Reynolds-averaged Navier-Stokes Analysis Research Articles

대리모델들을 이용한 인쇄형 열교환기의 최적설계

Shape optimization of a Printed circuit heat exchanger (PCHE) has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (3-D RANS) analysis and surrogate modeling techniques. The objective function is defined as a linear combination of effectiveness of the PCHE term and pressure drop in the cold channels of the PCHE. The cold channel angle and the ellipse aspect ratio of the cold channel are used as design variables for the optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results of three types of surrogate model are compared each other. The results of the optimizations indicate improved performance in friction loss but low performance in effectiveness than the reference shape.

Multiobjective Design Optimization of the Upper Plenum of a PBMR-Type Gas-Cooled Nuclear Reactor

The shape optimization of the upper plenum of a pebble bed modular reactor (PBMR)-type gas-cooled nuclear reactor has been performed by using three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis and a multiobjective optimization procedure. A multiobjective genetic algorithm is used for multiobjective optimization. Two objective functions related to the uniformity of the flow distribution at the core inlet and pressure drop through the upper plenum are employed. Three geometric design variables, namely, the ratio of the thickness of the slot to the diameter of the rising channels, the ratio of the height of the upper plenum to the diameter of the rising channels, and the ratio of the height of the slot at the inlet to that at the outlet, are used for the optimization. Latin hypercube sampling is used to determine the experimental points. The response surface approximation model is used to approximate the Pareto-optimal front with three-dimensional RANS analysis using the shear stress transport turbulence model. Seven optimal shapes have been obtained using k-means clustering. From an analysis of two typical optimal designs, it is found that both of the objective functions have been improved remarkably in comparison with the reference design.

Multi-objective optimization of a cooling channel with staggered elliptic dimples

The present work deals with a numerical procedure for optimizing a cooling channel with staggered elliptic dimples to enhance heat transfer and also to reduce the pressure loss. Three-dimensional Reynolds-averaged Navier–Stokes analysis is employed in conjunction with the SST model for predicting the turbulent flow and heat transfer. Three non-dimensional geometric design variables, such as the elliptic dimple diameter ratio, ratio of the dimple depth to average diameter, and ratio of the streamwise distance to spanwise distance between dimples are considered for the optimization. Twenty-one design points within the design space are selected by Latin hypercube sampling. Each objective-function value at these points is evaluated by RANS analysis to construct a surrogate model using the Kriging approach. A hybrid evolutionary multi-objective algorithm has been employed to find optimized designs considering the heat transfer and friction loss. Two extreme optimum designs on the Pareto-optimal front with regard to the heat transfer and pressure loss, respectively, have spanwise and streamwise elliptic dimple shapes, respectively, which increase the heat-transfer rate by 32.8% and decrease the pressure loss by 34.6%, respectively, compared to the reference design.

회전하는 냉각유로의 곡관부에 부착된 가이드 베인의 형상 최적설계

The heat transfer and pressure loss characteristics of a rotating two-pass channel with a guide vane in the turning region have been studied using three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis, and the shape of the guide vane has been optimized using surrogate modeling optimization technique. For the optimization, thickness, location and angle of the guide vanes have been selected as design variables. The objective function has been defined as a linear combination of the heat transfer and the friction loss related terms with a weighting factor. Latin hypercube sampling has been applied to determine the design points as design of experiments. A weighted-average surrogate model, PBA has been used as the surrogate model. The guide vane in the turning region does not influence the heat transfer in the first passage upstream of the turning region, but enhances largely the heat transfer in the turning region and the second passage. In an example of the optimization, the objective function has been increased by 13.6%.

Modeling Synthetic Jets for Low-Re Airfoil Unsteady Flow Control

Synthetic jet actuators (SJAs) may be carefully designed to alleviate the negative impact of impinging flow non-uniformities on the aircraft wing unsteady aerodynamic response. The current study investigates the effectiveness of SJAs for active control of unsteady flow over SD7003 low-Re airfoil in presence of a high-amplitude upstream flow disturbance characterized by a sharp-edge gust. In the adopted numerical procedure, the actuator's dimensional scaling and excitation frequency effects are first examined for a specific SJA configuration using a Lumped Element Model. The next step employs a Reynolds-averaged Navier-Stokes analysis to determine simple fluctuating-velocity boundary condition at the bottom of the actuator's orifice. The orifice with the properly defined boundary condition is then embedded into the airfoil surface for conducting high-accuracy viscous analysis of active flow control during gust-airfoil interaction process. Results of numerical simulations indicate that the SJA positive effe...

