Papers by Keyword: Laser Doppler Anemometry

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Authors: Wen Yuan Fan, Xiao Hong Yin
Abstract: The Laser Doppler anemometry was employed to determine quantitatively the liquid velocity induced by the successive rising of single bubble in non-Newtonian carboxymethylcellulose (CMC) aqueous solutions under various experimental conditions of mass concentration solutions, measures heights and gas flow rate. The features of liquid motion in the region of bubble rising channel were investigated by analysis the liquid velocity pulsation using fractal theory. The results show that the liquid motion in the channel zone of bubble rise has a special feature of double fraction, and shows strong positive persistence characteristics for a small delay, but the positive persistence characteristics begins to reduce obviously with the increase of the delay, and even presents the anti-persistence for some measured points.
Authors: H. Wu, Michael N. Morgan, Bin Lin
Abstract: The boundary layer of air rotating with the grinding wheel can result in fluid starvation in the contact region. The boundary layer acts a barrier to fluid penetration and prevents fluid reaching the contact region and the fluid is deflected elsewhere. Such a situation is inefficient and wasteful. This work reports on an investigation of the air boundary layer aimed at increasing understanding of boundary layer for development of improved fluid delivery systems. The work reported focuses on the outcomes of experimental tests using the Laser Doppler Anemometry technique. Three velocity components of the air flow around the periphery of a rotating grinding wheel were measured for a range of wheel speeds. The contour distribution of the velocity and the turbulent distribution of velocity clearly show the air flow motion around the grinding wheel.
Authors: Yung Chung Chen, Zhao Cheng Chen, Tung Wu Lu, Chien Ming Chen
Abstract: We designed a new module of Laser Doppler Anemometry (LDA) with fiber optical system, which is mainly comprised of a laser diode, optical fibers and a two dimensional (2D) photodetector. The fiber optical system involved a laser diode (VCSEL, Copax Inc.) with 850 nm wavelength, single mode fiber (Prime Optical Fiber Inc.), half coupler and two fiber collimators. The 2D photodetector made by silicon PIN photodiode is aligned between the two collimators with 39° beams cross angle and all the components were set into a rectangle case, which have coin’s size and can be accommodated by two same set of these components. We added anticoagulant and antiseptic into fresh chicken blood and diluted it with normal saline, and then put the diluted blood into a beaker with a motor in the liquid. The diluted blood was pumped by the motor into an aqueduct which is connected to glass aqueduct, and back to the beaker to form a circulation system. In the experiments, we evaluate the relationships among the blood cell velocity and diameter of glass tube, temperature variation of blood, and concentrations of blood. By analyzing the results of these experiments, the main factor that affects the precision of velocity measurement is the cross angle of two injected laser beams and the intensity of scattering light. The module constructed by optical fiber light can precisely measure the velocity of blood flow at most 5% error.
Authors: Wen Yuan Fan, Xiao Hong Yin
Abstract: The dynamics of bubble generating in carboxymethylcellulose (CMC) aqueous solution were studied using chaos method. The results show that for low position (P) and gas flowrate (Qg), the characteristic frequency of axial and radial velocities are both consistent to bubble periodic shear frequency; but for high position, power spectrums are of broad coverage within low frequency range. The magnitudes of radial characteristic peaks increase with gas flowrate. Phase portraits of reconstructed phase space of velocity time series display certain features of chaotic attractor. For low P and Qg, phase portrait takes on uniform elliptical shape due to liquid periodic motion caused by bubble periodic rising. Whereas for high P and Qg, the liquid turbulence is reinforced by bubble increasing velocity and large-scale turbulent intensity around bubble increases, consequently, leading to significant compression of phase portrait.
Authors: Liang Jie Li, Long Biao He, Xue Jing Wang, Ping Yang
Abstract: Abstract. To realize the sound pressure unit directly, the method of sound pressure measurement based on acoustic particle velocity was described. In order to get a simple acoustic field, a travelling wave tube was designed. The sound pressure distribution obtained by microphone along the tube was measured. The result showed the acoustic field inside the tube could be considered as travelling wave and the sound pressure is equal to the product of the air density, sound speed and the particle velocity. The laser Doppler Anemometry was used to measure the particle velocity in the acoustic field. The modulated Doppler signal was obtained by measurement system. With the spectral analysis of Doppler signal and the signal model, the particle velocity was obtained with the Bessel function analysis. The comparison of sound pressure measured by microphone and the value deduced from the velocity measured by laser Doppler system shows that deviations between two methods were 0.04 dB at 650 Hz and discrepancies were less than 0.34 dB at frequencies from 300 Hz to 1k Hz.
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