Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session BT: Experimental Techniques II |
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Chair: Rodney Bowersox, Texas A&M University Room: 204A |
Sunday, November 23, 2008 10:30AM - 10:43AM |
BT.00001: The accuracy of Reynolds shear stress and velocity-vorticity component correlations measured by a 12-sensor hot wire probe James Wallace, Petar Vukoslav\v{c}evi\'{c}, Elias Balaras, Nikolaos Beratlis A highly resolved (with sub-Kolmogorov length cells) turbulent channel flow DNS with $Re_\tau = 180$ was used to investigate the effects of spatial resolution and sensor arrangements of multi-sensor hot-wire probes on measurements of Reynolds shear stress and velocity-vorticity component correlations. Such correlations appear in the unclosed Reynolds shear stress gradient term in the mean momentum balance when expressed as $\partial \overline{uv}/\partial y = \overline{w \omega_y} - \overline{v \omega_z}$. The sensors are represented as points on the simulation grid, the effective velocity cooling each sensor is determined and the sensor cooling equations are then solved in response to the DNS field to obtain velocity and vorticity vector components. It is observed that the Reynolds shear stress and some of the velocity-vorticity correlations strongly depend, not only on the probe spatial resolution, but also on the arrangement of the sensors. There is no optimal sensor number and arrangement that gives the highest accuracy for all correlations. Various sensor numbers and arrangements are proposed depending on the correlations to be measured, and resolution effects for each of these arrangements are analyzed. [Preview Abstract] |
Sunday, November 23, 2008 10:43AM - 10:56AM |
BT.00002: A towed airborne platform for turbulence measurements over the ocean Carl Friehe, Djamal Khelif Measurements of wind stress and associated heat and mass fluxes (water vapor and CO2) down to $\sim $10 meters height over the ocean are required to establish parameterizations for wave, weather, hurricane and climate models. At high winds and accompanying sea states, such measurements are difficult or impossible. A new airborne instrumented towed platform has been developed that allows measurements down to 10 meters under radar-altitude control while the tow aircraft is safely above. Measurements include the three components of the wind, temperature, humidity, infrared surface temperature, CO2, and motion and navigational parameters. The bandwidth of the sensors allows calculation of the Reynolds averaged covariance's of stress and sensible heat and evaporation fluxes. Results are compared to equivalent measurements made with an instrumented aircraft. We would like to thank Robert Bluth of the Naval Postgraduate School and Jesse Barge and Dan Bierly of Zivko Aeronautics. [Preview Abstract] |
Sunday, November 23, 2008 10:56AM - 11:09AM |
BT.00003: Development of a Backlighted Color-coded Micro-DDPIV System and its Application to a Backward Facing Step Micro-channel Flow Wei-hsin Tien, Dana Dabiri, Morteza Gharib, Jay Hove A backlighted micro color-coded Defocusing Digital Particle Image Velocimetry (Micro-DDPIV) is the latest implementation of the backlighted color-coded DDPIV system introduced by Tien et al. (2008). This micro-DDPIV system utilizes the DDPIV technique with an infinity-corrected microscope lens system. The multi-element system performance and the refraction effects are corrected by a careful calibration process, and the optical distortion of the system is calibrated by using an image dewarping scheme. The technique is successfully applied to imaging a backward facing step micro-channel flow, and a three-dimensional velocity field is extracted. The image volume is 0.58mm$\times $0.58mm$\times $0.6mm. [Preview Abstract] |
Sunday, November 23, 2008 11:09AM - 11:22AM |
BT.00004: Background-oriented schlieren: Techniques and applications for multi-scale flow visualization and measurement Michael Hargather, Gary Settles Background oriented schlieren (BOS) is a new and versatile technique for imaging refractive fluid flows. This simplistic and low-cost flow visualization technique can be applied over a range of geometric scales, from typical laboratory setups to large outdoor experiments. The basic principles underlying BOS are briefly reviewed, including: background selection, sensitivity estimation, optimal geometric arrangement of optics, and analysis techniques. The influence of optical depth-of-field and geometric placement of the test specimen are also explored. Laboratory-scale applications and results include supersonic wind tunnel and candle-plume visualizations. The technique is also expanded to include ``natural-background-oriented schlieren,'' wherein naturally-occurring pseudo-random backgrounds such as trees and a cornfield are used to image outdoor explosions, gunshots, and thermal plumes. A wide range of potential backgrounds and applications is considered. [Preview Abstract] |
Sunday, November 23, 2008 11:22AM - 11:35AM |
