• 대한기계학회논문집B
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• 제26권2호
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• pp.219-226
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• 2002

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7 Corresponding to a wake-passing through the cascade, two velocity deficits appeared near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit was caused by a periodic wake and the second one appeared after some delayed time. The second velocity deficit was interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreased the duration time of separation appearance and the lesser losses of blade were resulted.

• 동력기계공학회지
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• 제2권3호
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• pp.15-20
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• 1998

An integrated computing system has been developed for a Navier-Stokes design procedure of an axial-flow compressor blades. The process is done on the four separate steps, i.e., determination of the basic profiles, generation of computational grids, cascade flow simulation and analysis of the computed results in design sense. Applications are made to the blade design of the LP compressor. Computational results are analyzed with respect to the flow-field characteristics and are compared with the expected design requirements. The present system are coupled with the design procedure of the turbomachinery blades using the Navier-Stokes technique.

• 대한기계학회논문집
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• 제15권1호
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• pp.229-240
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• 1991

본 연구에서 사용한 이론과 제시된 방법의 타당성을 검토하기 위하여 익열 간 극이 무한대인 단일 익형 주위의 유동장을, 최근에 개발된 계산방법인 Lambda방법을 사용한 Dadone의 해석결과와 비교하였고, 범용의 압축기 익형인 NACA65게열 익열 유동 에 대한 Herrig의 실험값, 그리고 미분해석에 의한 점성-비점성 상호작용 방법을 사용 한 Hansen의 계산값고, 이들 조건과 동일한 상태에서 본 연구에서 제시한 방법으로 계 산한 결과와 만족할 만한 일치를 얻었다.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.263-269
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• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.812-817
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• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

• 대한기계학회논문집B
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• 제25권2호
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.121-124
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• 2006

The arteries are very important in cardiovascular system and easily adapt to varying flow and pressure conditions by enlarging or shrinking to meet the given hemodynamic demands. The blood flow in arteries is dominated by unsteady flow phenomena due to heart beating. In certain circumstances, however, unusual hemodynamic conditions cause an abnormal biological response and often induce circulatory diseases such as atherosclerosis, thrombosis and inflammation. Therefore quantitative analysis of the unsteady pulsatile flow characteristics in the arterial blood vessels plays important roles in diagnosing these circulatory diseases. In order to verify the hemodynamic characteristics, in-vivo measurements of blood flow inside the extraembryonic arterial bifurcation cascade of chicken embryo were carried out using a micro-PIV technique. To analyze the unsteady pulsatile flow temporally, the (low images of RBCs were obtained using a high-speed CMOS camera at 250fps with a spatial resolution of $30{\mu}m\times30{\mu}m$ in the whole blood vessels. In this study, the unusual flow conditions such as flow separation or secondary flow were not observed in the arterial bifurcations. However, the vorticity has large values in the inner side of curvature of vessels. In addition, the mean velocity in the arterial blood vessel was decreased and pulsating frequency obtained by FFT analysis of velocity data extracted in front of the each bifurcation was also decreased as the bifurcation cascaded.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.392-397
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• 2001

A numerical study is performed to investigate the interaction between subsonic axial turbine blade boundary layer and periodically oncoming rotor induced wakes. An implicit scheme for solving the compressible Navier-Stokes equation is developed, which adopts a 4th-order compact difference for spatial discretiztion, a 2nd order Crank-Nicolson scheme for temporal discretization and the dynamic eddy viscosity model as the subgrid scale model. The efficiency and the accuracy of the proposed method are verified by applying to some benchmark problems such as laminar cylinder flow, laminar airfoil cascade flow and a transitional flat plate boundary layer flow. Computational results show good agreements with previous experimental and numerical results. Finally, flow through a stator cascade is simulated at $Re = 7.5{\times}10^5$ without free-stream turbulence intensity. The velocity fields and skin friction coefficients in the transitional region show similar trends with previous boundary layer natural transition.

• 대한기계학회논문집
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• 제17권2호
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• pp.445-451
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• 1993

For the calculation of transonic laminar flow fields in cascades of turbomachinery, a finite volume method employing Jameson's Runge-Kutta integration scheme as a basic algorithm is presented. The cell-vertex scheme introducing half-spacing mesh cells is developed. For the velocity gradients in the stress terms the integration with divergence theorem is used for the average concept. Some numerical results show good agreement with experimental data.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3639-3648
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• 1996

The effect of 15% pinched diffuser in a centrifugal air compressor with a cascade airfoil diffuser on the aerodynamic performance is investigated using a numerical approach. The commercial CFD code for three-dimensional, turbulent, compressible flow fields is executed for various mass flow rates at a design speed which can be obtained as long as the calculation succeeds. The pinched diffuser is found to help improve the instability of flow within vaneless diffuser space, especially the reverse flow near shroud, and to change both stall/surge line and choking line to increase the surge margin. It is also found to generate more favorable increase of static pressure in diffuser region, and to increase the resulting pressure ratio and efficiency.