Combining Computational Fluid Dynamics Analysis Data with Experimentally Measured Data

ABSTRACT This article presents an approach to reducing the time and cost of experimentation in large wind tunnels, such as the 10 × 10 ft. supersonic wind tunnel at NASA Glenn Research Center, by combining computer simulations of test models from Reynolds averaged Navier-Stokes analysis with small sets of wind tunnel data. To demonstrate the viability of the approach, the impact of microramp flow control on the shock wave boundary layer interaction using paired sets of data from both computational fluid dynamics (CFD) analysis and experimental measurements was compared. By combining the CFD results consisting of 15 central composite face-centered (CCF) simulations with a smaller subset of four/five experimental wind tunnel cases, augmented, interlocking combined data sets were generated from which models were developed that allow the prediction of wind tunnel results. No statistically significant differences were found to exist between the predictions from models generated using the augmented interlocking data sets and the models generated using the complete set of 15 wind tunnel cases based on a paired t-test. From an engineering perspective, the same optimal microramp configuration was obtained using models derived from the combined data set as obtained with the complete set of experimental wind tunnel data.

신경회로망기법을 사용한 타원형 딤플유로의 냉각성능 최적화

The present analysis deals with a numerical procedure for optimizing the shape of elliptical dimples in a cooling channel. The three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis is employed in conjunction with the SST model for predictions of the turbulent flow and the heat transfer. Three non-dimensional geometric design variables, such as the ellipse dimple diameter ratio, ratio of the dimple depth to the average diameter, and ratio of the distance between dimples to the pitch are considered in the optimization. Twenty-one experimental points within design space are selected by Latin Hypercube Sampling. Each objective function values at these points are evaluated by RANS analysis and producing optimal point using surrogate model. The linear combination of heat transfer coefficient and friction loss related terms with a weighting factor is defined as the objective function. The results show that the optimized elliptical dimple shape improves considerably the heat transfer performance than the circular dimple shape.

Shape Optimization of a Dimpled Channel to Enhance Heat Transfer Using a Weighted-Average Surrogate Model

Shape optimization of a rectangular channel with the opposite walls roughened by staggered arrays of dimples has been performed not only to enhance turbulent heat transfer but also to reduce friction loss. The dimpled channel shape is defined by three geometric design variables, and the design points within design space are selected using Latin hypercube sampling. The shape of the channel is optimized with three-dimensional (3-D) Reynolds-averaged Navier–Stokes analysis and surrogate approximation methods. A weighted-sum method for multi-objective optimization is applied to integrate multiple objectives related to heat transfer and friction loss into a single objective. A weighted-average surrogate model is employed for this optimization. By the optimization, the objective function value is improved largely and heat transfer rate is increased much higher than pressure loss increase due to shape deformation. The optimum design results in lower channel height, wider dimple spacing, and deeper dimple. The flow mechanism shows the heat transfer rate is increased mainly in the rear portion of the dimple.

곡관부 하류에 핀휜이 부착된 회전 냉각유로의 최적설계

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

Surrogate based optimization of a laidback fan-shaped hole for film-cooling

The present work has been performed to evaluate the effects of geometric variables of a laidback fan-shaped hole on the film-cooling effectiveness using a Reynolds-averaged Navier–Stokes analysis, and to optimize the shape of the hole using the Kriging meta-modeling technique. The shape of the laidback fan-shaped hole is defined by four geometric design variables, namely, the injection angle of the hole, the lateral expansion angle of the diffuser, the forward expansion angle of the hole, and the ratio of the length to the diameter of the hole. From the results of a parametric study, effects of design variables on the film-cooling effectiveness are evaluated. The objective function, which is defined as the spatially averaged film-cooling effectiveness, is numerically evaluated through a RANS analysis at design points selected through Latin hypercube sampling. The Kriging model is used to approximate these objective function values at the design points, and sequential quadratic programming is used to search for the optimal point from the constructed Kriging model. The optimizations are carried out for two different blowing ratios, 0.5 and 2.5. The film-cooling effectiveness has been successfully improved with the optimization as compared to the reference geometry.

Propeller Empennage Interaction Effects on the Vertical Tail Design of Multiengine Aircraft

A potential-flow model for conceptual design and vertical tail sizing purposes, currently under development, has been applied and tested in an investigation of the influence of the propeller slipstream on the empennage flowfield. Additionally, the model is intended to increase the understanding of the phenomena arising in propeller-empennage interaction. For verification purposes and complementation to limited wind-tunnel results in open literature, dedicated measurements were performed and supplemented by a Reynolds-averaged Navier-Stokes analysis. From wind-tunnel measurements, in one-engine-inoperative condition, it is found that the empennage experiences a propeller-induced crossflowfield, which is found to be the main contributor to the additional yawing moment experienced by the measured multiengine propeller aircraft. The most probable cause for deviation in yawing moments in measurements and the potential-flow model is incorrect modeling of the flowfield behind the wing. This was verified by a comparison of the measured and computed flowfield behind the wing and in front of the vertical tail. Efforts to create a potential model to aid in conceptual vertical tail sizing should, therefore, focus on achieving realistic wing-wake behavior. In this respect, the effect of the propeller on the wing-lift distribution, as well as the wing-wake aircraft interaction, should be treated with care.

핀휜이 부착된 회전하는 냉각유로의 최적설계

본 연구에서는 크리깅 기법을 이용하여 엇갈린 핀휜이 부착된 회전하는 내부냉각유로의 형상 최적화를 수행하였다. 냉각유로 형상의 여러 매개변수 중 핀의 지름과 높이의 비, 핀의 지름과 핀과 핀 사이의 거리의 비를 최적설계를 위한 설계변수로 선택하였다. 열전달 관련 목적함수와 마찰손실 관련 목적함수를 가중계수를 이용하여 선형적으로 결합한 목적함수를 정의하였다. 크리깅 모델을 구축하기 위해 라틴하이퍼큐브 샘플링기법에 의해 생성된 20개 실험점에서 목적함수가 SST난류모델을 사용한 삼차원 레이놀즈평균 나비어-스톡스(RANS) 유동해석법에 의해 계산되었다. 크리깅 기법을 통하여 예측된 목적함수값은 RANS해석을 이용해 계산된 값과 매우 작은 오차 범위 내에서 일치하였으며, 최적설계를 통해 목적함수가 11% 감소하는 결과를 얻었다.

Multi-objective optimization of a centrifugal compressor impeller through evolutionary algorithms

This paper presents the design optimization of a centrifugal compressor impeller with a hybrid multi-objective evolutionary algorithm. Reynolds-averaged Navier—Stokes (RANS) equations are solved with the shear stress transport turbulence model as a turbulence closure model. Flow analysis is performed on a hexahedral grid through a finite-volume solver. Two objectives, viz., the isentropic efficiency and the total pressure ratio (PR), are selected with four design variables that define the impeller hub and shroud contours in meridian terms for optimizing the system. The validation of numerical results was performed through experimental data for the total PR and the isentropic efficiency. Objective-function values are numerically evaluated through the RANS analysis at design points that are selected through the Latin hypercube sampling method. A fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with an ε-constraint strategy for local search coupled with a surrogate model is used for multi-objective optimization. The surrogate model, the radial basis neural network, is trained on discrete numerical solutions by the execution of leave-one-out cross-validation for the dataset. The trade-off between the two objectives has been ascertained and discussed in the light of Pareto-optimal solutions. The optimization results show that the isentropic efficiency and the total PR are enhanced at both design and off-design conditions through multi-objective optimization.

Shape optimization of a fan-shaped hole to enhance film-cooling effectiveness

A fan-shaped hole for film cooling has been studied to find the effect of geometric variations on the cooling performance and optimized to enhance film-cooling effectiveness using three-dimensional Reynolds-averaged Navier–Stokes analysis and surrogate approximation methods. The computational results for film-cooling effectiveness using SST turbulence model have been validated in comparison with the experimental data. The injection angle, lateral expansion angle, and ratio of length-to-diameter of the hole are chosen as the design variables, and the effects of these variables on the cooling performance are evaluated. To optimize a fan-shaped hole, the spatially-averaged film-cooling effectiveness is considered as the objective function, which is to be maximized. Latin hypercube sampling is used to determine the training points as a means of the design of experiment. A weighted-average surrogate model is used to approximate the data generated by numerical analysis at the design points. And, sequential quadratic programming is used to search for the optimal point from the constructed surrogate. The results of the optimization show that the film-cooling effectiveness has been successfully improved through optimization, when compared with the reference geometry.

