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한희갑,권영필 崇實大學校 生産技術硏究所 1996 論文集 Vol.26 No.1
Edgetone or cavitytone is a typical vortex sound generated by the interation of a vortex with a solid surface. For low Mach number flow this vortex sound has been an interesting research topic in hydrodynamics and acoustics because intensive noise or pulsating flow is induced. The purpose of this study is to make the quantitive model for the frequency characteristics of edgetone which was generated by two dimensional impinging jet on a circular cylinder and to establis a theoretical model for the directivity of a adiation sound field. First, the experiment for frequency characteristics is conducted and analyzed by using a feedback theory. And then a position of the effective sound source is obtioned. Second, it is experimented for an imponging tone by normal well. And the comparitive study on the frequency characteristics is performed. In result, a position of the effective sound source is proved. Also, the directivities of radiation sound source for a cylinder and a plane wall are respectively measured and examined.
권영필 崇田大學校 1981 論文集 Vol.11 No.1
The one-demensional approximation for fin problems is widely used in currint texts and industial pratice. The errors caused by this approximation is analysed numerically by the finite element method. Two dimensional solution is obtained by the FEM and compared with the one dimensional solution. The results show that the one dimensional approximation is reasonable when the Biot number is as amall as 0.01 but that when the Biot number is as large as 1.0 the error in total fin heat transfer is a few tem percent.
권영필,이주원,이동훈,Kwon, Y.P.,Lee, J.W.,Lee, D.H. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.2
A strong combustion-driven sound from a surface burner made of a perforated metal fiber plate for premixed gas was investigated to clarify the physical mechanism of its generation. A simple model was developed for the acoustic power generation in terms of the heat transfer response function and the acoustic impedance of the burner. The acoustic impedance of the perforated metal fiber placed on the open exit was measured and the heat release response of the burner to the oscillating flow associated with the acoustic disturbance was expressed in terms of a response function. It was found that the power is generated by the heat release in response to the downstream particle velocity, in contrast to the upstream velocity in the case of the Rijke oscillation driven by a heater placed in the lower half of a columm with upstream flow. The measured frequencies of the oscillation were in agreement with the estimated resonance frequencies and their excitation was varied with the combustion conditions. For the same fuel rate, the excited frequency increases with the air ratio if it is low but decreases with the ratio if not so low. Such frequency characteristics were explained by assuming a heat release response function with a time constant and it was shown that the excited frequency decreases as the time constant increases.
권영필,Gwon, Yeong-Pil 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.3
The phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet-edge interaction model which is based on the substitution of an array of dipoles for the reaction of the wedge to the impinging jet. The edgetone is produced by the feedback loop between the downstream-convected sinuous disturbance and upstream-propagating waves generated by the impingement of the disturbance on the wedge. By estimation of the phase difference between the downstream and the upstream disturbances, the relationship between the edge distance and the wavelength is obtained according to the phase-locking condition at the nozzle lip. With a little variation depending on the characteristics of jet-edge interaction, the criterion can be approximated as follows: h/.LAMBDA. + h/.lambda. = n - 1/4, where h is the stand-off distance between the nozzle lip and the edge tip, .LAMBDA. is the wavelength of downstream-convected wave, .lambda. is the wavelength of the upstream-propagating acoustic wave and n is the stage number for the ladder-like characteristics of frequency. The present criterion has been confirmed by estimating wavelengths from available experimental data and investigating their appropriateness. The above criterion has been found to be effective up to 90.deg. of wedge angle corresponding to the cavitytones.