Computational Elements for High-fidelity Aerodynamic Analysis and Design Optimisation

The study reviews the role of computational fluid dynamics (CFD) in aerodynamic shape optimisation, and discusses some of the efficient design methodologies. The article in the first part, numerical schemes required for high-fidelity aerodynamic flow analysis are discussed. To accurately resolve high-speed flow physics, high-fidelity shock-stable schemes as well as intelligent limiting strategy mimicking multi-dimensional flow physics are essential. Exploiting these numerical schemes, some applications for 3-D internal/external flow analyses were carried out with various grid systems which enable the treatment of complex geometries. In the second part, depending on the number of design variables and the way to obtain sensitivities or design points, several global and local optimisation methods for aerodynamic shape optimisation are discussed. To avoid the problem that solutions of gradient-based optimisation method (GBOM), are often trapped in local optimum, remedy by combining GBOM with global optimum strategy, such as surrogate models and genetic algorithm (GA) has been examined. As an efficient grid deformation tool, grid deformation technique using NURBS function is discussed. Lastly, some 3-D examples for aerodynamic shape optimisation works based on the proposed design methodology are presented.Defence Science Journal, 2010, 60(6), pp.628-638, DOI:http://dx.doi.org/10.14429/dsj.60.58

Roles of CFD Simulations in Developing Rocket Propulsion System

This paper focuses on the role of CFD in developing rocket propulsion system by simulating major devices such as turbopump inducer, cryogenic storage tank and solid rocket propellant. These are closely related to operation reliability and fuel efficiency of rocket propulsions system. The numerical computations on these devices have several issues owing to complex flow physics such as interaction between fluid, structure, and combustion domain or extreme flow conditions. This paper introduces these issues and corresponding numerical methods for more realistic simulation. Finally, several numerical results are presented to show the contributable aspects of CFD in rocket development stage.http://www.i-asem.org/publication_conf/structures16/0.Keynote/T1C.k1102F.pdfOAIID:RECH_ACHV_DSTSH_NO:A201606328RECH_ACHV_FG:RR00200003ADJUST_YN:EMP_ID:A001138CITE_RATE:FILENAME:T1C.k1102F.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:FILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/ce957928-d752-4908-b42d-63d3846948e1/linkCONFIRM:

ACCURATE AND EFFICIENT RIEMANN SOLVER FOR EULER AND NAVIER-STOKES EQUATION

The present paper deals with an improvement of efficient and accurate numerical flux schemes for the hyperbolic conservation laws of aerodynamics. Due to numerical approximation and linearization, many flux schemes suffer shock instability and unwanted oscillations. The proposed schemes, called AUSMPW+ and RoeM, cure these problems and numerical tests show the robustness, accuracy and efficiency of both flux schemes

URANS Computations of Cavitating Flow around a 2-D Wedge by Compressible Two-Phase Flow Solver

This paper deals with the computation of unsteady cavitating flow around a twodimensional wedge by using Unsteady Reynolds Averaged Navier-Stokes (URANS) flow solver. Because of accuracy deterioration problem due to excessive numerical dissipations for low Mach number unsteady flow, properly scaled RoeM and AUSMPW+ numerical flux schemes are used to accurately compute unsteady cavitating flow. Fast Fourier Transform (FFT) analysis results of experiments and computations are compared to show similar dominant frequencies of shedding vortices. Shedding pattern and location of vortices are also compared to show similar behavior of each flow result.OAIID:RECH_ACHV_DSTSH_NO:A201606327RECH_ACHV_FG:RR00200003ADJUST_YN:EMP_ID:A001138CITE_RATE:FILENAME:M2J.1.AS733_1588F1.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:FILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/d3e93894-8ef1-4bce-9dfe-e2c270ced9d8/linkCONFIRM:

Multi-dimensional Limiting Strategy for Higher-order CFD Methods - Progress and Issue (Invited)

The present paper deals with the progress of multi-dimensional limiting process (MLP) and discuss the issues for further improvements. MLP, which has been originally developed in finite volume method (FVM), provides an accurate, robust and efficient oscillationcontrol mechanism in multiple dimensions for linear reconstruction. This limiting philosophy can be hierarchically extended into higher-order Pn approximation or reconstruction. The resulting algorithm, called the hierarchical MLP, facilitates the capturing of detailed flow structures while maintaining the formal order-of-accuracy in smooth region and providing accurate non-oscillatory solutions across discontinuous region. This algorithm has been developed within the modal DG framework, but it also can be formulated into a nodal framework, most notably the CPR framework. Troubled-cells are detected by applying the MLP concept, and the final accuracy is determined by the projection procedure and the hierarchical MLP limiting step. Through extensive numerical analyses and computations ranging from scalar conservation laws to fluid systems, it is demonstrated that the proposed limiting approach yields the outstanding performances in capturing compressible inviscid and viscous flow features. Further issues are also mentioned to improve and extend the current approach for higher-order simulations of high-Reynolds number compressible flows.Authors appreciate the financial supports by the EDISON program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2011-0020559) and by NSL (National Space Laboratory) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (NRF-2014M1A3A3A02034856). This work is also partially supported by the RoK ST&R project of Lockheed Martin Corporation. Authors also appreciate the computing resources provided by the KISTI Supercomputing Center(KSC-2014-C3-054).OAIID:RECH_ACHV_DSTSH_NO:420150000004648007RECH_ACHV_FG:RR00200003ADJUST_YN:EMP_ID:A001138CITE_RATE:FILENAME:6.2015-3199.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:FILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/a984d649-4b23-435b-adc9-df9aa0c8aa46/linkCONFIRM:

Computational elements for high-fidelity aerodynamic analysis and design optimisation

