear sensor (MPS3) Vrishank Raghav, Christine Garcia, Ebenezer Gnanamanickam, Ajit Yoganathan The measurement of unsteady wall shear stress (WSS) in a pulsatile flow system is quite a challenge in experimental fluid mechanics. Recent developments in micro fabrication techniques have resulted in a novel measurement technique called the micro-pillar shear stress sensor (MPS3). It is a micro-pillar mounted on the surface of interest, which deflects an amount proportional to the shear stress it experiences. This technique has been widely used, validated and applied to measure turbulent WSS in several flow configurations. In this work, the MPS3 technique is used to measure WSS for a pulsatile fully developed pipe flow. The main objective here is to validate this technique for pulsatile pipe flow applications. For this purpose the WSS measurements obtained are compared with those obtained from analytical womersley solutions of the pulsatile flow system in the laminar flow regime. Statistical metrics will be used to better understand the measured WSS through the time period of the pulsatile flow. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M29.00005: Further development of a wall-shear-stress sensor and validation in laminar and turbulent flows Laurent Mydlarski, Pierre-Alain Gubian, James Medvescek, Cristian Tomazela Prado, B. Rabi Baliga The present work involves the further development of a wall-shear-stress sensor, and its subsequent validation in both laminar and turbulent flows. Inspired by the works of Spazzini \emph{et al.}, \emph{Meas. Sci. Technol.}, 1999 and Sturzebecher \emph{et al.}, \emph{Exp. Fluids}, 2001, the sensor consists of a tungsten hot-wire flush-mounted over a shallow rectangular slot, which serves to reduce heat loss to the substrate and therefore improve the frequency response of the sensor -- a problem that frequently plagues hot-film wall-shear-stress sensors in many applications in air. Different aspects of the design, construction, operation and validation of the sensor will be presented. Particular attention will be paid to the performance of the sensor in fully developed turbulent channel flow, where measurements of statistical moments, probability density functions, and spectra of the wall-shear stress will be considered for turbulent Reynolds numbers (based on the friction velocity and half-height, $Re_\tau$) in the range $200 \le Re_{\tau} \le 900$. These measures will be compared with previous (experimental and numerical) work studying the wall-shear stress. The evolution of the statistics with $Re_\tau$ will also be discussed. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M29.00006: Design of a High-Reynolds Number Recirculating Water Tunnel Libin Daniel, Brian Elbing An experimental fluid mechanics laboratory focused on turbulent boundary layers, drag reduction techniques, multiphase flows and fluid-structure interactions has recently been established at Oklahoma State University. This laboratory has three primary components; (1) a recirculating water tunnel, (2) a multiphase pipe flow loop, and (3) a multi-scale flow visualization system. The design of the water tunnel is the focus of this talk. The criteria used for the water tunnel design was that it had to produce a momentum-thickness based Reynolds number in excess of 10$^{\mathrm{4}}$, negligible flow acceleration due to boundary layer growth, maximize optical access for use of the flow visualization system, and minimize inlet flow non-uniformity. This Reynolds number was targeted to bridge the gap between typical university/commercial water tunnels (10$^{\mathrm{3}})$ and the world's largest water tunnel facilities (10$^{\mathrm{5}})$. These objectives were achieved with a 152 mm (6-inch) square test section that is 1 m long and has a maximum flow speed of 10 m/s. The flow non-uniformity was mitigated with the use of a tandem honeycomb configuration, a settling chamber and an 8.5:1 contraction. The design process that produced this final design will be presented along with its current status. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M29.00007: A new technique to linearly stratify a fluid Mickael Bosco, Patrice Meunier Given that oceans and the atmosphere are stratified, most environmental flows like island and mountain range wakes are strongly influenced by the mean density gradient. Consequently, a great number of laboratory experiments have been run using stratified fluids to study geophysical flow. The double-bucket method is generally used to create a stable linearly stratified fluid. The water from the first bucket filled with salted water is slowly deposited at the surface of the tank with a floater and the density of the first bucket is gradually decreased by the addition of fresh water from a second bucket. Nevertheless, this method is not very convenient for large tank as the two buckets are very large and can easily be bulky. A simple method has been created which only needs two walls inside the tank. One plain barrier will ensure watertightness between the two sides of the tank and one holey barrier will allow density-driven exchanges at the origin of a stable linear stratification. One of the motivations was to analyze a stratified cylinder wake. The study has revealed four 3D unstable modes that appears behind the cylinder. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M29.00008: Surrogate Immiscible Liquid Solution Pairs with Refractive Indexes Matchable Over a Wide Range of Density and Viscosity Ratios Rajat Saksena, Kenneth T. Christensen, Arne J. Pearlstein Use of laser diagnostics in liquid-liquid flows is limited by refractive index mismatch. This can be avoided using a surrogate pair of immiscible index-matched liquids, with density and viscosity ratios matching those of the original liquid pair. We demonstrate that a wide range of density and viscosity ratios is accessible using aqueous solutions of 1,2-propanediol and CsBr (for which index, density, and viscosity are available), and solutions of light and heavy silicone oils and 1-bromooctane (for which we measured the same properties at 119 compositions). For each liquid phase, polynomials in the composition variables were fitted to index and density and to the logarithm of kinematic viscosity, and the fits were used to determine accessible density and viscosity ratios for each matchable index. Index-matched solution pairs can be prepared with density and viscosity ratios equal to those for water-liquid CO$_{\mathrm{2}}$ at 0$^{\mathrm{o}}$C over a range of pressure, and for water-crude oil and water-trichloroethylene, each over a range of temperature. For representative index-matched solutions, equilibration changes index, density, and viscosity only slightly, and chemical analysis show that no component of either solution has significant interphase solubility. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M29.00009: Dynamic mode decomposition analysis of instability of the flow past rotating sphere Maciej Skarysz, Sophie Goujon-Durand, Jose Eduardo Wesfreid Dynamic mode decomposition (DMD) is an effective method to obtain the description of coherent features of fluid flow generated both by numerical simulations and experimental measurements. Extraction of dynamic modes connected with the frequency created by the method provide essential information and made our understanding of fluid-dynamical process more meaningful. The wake behind rotating sphere for low Reynolds number (lower than 400) was experimentally investigated. Different regimes depending both on rotating rate and Reynolds number appears and was characterized by different multiple frequencies observed in the wake. In this case the DMD analysis was very efficient to expose full spectra and new modes remaining undetectable for other methods. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M29.00010: Real-time contaminant sensing and control in civil infrastructure systems Sara Rimer, Nikolaos Katopodes A laboratory-scale prototype has been designed and implemented to test the feasibility of real-time contaminant sensing and control in civil infrastructure systems. A blower wind tunnel is the basis of the prototype design, with propylene glycol smoke as the ``contaminant.'' A camera sensor and compressed-air vacuum nozzle system is set up at the test section portion of the prototype to visually sense and then control the contaminant; a real-time controller is programmed to read in data from the camera sensor and administer pressure to regulators controlling the compressed air operating the vacuum nozzles. A computational fluid dynamics model is being integrated in with this prototype to inform the correct pressure to supply to the regulators in order to optimally control the contaminant's removal from the prototype. The performance of the prototype has been evaluated against the computational fluid dynamics model and is discussed in this presentation. Furthermore, the initial performance of the sensor-control system implemented in the test section of the prototype is discussed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700