• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.191-193
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• 2017

EFD-CFD Comparison Workshop was proposed based on the drag prediction workshop and high lift prediction workshop of AIAA. This workshop is organized to escalate the levels of wind tunnel test and computational fluid dynamics and to escalate the level of domestic aerodynamic technology through the collaboration of both areas. For three benchmark cases of which wind tunnel test results are available, comparison workshops have been held since 2015.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.1
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• pp.23-33
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• 2019

Unmanned Surface Vehicle (USV) is being developed to do maritime survey and maritime surveillance at Korea Research Institute of Ships & Ocean engineering (KRISO). The goal is that USV should be operated at the maximum speed of 45 knots and it should be operated at sea state 4. Therefore the planing hull of USV should be excellent in resistance performance and manoeuvring performance. It is needed to check its performance using Experimental Fluid Dynamics (EFD), Computational Fluid Dynamics (CFD) or analytic method before designing the hull. In this study, resistance performance was analyzed by EFD and CFD. EFD with heave and pitch was performed at high speed towing system in Seoul National University. CFD was performed using SNUFOAM based on openFOAM with dynamic mesh to calculate running attitudes. The results of CFD were compared with EFD results. The results of CFD were resistance, running attitudes and wave height. The flow distribution and pressure distribution were also analyzed. The results of numerical resistance was under estimated than EFD. Even though the results of CFD have a slight limitation, it can be successfully used to estimate the resistance performance of planing hull. In addition it can be used as a supplement for EFD results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.252-258
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• 2017

This paper describes on introduction of CASE 3 for EFD-CFD comparison workshop which is incharged of aerodynamic subcommittee of The Korean Societry or Aeronautical and Space Science. In addition, the results of candidate for CASE 3 were compared with experimental result and computational result. Currently, for this case 3, there are eight candidates from company, university and research institute. According to comparison of their results, they are in accordance with experimental data and computational data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.241-251
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• 2017

Computational fluid dynamics analysis was performed for the case 3 of the EFD-CFD workshop. Solvers were used for three commercial CFD codes(Star-CCM+, Fluent and CFX) and an open source CFD code(SU2). The grid were generated four types depending on the total cells using commercial grid generation code(Pointwise). Mach number of 0.4 and 0.8, 2 degree angle of attack and Mach number of 0.9, 1 degree angle of attack were calculated. Similar pressure coefficient curve and normal force coefficient were showed from the coarse grid to fine grid of four codes. But there is a difference in the drag coefficient. The position of the shock wave was predicted forward as the discretization order increased in calculations using Star-CCM+ and Fluent. The computation time to converge, Fluent, Star-CCM +, CFX are in order, and SU2 takes much time to converge.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.259-267
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• 2017

Flow fields around a KARI-11-180 airfoil, SDM and transonic body are numerically simulated by using an unstructured meshes based compressible flow solver developed at KAIST. RANS equations are solved to analyse the flow fields and Roe's FDS method is adopted to evaluate convective fluxes. Turbulence effect of the flow fields is modeled by a SA model, SST model and ${\gamma}-{\widetilde{Re}}_{{\theta}t}$ model. It is found that smaller drag coefficients are predicted for the KARI-11-180 airfoil when a transition phenomenon is considered and small deviations exist between CFD and EFD results. For the SDM, flow separation is observed at a leading edge and calculated aerodynamic properties show similar tendencies to experimental results. A shock wave on main wings of the transonic body is successfully captured by the present flow solver at a Mach number 0.9. Estimated pressure profiles by means of the present CFD method also agree well with those of wind tunnel results.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.6
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• pp.539-547
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• 2014

Ship squat is a well known phenomenon, which means an additional sinkage and a change of trim when a ship sails in shallow water. As a series of ship squat study, a HPMM(Horizontal Planar Motion Mechanism) test of KVLCC2 model ship to measure a sinkage and a trim in shallow water was conducted. Additionally a CFD(Computational Fluid Dynamics) analysis was carried out to simulate fluid flows around the ship surface. A change in ship speed, drift angle at three depth conditions(H/T = 1.2, 1.5 & 2.0) is considered for comparing these results. As a result, an increase of the ship speed and the drift angle caused an increase in ship squat in EFD(Experimental Fluid Dynamics), and created a lower pressure on the ship bottom area in CFD. Lastly the sinkage results of KVLCC2 by EFD and CFD are compared to results by three empirical formulas. The tendency of sinkage by EFD and CFD is similar to the results of empirical formulas.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.194-201
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• 2017

The KARI-11-180 airfoil was selected as a model for EFD-CFD comparison workshop case 1. Wind tunnel test for this model was conducted in KARI low speed wind tunnel with $0.6m{\times}3.0m$ model for the Reynolds number up to 3.0E6. The model configuration and wind tunnel test results including Cl, Cd and Cp were released at the KSAS 2015 spring conference. The computational analysis results with KFLOW, FLUENT and STAR-CCM+ were present in the KSAS 2015 fall conference. These computational works were summarized in this paper and the comparison results with each others including the wind tunnel data were also summarized.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.217-225
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• 2017

This research represents comparison and validation of static aerodynamic results in different wind tunnel organizations and EFD-CFD results. KAFA conducted wind tunnel tests with Standard Dynamics Model(SDM) which is based on the NRC model, the same configuration of KARI; and then compared and analyzed similarities and differences of the data from KARI and NRC results for verifying the accuracy of wind tunnel tests. Also, We compared the result of CFD with that of wind tunnel tests and examined strakes effect in static characteristics which are attached on the forward fuselage of SDM for investigating the cause of some discrepancies. From this analysis, there are some discrepancies in Cm tendency between EFD-CFD and it did not show the big difference of aerodynamic characteristics by strake effects. Thus, we need to research additionally for analyzing the different cause of some discrepancies such as vortex structures by the rear strut or intake of SDM and regenerating grid resolution of CFD.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.109-117
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• 2020

A structured grid system can be efficiently constructed by applying the patched-grid algorithm that alleviates many constraints of the conventional structured grid system. Three approaches were applied to case 4 of the EFD-CFD workshop: delta wing-cylindrical body shape to solve the existing grid generation problems and verify the results by comparing them with experimental data. Surface pressure distributions slightly differed from the experimental data at high angles of attack. The slope variation of the pitching moment with Mach number is analyzed and the variation can be explained with the tuck under phenomenon. In the supersonic region, the bow shock waves in front of the shape expand the region generating lift up to the rear of the configuration. Also, the tendency of the pitching moment with both Mach number and angle of attack was analyzed by comparing the positions of the center of pressure and the center of gravity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.6
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• pp.445-451
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• 2018

This paper describes on introduction of CASE 4(Delta Wing) for EFD-CFD comparison workshop which is in charged of aerodynamic subcommittee of The Korean Society for Aeronautical and Space Science. The wind tunnel test will be performed later, angle of attack is set -5~20deg and mach number is set 0.7, 0.85, 1.2 to solve the transonic flow. The simulation test of grid dependency is conducted to determine the proper grid size of delta wing analysis. The tendency of lift and drag coefficient is determined according to the change of angle of attack based on the selected grid size.