Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HH: Experimental Techniques: Thermal Anemometry |
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Chair: Charles Petty, Michigan State University Room: Hilton Chicago Williford B |
Monday, November 21, 2005 1:20PM - 1:33PM |
HH.00001: Development of NSTAP: Nanoscale Thermal Anemometry Probe Gary Kunkel, Alexander Smits, Craig Arnold The current development of NSTAP, a nanoscale thermal anemometry probe funded by the National Science Foundation CTS-0421147, will be presented. Standard semiconductor processing techniques, focused ion beam milling, and precision laser micromachining are used to manufacture free standing platinum wires on current carrying aerodynamic supports. The main purpose of this probe is to use it in the high-pressure, high-Reynolds-number test facilities at Princeton University and therefore the ultimate goal is to decrease the length of the sensing wire to less than \mbox{10 $\mu$m}. Preliminary results on \mbox{$0.3\times0.3\times60$ $\mu$m} wires are promising and fluctuating responses to turbulent flow are similar to those from conventional wires. The challenges of development and electronic characterization of the probe also will be discussed. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HH.00002: A Double X-Array Hot-wire Probe for Simultaneous Three-Component Velocity Measurements Douglas Neal, John Foss, St\'{e}phane Moreau Four hot-wire sensors, mounted in a double X-array on a common probe shaft, can be used to obtain simultaneous values for three velocity components. Important turbulence quantities, such as the full Reynolds stress tensor, readily follow. The complexities of this probe along with the calibration and velocity component extractions from the four time series will be presented. Comparisons with other existing 3+ wire probes\footnote{ Wallace, J.M. and Foss, J.F., 1995, ``The Measurement of Vorticity in Turbulent Flows'', \textit{Ann. Rev. Fluid Mech.}, 27, p. 469-514} will be discussed. Representative turbulence data collected using the double x-wire probe are presented for a low Mach number rotor-stator configuration. These phase-averaged measurements were collected directly downstream of the stator and provide important information about the design of these devices, along with insight into their complex flow field. The implications of these measurements to on-going CFD modeling efforts will be referenced. [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HH.00003: Control of the dynamic non-linearity in a Constant Voltage Anemometer Genevi\`{e}ve Comte-Bellot , Julien Weiss, Jean-Christophe Bera A second harmonic appears in most hot-wire anemometers due to a combined effect of the large amplitudes of the turbulent fluctuations, the thermal lag of the wire, and the electronic circuitry - see Corrsin Handbook of Physics, \underline {8}, 524-590, 1963, for a constant current anemometer (CCA) and Freymuth, Rev. Sci Instrum, \underline {40}, 258-262, 1969, for a constant temperature anemometer (CTA). For a constant voltage anemometer (CVA), which is a recent and innovative technique, it is shown that the second and higher harmonics can be rejected by inverting the differential equation which expresses the wire response and which is known (Comte-Bellot, CRC Handbook, 1998). This treatment is made when post-processing the data and it does not slow down the experiments. The constant frequency bandwidth insured by the partial thermal lag correction available in a CVA is also preserved. It is shown that the skewness factors of turbulent fluctuations, which are affected by the presence of a second harmonic, retrieve correct values. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HH.00004: The dependence of Nusselt number on Reynolds number for a hot-wire sensor in supercritical CO$_{2}$ flow Petar Vukoslavcevic, James Wallace An analysis of the heat transfer mechanism around a hot-wire sensor in superctitical CO$_{2}$ flow has been performed, and the dependence of the Nusselt number (N$_{u})$ on the Reynolds number (R$_{e})$ has been determined. A special, closed flow loop, capable of inducing variable speed flow at different pressures and temperatures in the ranges of 0.15-2 m/s, 15-70$^{\circ}$C and 1-100 bar, has been used to create a supercritical CO$_{2}$ flow around a hot-wire sensor operated in the constant temperature mode. The N$_{u}$ and R$_{e}$ numbers were determined based on the known heat convected from the sensor, the flow speed and the sensor temperature and dimensions. The experiment was performed along a line of constant 80 bar pressure in the temperature range of 25-65$^{\circ}$C. It was found that, at a given pressure and temperature, the relation N$_{u}$=F(R$_{e})$ has the classical form N$_{u}$=M+NR$_{e}^{n}$, with the parameters M and N being functions of pressure and temperature. The dependence of these parameters on temperature was analyzed, and the most convenient reference temperature was chosen. In contrast to the operation of hot-wires in air and water, the dependence of the parameters M and N on the Prandtl number can result in nonunique solutions. [Preview Abstract] |
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