• 대한기계학회논문집
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• 제12권1호
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• pp.106-115
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• 1988

본 연구에서는 경계층 유동을 충류, 천이, 난류 영역을 포함하는 압축성 유동으로 가정하였고, Morgan 등이 제시한 새로운 질점분할 방법을 사용하여 속도분포를 계산하고, 점성 압축성 효과를 고려하기 위하여 viscous--inviscid interaction 법을 사용하였고 이 계산 결과를 기존의 실험값과 비교하여,타당성을 확인하였다.그리고 최적 양력의 익형 설계는 Augmented Lagrange multiplier 법을 사용하였고 비구속 조건을 갖는 목적함수 augmented lagrangian의 최소화는 Davidan-Fletcher-Powell 방법 중 self-scaling quasi-Newton algorithm을 사용하였다. 그리고 NACA 23012를 기본 익형으로 하고 NACA 64-2-415, NACA 64-2-A215, NACA 65-3-218를 보상 익형으로 하여 최대 양력익형을 설계 하였다.

• International Journal of Aeronautical and Space Sciences
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• 제15권4호
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• pp.345-355
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• 2014

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.754-759
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• 2001

This paper presents unsteady computational investigations and wind tunnel tests on the flow field around a square cylinder with a gap between the body and the ground plane. Two-dimensional unsteady, incompressible Navier-Stokes codes are developed for the computation of the viscous turbulent flows. By computing the flow around a square cylinder without ground effect, three two-equation turbulence models are evaluated and the developed code is validated. The results show a good agreement with experimental values and other computational results. Critical gap height at which the formation of Karman vortex streets is interrupted, is demonstrated and another transition regime is pointed out

• 한국전산유체공학회지
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• 제11권3호
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• pp.64-70
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• 2006

A Computational study was carried out in order to investigate the moving wall effect of a circular cylinder at a Reynolds number of $2.0{\times}10^4$. The viscous-incompressible Navier-Stokes equations and Spalart-Almaras turbulent model of the commercial CFD code were adopted for this numerical analysis. The moving wall was set parallel with the freestream, and moving speed was equal to the freestream velocity. The gap ratio is defined as the distance ratio between the circular cylinder diameter and the height from the moving wall. The results show that there is vortex shedding over the critical gap ratio and aerodynamic loads including amplitude and the Strouhal number change according to the gap ratio.

• 한국해양공학회지
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• 제1권1호
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• pp.49-56
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• 1987

The dynamic behaviour of a marine riser was studied theoretically and experimentally. In linear analysis, the natural frequencies and mode shapes of the riser were obtained from the experiment and they were found to be in good agreement with theoretical results by using a simple asymptotic formula. In nonlinear ananlysis including viscous drag and large displacement, a numerical-perturbation technique based on the derived linear asymptotic solutions is used to predict the displacements and stresses of the riser in harmonic motion. These results were also compared with experimental data and found to be in general in good agreement.

• 한국해양공학회지
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• 제20권5호
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• pp.15-22
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• 2006

A finite-volume method using multi-block grid technique has been developed in order to investigate the flow field around multi-body. Here the matching grids are used at the interface between blocks and the boundary conditions are imposed there to exchange physical values across the interface. For the test problems, the laminar viscous flaw around one-and two-cylinder are simulated and the results are compared with experiments and other numerical results.

• 융복합기술연구소 논문집
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• 제5권1호
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• pp.37-40
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• 2015

Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan is carried out using the frequency domain panel method. Front rotor and rear rotor blades of a counter rotating axial fan are designed by using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. Performance characteristics of a counter rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

• 대한기계학회논문집
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• 제7권2호
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• pp.153-160
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• 1983

The flows in an axial flow turbomachine are calculated numerically in the two sets of flow surfaces of H-S and B-B surfaces assuming that the flow is axisymmetric. The calculation is performed by regarding the governing equations as the quasi-Poisson's equations and using the finite element method for the flow regions divided into triangular elements. The results of numerical calculation agree comparatively well with the experimental results and it has been found that the distribution of an axial velocity component at the rotor exit is not necessarily uniform under the influences of the inlet guide vanes and the front shape of the hub even if the rotor is designed by the free-vortex theory. Also it has been found that the existence of the optimum value of the blade number can be estimated from the results of calculation of deviation angles at rotor exit if we consider the viscous flow-loss, and that the flows of B-B surfaces are affected very sensitively by the degree of satisfaction of Kutta condition.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.243-249
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• 2001

Steady state flow calculations are executed for turbo-pump inducers of modem design to validate the performance of Tascflow code. Hydrodynamic performance is evaluated and structure of the passage flow and leading edge recirculation are also investigated. Calculated results show good coincidence with experimental data of static pressure performance and velocity profiles over the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main source of pressure loss. Amount of pressure loss from the upstream to the leading edge corresponds to that of pressure loss through the whole blade. The total viscous loss is considerably large due to the strong secondary flow.

• 한국해양공학회지
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• 제4권2호
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• pp.223-223
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• 1990

A circular cylinder is oscillated in th otherwise quiescent viscous fluid. Numerical analysis performed for this problem by using the fourth-order Runge-kutta method for the unsteady Navier-stokes equations. For K(Kelegan-Carpenter''s No.)=5, the flow developed symmetrically, while for K=10, it revealed random patterns. The coefficient of the rms force is overestimated by 20-30% compared with the experimental result.