The study reviews the role of computational fluid dynamics (CFD) in aerodynamic shape optimisation, and discusses some of the efficient design methodologies. The article in the first part, numerical schemes required for high-fidelity aerodynamic flow analysis are discussed. To accurately resolve high-speed flow physics, high-fidelity shock-stable schemes as well as intelligent limiting strategy mimicking multi-dimensional flow physics are essential. Exploiting these numerical schemes, some applications for 3-D internal/external flow analyses were carried out with various grid systems which enable the treatment of complex geometries. In the second part, depending on the number of design variables and the way to obtain sensitivities or design points, several global and local optimisation methods for aerodynamic shape optimisation are discussed. To avoid the problem that solutions of gradient-based optimisation method, (GBOM) are often trapped in local optimum, remedy by combining GBOM with global optimum strategy, such as surrogate models and genetic algorithm (GA) has been examined. As an efficient grid deformation tool, grid deformation technique using NURBS function is discussed. Lastly, some 3-D examples for aerodynamic shape optimisation works based on the proposed design methodology are presented.OAIID:oai:osos.snu.ac.kr:snu2010-01/102/0000004648/3SEQ:3PERF_CD:SNU2010-01EVAL_ITEM_CD:102USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:.304FILENAME:Computational Elements for High-Fidelity Aerodynamic Analysis and Design Optimisation.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:YCONFIRM:

Computations of Compressible Two-phase Flow using Accurate and Efficient Numerical Schemes

RoeM and AUSMPW+ schemes are two of the most accurate and efficient schemes which are recently developed for the analysis of single phase gas dynamics. In this paper, we developed two-phase versions of these schemes for the analysis of gas-liquid large density ratio two-phase flow. We adopt homogeneous equilibrium model (HEM) using mass fraction to describe different two phases. In the Eulerian-Eulerian framework, HEM assumes dynamic and thermal equilibrium of the two phases in the same computational mesh. From the mixture equation of state (EOS), we derived new shock-discontinuity sensing term (SDST), which is commonly used in RoeM and AUSMPW+ for the stable numerical flux calculation. The proposed two-phase versions of RoeM and AUSMPW+ schemes are applied on several air-water two-phase test problems. In spite of the large discrepancy of material properties such as density, enthalpy, and speed of sound, the numerical results show that both schemes provide very satisfactory solutions.OAIID:oai:osos.snu.ac.kr:snu2006-01/104/0000004648/17SEQ:17PERF_CD:SNU2006-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:Computations_of_Compressible_Two-phase_Flow_using_Accurate_and_Efficient_Numerical_Schemes.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Numerical Simulation of the Interaction between Slender Body Vortices and a Fin

The interaction between slender body vortices and a single fin located down the axis of the body is investigated numerically for angle of attack of 30 deg. and Reynolds number of 6000. The present research includes a parametric study on the effects of fin axial and azimuthal positions on the development of the vortex system. A numerical method based on the pseudo-compressibility is used for solving the three-dimensional incompressible Navier-Stokes equations using Lower-Upper Symmetric Gauss-Seidel implicit scheme. The numerical results show that the vortices remain very coherent and attached to the body until they reach the fin section where they become less coherent and begin to separate from the body. Also, the result shows that the fin location does not affect the upstream development of the vortices but it does affect the location at which the vortices separate from the body. The effect of azimuthal fin positions was also investigated. As azimuthal angle of the fin increased, the size of the vortex on the port side decreased, but the starboard side vortex grew in size and moved across the leeward ray to the port side. The computed results are found to agree well with the experimental data

Discrete Adjoint Approach for Aerodynamic Sensitivity Analysis and Shape Optimization on Overset Mesh System

In the present talk, the strategies to apply the sensitivity analysis method to aerodynamic shape optimization problems of complex geometries are intensively discussed. To resolve the design of complicated aircraft geometries such as high-lift devices, wing/body configurations, overset mesh techniques are adopted. In addition, a noticeable sensitivity analysis method, adjoint approach, which shows very good efficiency and accuracy for aerodynamic design problems, is also introduced. For the incorporation of the adjoint method into the overset mesh system, adjoint formulations are derived for the overset boundary conditions based on linear interpolation. The feasibility of non-conservative adjoint overset boundary conditions for external flow applications is carefully investigated by comparison with a single block design result for the same geometry. Through the several design application problems for realistic aircraft geometries, the present design framework demonstrates its capability and applicability for aerodynamic design of complex geometries.This work was supported by the second stage of the Brain Korea 21 Project in 2008

IMPROVEMENT OF VORTEX GENERATOR SOURCE MODEL FOR ADJOINT-BASED DESIGN OPTIMIZATION

The present paper deals with a vortex generator source model for the adjoint-based design optimization. To efficiently design the vortex generator inside an S-shaped subsonic inlet, the vortex generator source model is employed instead of the fully gridded vortex generator. The previously developed original source model, however, does not reflect a small change in position and thus has difficulties in differentiation for sensitivity analysis. For this reason, the original source model is modified into a differentiable source model. Through the differentiable source model, a large number of design variables including vortex generator position can be treated with an adjoint variable method. After the optimization with the design variables of the chord length, height, angle of incidence, axial and circumferential positions of each vortex generator, the performance of the target inlet is remarkably improved, showing that the distortion coefficient well over 70% while maintaining the total pressure recovery ratio.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0027486).OAIID:oai:osos.snu.ac.kr:snu2012-01/104/0000004648/16SEQ:16PERF_CD:SNU2012-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:IMPROVEMENT_OF_VORTEX_GENERATOR_SOURCE_MODEL_FOR_ADJOINT-BASED_DESIGN_OPTIMIZATION.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]: