Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session KI: Experimental Techniques IV |
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Chair: Dana Dabiri, University of Washington Room: Salt Palace Convention Center 250 C |
Tuesday, November 20, 2007 8:00AM - 8:13AM |
KI.00001: A.C. Plasma Anemometer for Axial Compressor Stall Warning Eric Matlis, Joshua Cameron, Scott Morris, Thomas Corke Compressor sections of turbo jet engines are subject to stall and surge as a result of flow instabilities that occur upstream of the compressor rotor. One of the instability modes that contributes to compressor surge is the so-called `spike' mode of stall inception. It has been shown that this mode of instability can be predicted before onset by performing real-time statistical auto-correlation measurements of the blade-passing pressure characteristic at the mid-chord location of the rotor. These measurements are performed with pressure sensors or hot-wires that are too fragile for a full-scale compressor. We have developed a sensor that can survive the vibration and temperatures of a full-scale rig while providing the bandwidth necessary to resolve the blade passage signature required by this coherence technique. This sensor, called the Plasma Anemometer, provides high-bandwith point measurements of velocity or pressure fluctuations with unparalleled mechanical robustness and resistance to vibration and thermal effects. [Preview Abstract] |
Tuesday, November 20, 2007 8:13AM - 8:26AM |
KI.00002: Development of a Touch Mode Pressure Transducer using Electroactive Polymers (EAP) Philippe Lavoie, Florence Rosenblatt, Lorenzo Iannucci, Jonathan F. Morrison Accurate measurements of pressure fluctuations at small temporal, O(1) kHz, and ``meso'' spatial scales, O(10-100) $\mu $m, are of critical importance in a number of applications such as the study and control of turbulent boundary layers at high Reynolds numbers and quantification of vorticity in super-fluids. While MEMS technology is enabling important advances in the performance of miniaturized pressure sensors, the challenge posed by the diminishing sensitivity with decreasing sensor size remains an important issue. Preliminary work on the development of a novel transducer design is presented. It takes advantage of both the increased sensitivity associated with a capacitance-based sensor operating in touch mode and the properties of EAP which have not hitherto been used for this application. EAP have high electromechanical efficiency, are capable of very large strains and can also be operated so that the diaphragm is operating as a constant displacement device. Results from a macro-scale, proof-of-concept prototype are compared to a finite element analysis (FEA) model. The FEA model, which uses an electro-mechanical coupling to represent the behavior of the EAP membrane, is used to optimize the design and predict transducer sensitivity at the meso-scale. [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:39AM |
KI.00003: Measurement of Dynamic Wall-Shear Stress using the Micro-Pillar Sensor MPS$^3$ Sebastian Gro\ss e, Wolfgang Schr\"oder The micro-pillar shear stress sensor MPS$^3$ will be presented. The sensor is based on flexible cylinders that protrude into the viscous sublayer. The sensor concept allows the easy assessment of the two-dimensional wall-shear stress distribution in turbulent flows with a spatial resolution of approximately five viscous units. Both, the streamwise and spanwise wall-shear stress components can be detected simultaneously. The sensor response is detected optically and depending on the optical resolution the system allows to determine the wall-shear stress within $3\%$ accuracy. The static sensor calibration in linear shear flow will be presented and an analytical estimate of the pillar dynamic response will be compared to experimental calibration results. Depending on the sensor structure, turbulent fluctuations up to $1000-2000~Hz$ can be detected. Measurements of the mean and fluctuating wall-shear stress in fully developed turbulent pipe flow at Reynolds number~$Re_b$ based on the bulk velocity $U_b$ and the pipe diameter $D$ ranging from $Re_b=5000-20000$ were performed. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. First results of the dynamic wall-shear stress will be discussed and compared to results from the literature. [Preview Abstract] |
Tuesday, November 20, 2007 8:39AM - 8:52AM |
KI.00004: Turbine Blade Aero-elastic Mode Estimates from Blade Image Velocimetry Thomas Apker, Mikrut Paul, Scott Morris, Thomas Corke Blade Image Velocimetry (BIV) is a method of using a Particle Image Velocimetry (PIV) laser and optics to observe the motion of the unsupported end (tip) of a finite-length turbine blade in a rotating stage of a gas turbine that is undergoing linear aeroelastic deformation. The objective is to infer the combination of bending modes of the blade based on the tip motion. The projection from the tip motion to the full blade motion is made by calculating the eigenmodes of the simply supported geometry, and the inverse of their projection onto the tip space. From this, an individual BIV image can be used to estimate the instantaneous motion of the beam. A sequence of images can be used to estimate relative modal amplitudes. The steps to achieve this will be presented. Validation will come by comparing estimates made by the BIV method with direct measurements of the full motion of a self excited turbine blade obtained using a laser vibrometer. [Preview Abstract] |
Tuesday, November 20, 2007 8:52AM - 9:05AM |
KI.00005: Development of Pressure Sensitive MicroBeads for the Simultaneous Measurements of Pressure and Velocity Fletcher Kimura, Miguel Rodriguez, Jesse McCann, Dana Dabiri, Gamal Khalil, James Callis, Younan Xia, Martin Gouterman, Brenden Carlson We have recently synthesized pressure sensitive microbeads (PSBeads) consisting of a platinum octaethylporphryin luminophore in a polystyrene matrix, and a novel osmium-based luminophore in a silicon dioxide matrix. Since these PSBeads are to provide simultaneous measurements of pressure and velocity in turbulent and/or high speed flows, their response times must be sufficiently fast. A shock tube was constructed to provide a test facility where the response time of the microspheres could be reliably measured. Initial studies showed response times are on the order of 20 $\mu $s -- 2 ms when exposed to shock strengths of $\sim $1.07 $M$ ($\Delta P \quad \approx $ 10-12 kPa). We further use this facility to obtain preliminary simultaneous pressure and velocity measurements before and after a shock wave. [Preview Abstract] |
Tuesday, November 20, 2007 9:05AM - 9:18AM |
KI.00006: The Use of Magneto-hydrodynamic Convection for the Determination of Mercury (II) Ions in Aqueous Solutions Yogendra M. Panta, Shizhi Qian, Marcos A. Cheney We experimentally investigated the effects of magnetic fields on the anodic currents in the determination of mercury (II) ions in aqueous solutions with the linear sweep stripping voltammetry technique. In the stripping analysis, a potential difference is applied across the working and reference electrodes positioned in the working sample, then a transmitted current density through the sample results. When the electrochemical cell is placed on a permanent magnet, a magneto-hydrodynamic (MHD) convection is induced through the interaction between the current density and the magnetic field. The induced MHD convection enhances the ionic mass transport of the Hg$^{2+}$ ions during both the deposition and stripping steps without the use of any mechanical stirrers or rotating electrodes. This leads to a larger anodic current, thus obtaining higher detection sensitivity for the determination of mercury (II) ions. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:31AM |
KI.00007: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2007 9:31AM - 9:44AM |
KI.00008: Breakup of micro liquid jets in crossflow Jaiho Lee, Khaled Sallam An experimental research for the breakup of micro liquid jets in crossflow was performed by digital inline holographic microscopy (DIHM) using a commercial CCD sensor (Nikon D-70). DIHM is similar in setup to standard in-line digital holography except no lens is used to collimate the object beam. This eliminates two lenses from the typical optical path used for in-line holography, which results in a much cleaner hologram recording and reconstruction. In the present experimental setup, two Nd:YAG lasers were used to generate two independent laser pulses. The laser intensity was controlled by two $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ wave plates and a polarized beam splitter cube. The laser beams were expanded with an objective lens (M 5x) and a 15 $\mu $m pinhole. Double pulsed holograms were recorded on the same camera frame. Velocities of micro liquid jets have been determined by the time interval between two pulses and the distance between double pulsed images on a camera frame. The velocity results had good agreement with theoretical results. Moreover, various Reynolds numbers (Re = 1754 $\sim $5282) were used for breakup regime transitions of micro liquid jets. [Preview Abstract] |
Tuesday, November 20, 2007 9:44AM - 9:57AM |
KI.00009: A New Low Reynolds Number Facility for Active Flow Control Applications Matthew Munson, William Dickson, Morteza Gharib, Tim Colonius In pursuit of integrated closed-loop flow and flight control for stabilization and regulation of vortex formation in separated flows, a new low Reynolds number facility has been designed and installed at the Graduate Aeronautical Laboratories at California Institute of Technology. Observations of insect flight show intriguing high-lift mechanisms that rely heavily on stabilization of leading-edge vortex (LEV) structures. A multi-disciplinary research initiative (MURI) has been formed in order to explore the benefits of understanding and manipulating this LEV stabilization process for micro air vehicle applications. Flow control work at higher Reynolds numbers provides a strong likelihood that mass injection control strategies will be able to strongly influence vortex shedding and result in lift enhancement. This presentation discusses the design features that makes this facility uniquely suited to pursue these investigations. Additionally, preliminary experiments aim to determine the effect of various actuation schemes on the lift characteristics of a low Reynolds number, low aspect-ratio airfoil model. [Preview Abstract] |
Tuesday, November 20, 2007 9:57AM - 10:10AM |
KI.00010: Development of Hydrodynamic Flow Control using Combined Hydrophobic and Hydrophilic Coatings and Micelle Polymer Hirotaka Sakaue, Katsuaki Morita, Tsuyoshi Hyakutake, Hiroyuki Nishide Development of hydrodynamic flow control using combined hydrophobic/hydrophilic coatings and micelle polymer is discussed. The former is developed for a passive flow control, while the latter for an active flow control. First, a passive flow control of this method is shown by applying hydrophobic and hydrophilic coatings separately on a control surface. Drop tests of an ogive shape model in water tower show that the resultant coating varies the drag coefficient, indicating the ability to control the speed. In the final version, hydrophobic and hydrophilic coatings will be separately applied parallel to the dropping direction to demonstrate the direction control using this method. Second, as an active flow control, a temperature-sensitive micelle polymer of poly(isopropyl acryl amide) [poly(NiPAAm)] is shown. This polymer is hydrophobic over the critical temperature of 32$^{\circ}$C, while it is hydrophilic below the critical temperature. In the final version, this polymer will be applied to the model surface to demonstrate the capability of an active flow control. [Preview Abstract] |
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