Heat Transfer and Friction Characteristics Optimization with Compound Turbulators in Roughened Ducts

AbstractThe use of artificial roughness or turbulence promoters on a surface is an effective technique to enhance the rate of heat transfer of the fluid flowing in a duct. In this study, a computer code has been developed to perform a numerical simulation for optimizing the shape of two-dimensional channel with periodic ribs mounted on the bottom wall to enhance turbulent heat transfer. The Reynolds-Averaged Navier-Stokes analysis is used as a numerical technique and the SST k-(ω) turbulent model with near-wall treatment as a turbulent model. The simulations were performed for two rib shapes, trapezoidal with decreasing height in the flow direction with and without grooves between the ribs. The results are validated by comparing with existing experimental data and semi-empirical correlations. The Reynolds number, pitch-to-rib high ratio and relative groove position are chosen as design variables. The effects of roughness parameters on Nusselt number and friction factor have been discussed and the conditions for the best performance have been determined and presented.

홴형상 막냉각홀의 신경회로망 기법을 이용한 최적설계

Numerical design optimization of a fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness by combining a three-dimensional Reynolds-averaged Navier-Stokes analysis with the radial basis neural network method, a well known surrogate modeling technique for optimization. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. Twenty training points are obtained by Latin Hypercube sampling for three design variables. Sequential quadratic programming is used to search for the optimal point from the constructed surrogate. The film-cooling effectiveness has been successfully improved by the optimization with increased value of all design variables as compared to the reference geometry.

핵연료 봉다발내 비틀린 혼합날개의 형상최적설계

The purposes of present work are to analyze the convective heat transfer with three-dimensional Reynolds-averaged Navier-Stokes analysis, and to optimize shape of the mixing vane using the analysis results. Response surface method is employed as an optimization technique. The objective function is defined as a combination of inverse of heat transfer rate and friction loss. Two bend angles of mixing vane are selected as design variables. Thermal-hydraulic performances have been discussed and optimum shape has been obtained as a function of weighting factor in the objective function. The results show that the optimized geometry improves the heat transfer performance far downstream of the mixing vane.

Shape Optimization of Inlet Plenum in a PBMR-Type Gas-Cooled Nuclear Reactor

The pebble-bed modular reactor (PBMR) as a high-temperature gas-cooled reactor is one of the renewed reactor designs of generation IV. In this work, the shape optimization of the inlet plenum and rising channels in PMBR has been performed based on three dimensional Reynolds-averaged Navier-Stokes analysis. The objectives of the design are to maximize the uniformity in the flow distribution in rising channels and to minimize the pressure drop

Optimization of a Cylindrical Film Cooling Hole using Surrogate Modeling

Optimization of a cylindrical film-cooling hole has been performed by surrogate modeling approach using three-dimensional Reynolds-averaged Navier-Stokes analysis. SST model has been employed as a turbulence closure model for the analysis of turbulent convective heat transfer. Spatially-averaged film-cooling effectiveness has been maximized for optimization. For two design variables, the ratio of length to the diameter of the hole and ejection angle, 12 experimental points are selected by Latin hypercube sampling. Performances of three basic surrogate models and three weighted average surrogate models have been evaluated. Among the surrogate models tested, the Kriging model predicts the optimum point with the highest objective function value calculated by Reynolds-averaged Navier-Stokes analysis, which gives a 3.6% improvement of the spatially-averaged film-cooling effectiveness in comparison to the reference geometry. The objective function is more sensitive to the ejection angle than the ratio of length to diameter of the hole.

Shape Optimization of 19-Pin Wire-Wrapped Fuel Assembly of LMR Using Multiobjective Evolutionary Algorithm

In this work multiobjective shape optimization of a 19-pin wire-wrapped fuel assembly is carried out using a hybrid multiobjective evolutionary approach in order to achieve an acceptable compromise between two competing objectives, i.e., enhancement of heat transfer and reduction of friction loss. Two nondimensional variables, wire-spacer diameter to fuel rod diameter ratio and wire-wrap pitch to fuel rod diameter ratio, are chosen as design variables. The response surface approximation method is used to construct the surrogate with objective function values calculated by means of Reynolds-averaged Navier-Stokes analysis of the flow and heat transfer. The shear stress transport turbulence model is used as a turbulence closure. The optimization results are processed by the Pareto-optimal method. The Pareto-optimal solutions are obtained using a combination of the evolutionary algorithm NSGA-II and a local search method. The Pareto-optimal front for the wire-wrapped fuel assembly has been obtained. With an increase in the wire-spacer diameter, both heat transfer and friction loss in the assembly increase. The design with higher heat transfer on the Pareto-optimal curve shows not only a lower maximum temperature but also a more uniform temperature distribution on the cross section of the assembly in comparison with the other designs.