• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.8-17
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• 2005

It is well known that preconditioning methods are efficient for convergence acceleration in the compressible low Mach number flows. In this study, the original Euler equations and three differently nondimensionalized preconditioning methods are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as numerical flux discretization and time integration, respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning allows Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.18-27
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• 2002

Aerodynamic shape optimization of two-dimensional airfoils in inviscid compressible flows is performed using a continuous adjoint formulation on unstructured meshes. Accurate evaluation of the gradient is achieved by using a reconstruction scheme based on the Laplacian averaging. A least-square method with extended stencil is used for flow gradient calculations. Proper convergence criterion is studied on Euler and adjoint equations for efficient design. The present method has been applied to RAE2822 and NACA0012 airfoils such that wave drag can be minimized by removing the shock wave. An inverse design is also performed to recover the shock wave on the designed RAE2822 airfoil.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.229-240
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• 1991

The large camber angle theory of turbomachine blade of compressor has been developed recently for the two-dimensional flow by Hawthorn, et al. However, in the above theory it was assumed that the fluid was incompressible and inviscid, and the blades had no thickness. In this study, the flow in a blade cascade being mounted in parallel fashion with blade of arbitrary thickness is studied in order to determine the effects of the camber angle on the performance characteristic of the blade section under the consideration of compressibility and viscosity of fluid. The panel method is used for potential flow analysis. The flow in the boundary-layer is obtained by solving the integral boundary-layer structure through the laminar, transitional , and turbulent flow using the pressure field determined from the potential flow. And then the viscous-inviscid interaction scheme is used for interaction of these two flows. For the determination of the variation in the outlet fluid angle influenced by deviation in cascade flow, the superposition method which is used for single foil is introduced in this analysis. By the introduction of this method, the effects of the deviation on outlet fluid angle and the resulting fluid angle are made to adjust for oneself through the calculation. As the result of this study, the blade of large camber angle, large incidence angle, large pitch-chord ratio has large viscous and compressible effect than those of small camber angle. Lift force increase as camber angle increases, but above 60.deg. of camber angle, lift force decrease as camber angle increases. But drag force increases linearly with camber angle increases in the entire region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.1044-1051
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• 1989

A numerical calculation is carried out for the analysis of 3-dimensional compressible flow field in axial-flow rotating blades by using finite element method. The calculation of flow in impellers plays a dominant role in the theoretical research and design of turbomachines. Three-dimensional flow fields can be obtained by the quasi-three-dimensional iterative calculation of the flows both on blade-to-blade stream surfaces and hub-to-shroud stream surfaces with the introduction of viscous loss model in order to consider a loss due to viscosity of fluid. In devising the loss model, four primary sources of losses were identified: (1) blade profile loss (2) end wall loss (3) secondary flow loss (4) tip-leakage loss. For the consideration of an axially parabolic distribution of loss, the results of present calcullation are well agreed with the results by experiment, thus the introduction of loss model is proved to be valid.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.277-280
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• 2006

This paper describes the aerodynamic interference characteristics between the ing and the engines in a commercial airplane which is realized by reverse engineering based on the photo measurement. Steady three-dimensional compressible inviscid Euler equation is solved in the unstructured grid system under the cruise condition. The lift and drag forces in the wing with engines increase by 1.49% and 3.9%, respectively compared with the wing without engines.

• Journal of computational fluids engineering
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• v.2 no.2
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• pp.51-58
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• 1997

A reliable computational solver has been developed for the analysis of three-dimensional inviscid compressible flows around a nacelle of a high bypass ratio turbofan engine, The numerical algorithm is based on the modified Godunov scheme to allow the second order accuracy for space variables, while keeping the monotone features. Two step time integration is used not only to remove time step limitation but also to provide the second order accuracy in a time variable. The multi-block approach is employed to calculate the complex flow field, using an algebraic, conformal, and elliptic method. The exact solution of Riemann problem is used to define boundary conditions. The accuracy of the developed solver is validated by comparing its results around the isolated nacelle in the cruise flight regime with the solution obtained using a commercial code "RAMPANT. "

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.28-35
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• 2002

In cavity flow, the rectangular step generates so strong sound that many researchers have investigated method to suppress the nois during interaction between vortical flow and rectangular forward step. In this study the flow noise from the vortex motion in two-dimentional low Mach number flow past a forward step with various chamfering angle is calculated numerically. Inviscid incompressible discrete vortex model and matched asymptotic expansion(MAE) theory are applied to obtain the inner flow field and the outer noise field. Both source acoustic pressure and sound intensity are obtained with various chamfering height, chamfering angle and initial vortex position. The pressure amplitude is most suppressed when the chamfering angle is between $15^{\circ}C$ and $30^{\circC}$ at the chamfering length of 30% of the step height.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1055-1065
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• 2009

In this study, stability analysis of boundary layers on airfoils is performed by using parabolized stability equations(PSE). Boundary layer edge conditions are obtained by compressible inviscid flow calculations. Mean velocity and temperature profiles of the laminar boundary layer are obtained by solving compressible boundary layer equations in generalized curvilinear coordinates with fourth order accuracy in the wall normal direction. Laminar mean flow profiles are used as input data for PSE to investigate growth rates of disturbances and stability characteristics. For the cases of boundary layer on NACA0012 and HSNLF(1)-0213 airfoils at Mach number 0.5, growth rates with respect to disturbance frequencies and profiles of disturbance amplitude are investigated. The effect of angle of attack on stability characteristics are examined at both upper and lower surfaces. The neutral stability curves, effect of Mach number and effect of airfoil section shapes are also analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.3
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• pp.213-220
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• 2014

A program that predicts trajectories of projectiles influenced by the interference flow field of helicopters is developed. The interference flow field are computed using a compressible inviscid solver in conjunction with an actuator disc model. The trajectories are predicted using 6-DOF (Degree of Freedom) equations as well as an alternative form of modified point mass equations of motion. The method for the interference flow field prediction method are validated with ROBIN(ROtor Body INteraction) model. A Sierra international bullet and a 105mm projectile are used to validate the trajectory method. Trajectories of a Sierra International bullet and a HYDRA 70 rocket firing from a helicopter are predicted.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1244-1253
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• 1990

Time-Marching methods solving Euler equations are used for calculation of two-dimensional, steady, inviscid flow through a stationary compressor cascade. Calculation method is based on the Denton`s opposed difference scheme. A smoothing in the axial direction is used to increase the stability of solution. The computational grid consists of quadrilateral elements, one of which has four nodes at each corner and the grid points on the upper periodic boundaries are located one pitch away from those on the lower boundaries to satisfy the periodicity condition. Results of calculation show good agreement with other computational and experimental results, proving that the present method of calculation should be applied with confidence for the cascade flow with shock wave.