BT.00005: Turbulence averaging techniques for IC engine unsteady flow using Laser Doppler Velocimetry Philip Schinetsky, Semih Olcmen, Mebougna Drabo, Marcus Ashford Turbulence in unsteady flow fields is complex in nature not only because of the cycle-to-cycle variations of the turbulence but also the time dependent mean velocity. Defining and quantifying turbulence in unsteady flow fields is important since the level of turbulence applies directly to processes such as the mixing of gasoline and air in internal combustion engines. This same analysis method can also be used in fields where unsteady time-dependent data is obtained. In this study one component LDV velocity measurements made in an off the shelf IC engine were used to study unsteady turbulence. Phase and cyclic averaging techniques, along with wavelet transform analysis techniques were used to determine the unsteady turbulence levels. In addition, these techniques were applied to a predetermined sinusoidal signal with a known turbulence level to choose the best method to identify turbulence in unsteady flows. [Preview Abstract] |
Sunday, November 23, 2008 11:35AM - 11:48AM |
BT.00006: Development of a High-Speed Three-Dimensional Flow Visualization Technique Brian Thurow, Kyle Lynch A high-speed 3-D flow visualization technique has been developed for the investigation of turbulent flows. The technique is based on the scanning of a laser light sheet through the flow field. High-speeds are possible using a recently developed MHz rate pulse burst laser system, an ultra-high-speed camera capable of 500,000 fps and a galvanometric scanning mirror. The current technique is capable of producing 3-D images with 220 x 220 x 68 resolution and exposure times of 136 microseconds. Exposure times on the order of 10s of microseconds are possible using higher framing rate cameras. The technique is demonstrated by visualizing the vortex dominated flow of a round turbulent jet where the presence of ring vortices and 3-D azimuthal instabilities is clearly illustrated. [Preview Abstract] |
Sunday, November 23, 2008 11:48AM - 12:01PM |
BT.00007: Manipulating the anisotropy of turbulence Kelken Chang, Gregory Bewley, Eberhard Bodenschatz We obtain two-point velocity statistics in a turbulent flow as the flow is subject to a systematic variation from isotropy. We explore values of the ratio of axial to radial root-mean-square velocity fluctuations between 0.5 and 2.0, while maintaining cylindrical symmetry. We measure the Eulerian transverse spatial correlation function and the second order Eulerian transverse structure function at Reynolds numbers up to 500, based on the Taylor microscale, and observe changes of the integral length scales and Taylor microscales as the flow deviates from isotropy. Additionally, the energy dissipation rates for both the isotropic and anisotropic flows are estimated from the second order Eulerian transverse structure functions and the changes of these rates subject to the variation from isotropy are reported. [Preview Abstract] |
Sunday, November 23, 2008 12:01PM - 12:14PM |
BT.00008: Volumetric Three Dimensional Flow Measurements Rajan Menon, Dan Troolin, Wing Lai Most flows, generally being three-dimensional in nature, need diagnostic techniques that provide instantaneous vector fields and detailed statistical properties in a true 3-dimensional region -- a cube. Till now, the diagnostics capabilities have been limited to measuring the instantaneous velocity vectors at a point, in a plane or a thin layer. Starting with a patented approach, a new multi-aperture imaging approach has been incorporated into a system that captures the vector field in a volume. Triple-port imaging approach combined with triplet matching correlation technique is used to extract the velocity of particles, from images, in a cubic measuring region. This approach also enables the system to have, for the first time in particle image velocimetry, an integrated imaging system that does not need any focusing or aperture adjustment. A pulsed volume illumination system combined with the HYPERSTREAMING system for continuous image capture and transfer to the computer is used to get temporal and spatial development of three dimensional flows. System details along with measurements carried out in a wide range of flows presented in the paper clearly show the diagnostics potential of this true 3D system to explore the details of wake flows, vortex dynamics, mixing and other complex flows. [Preview Abstract] |
Sunday, November 23, 2008 12:14PM - 12:27PM |
BT.00009: Temperature-Cancelled Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Pressure Field Measurement Takuma Kuriki, Takeshi Miyazaki, Hirotaka Sakaue A new temperature-cancellation method for pressure-sensitive paint (PSP) technique is introduced. This uses an intermediate range of two luminescent peaks which have opposite temperature dependencies. This method gives an advantage from a conventional two-color method especially in unsteady pressure field measurements by using a single band-pass filter. The present method is applied to anodized-aluminum pressure-sensitive paint (AA-PSP), which is known as one of the fastest PSPs. Peak control study as well as temperature- and pressure-calibrations is included. The dipping deposition parameters, such as the luminophore concentration and the dipping duration, are related to the peak control. A peak-controlled AA-PSP shows temperature cancellation in the calibrated temperature range (10 to 50 $^{\circ}$C). Pressure sensitivity is 0.4, which is comparable to that of conventional AA-PSP. The present temperature-cancellation method will be demonstrated in unsteady pressure field of an impinging jet in the final version. [Preview Abstract] |
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