• 대한기계학회논문집B
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• 제23권5호
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• pp.603-609
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• 1999

The effect of an external acoustic excitation on the wake structure behind a circular cylinder was experimentally investigated. The sound wave was excited in the frequency range of the shear layer instability and two sound pressure levels of 114 and 120dB were used in this study. As a result, the acoustic excitation modified the wake structure by increasing the velocity fluctuation energy without changing the vortex shedding frequency. The acoustic excitation enhanced the vortex shedding process and promoted the shear layer instability. Consequently, the acoustic excitation reduced the length of the vortex formation region and decreased the base pressure. In addition, the vortex strength of vortices was increased and the width of the wake was spread out due to the acoustic excitation. When the excitation frequency was identical to the shear layer instability frequency, the effect of the external flow control on the cylinder wake was maximized. In addition, with increasing the sound pressure level, the effect of the external acoustic excitation on the wake structure increased.

• 대한기계학회논문집
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• 제11권3호
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• pp.362-367
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• 1987

본 연구에서는 위의 인자들 중 .int.Pdt대신에 계산의 편의상 .int.Pd.theta.로, .DELTA.P는 최고압력차의 영향이 가장 크다고 생각되어 (.DELTA.P)$_{max}$를 대상으로 하여 이들 제인 자와 각 주파수성분과의 상관관계에 대하여 검토하고, 주파수역에 대하여 미치는 영향 을 정량적으로 해석하기 위하여 보조 프로그램을 작성하였다.

• International Journal of Fluid Machinery and Systems
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• 제6권3호
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• pp.121-136
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• 2013

This paper reports the 1-D fluid transient simulation results of the discharge flow conditions in a 6-cylinder reciprocating slurry pump. Two discharge manifold configurations are studied comparatively; a case with a hexagon shaped discharge manifold where each cylinder discharges at a single vertex, and a case where all the cylinders discharges are lumped together into a tank shaped manifold. In addition, the study examines the effect of two pulsation mitigation measures in the case of hexagonal manifold; a single inline orifice in one of the hexagon sides and a volumetric dampener at the manifold outlet. The study establishes the pressure and flow fluctuation characteristics of each configuration and decouples the pulsation characteristics of the pump and the discharge manifold.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.342-352
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• 2003

Idle NVH characteristics are one of the most important aspects among the vehicle performances. Vehicle developers are devoted to improve vehicle interior noise and steering wheel and seat vibrations. In order to improve the idle quality, noise and vibration transfer path should be carefully evaluated. Also, effects of various components related to the idle performance should be confirmed. A general procedure for improving the idle qualify is described in detail. The relationship among cylinder pressure characteristics, crankshaft rotational speed variation, and vehicle vibrations is also investigated. Influences of drive shaft, torque converter, air conditioning system, vehicle structure including engine mount system, and idle control parameters on the vehicle idle quality are studied. Weak points of typical vehicles on the idle qualify are identified. Some of improvement measures are proposed and verified.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.82-93
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• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.

• 항공우주시스템공학회지
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• 제8권3호
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• pp.1-5
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• 2014

An inner flow of a porous cylinder with partial slots was visualized to study fluidic phenomena in a solid rocket motor. A high-pressure chamber and an air supply system for high flow rate were used. In order to visualize the inner flow, the smoke generator with a cam-driven pump and heaters and high speed camera were adopted. The results of the cylinder type and the partial slot type were compared. As a result, the injected smoke flow in the partial slot type had circumferential fluctuations unlike the cylinder type. It was found that the circumferential flow induced from the partial slots could be the cause of combustion instability and roll torque.

• 오토저널
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• 제12권3호
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• pp.30-40
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• 1990

The computer program for the prediction of the volumetric efficiency of 4-cycle single cylinder diesel engine was developed using the characteristic method which considers the effects of friction, heat transfer and specific heat. The results of calculation by this program are as follows; 1. The back flowing was arised at the beginning and the closing stage of inlet valve, and the back flowing mass and velocity decrease as the engine speed increases. 2. The volumetric efficiency varies with the engine speed and the length of inlet manifold. There was an optimum length of inlet manifold for each specified engine speed. 3. The pressure fluctuation and friction effect in the inlet manifold became very important factors for the determination of the volumetric efficiency.

• 한국유체기계학회 논문집
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• 제13권3호
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• pp.5-11
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• 2010

As a basic study of the aero-acoustic noise, Large eddy simulations were carried out for a fixed circular cylinder at Renolds number (Re=$9.0\times10^4$) using commercial CFD code, FLUENT. The subgrid-scale turbulent viscosity was modeled by Smagorinsky-Lilly model adapted to structured meshes. The results of analysis showed that time-averaged value, $\bar{C}_D$ is approximately 1.47 which is considerably adjacent with the experimentally measured value of 1.32 in comparison to the values performed by previous researchers. It is observed that there are the very small acoustic pressure fluctuation with the same frequency of the Karman vortex street.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.654-657
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• 2014

In this paper, we study the analytical method to predict the excitation forces for the engine system. The engine system on the construction equipment is one of the important power sources, and the characteristics of the engine decide the performance of noise and vibration for the equipment. We predict the excitation forces using the geometrical data of the crank system and the combustion pressure in the cylinder. The excited forces are represented by the torque fluctuation above the center of the crank shaft.

• 동력기계공학회지
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• 제9권3호
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• pp.26-32
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• 2005

The volumetric efficiency is significantly affected by the behavior of pressure wave in induction system and exhaust pipe. By the motion of the piston, there exist pressure fluctuation in induction system which produce waves. Waves are propagated along a pipe bi-directional as they propagated through it, making compression wave and rare-faction(expansion) wave. These wave phenomena can affect to the volumetric efficiency. As a method of improvement of the volumetric efficiency, fuel economy and pollutant emission reduction particularly in low engine speeds, a side-branch additional tunable helmholtz resonator on the secondary pipe of intake system is proposed by use of their acoustic vibrations. Some of results are presented which deal with their physical phenomena for the wave action of intake system in a four-stroke three cylinders diesel engine.