크리깅 방법에 의한 방열판 최적설계

*† ‡ § An efficient and high-fidelity design approach is proposed by combining global and local optimization methods for wing planform and surface design. For enhanced design results, aerodynamic shape optimization process is carried out via 2-stage with different optimization strategy. In the first stage, global optimization techniques are applied to planform design with a few geometric design variables. In the second stage, local optimization techniques are used for wing surface design with a lot of design variables to maintain a sufficient design space with high DOF (Degree of Freedom) geometric change. For global optimization, meta-modeling techniques such as RS (Response Surface) and Kriging methods are used in conjunction with Genetic Algorithm (GA). For local optimization, a discrete adjoint variable method is used. By the successive combination of global and local optimization techniques, drag minimization is performed for a multi-body aircraft configuration while maintaining the baseline lift and the wing weight at the same time. Through the design process, performances of the test models are remarkably improved in comparison with the single stage design approach. The capability of proposed design framework including wing planform design variables can be evaluated by the drag decomposition method which can provide improvement of induced drag and wave drag, respectively.

Optimization of thermal design of ribbed flat-plate fin heat sink

Design optimization of plate-fin heat sink with forced convection for single-module thermoelectric generator

This work presents a simplified approach to optimally designing a heat sink with metallic thermal conductivity enhancers infiltrated with phase change material for electronic cooling. In present study, thermal conductivity enhancers are in the form of a honeycomb structure. A benchmarked two-dimensional computational fluid dynamics model was employed to investigate the thermal performance of the phase change material-metallic thermal conductivity enhancer composite heat sinks. Metallic thermal conductivity enhancers are often used in conjunction with phase change material to enhance the conductivity of the composite heat sink. Under constrained heat sink volume, the higher volume fraction of thermal conductivity enhancers improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of heat sink for electronic cooling by resolving the stated tradeoff. In this study, the total volume of the heat sink and the interfacial heat transfer area between the phase change material and thermal conductivity enhancers are constrained for all design points. Furthermore, assuming conduction-dominated heat transfer, an effective numerical model that solves the single energy equation with the effective properties of the phase change material- metallic thermal conductivity enhancer composite has been developed. The temperature gradient-time history is compared and matched for both the models to arrive at the accurate effective thermal conductivity value. The relationship of effective thermal conductivity as a function of metal volume fraction and thermal conductivity of metallic thermal conductivity enhancer is obtained. The figure of merit (FOM) is used to define the balance between effective thermal conductivity and energy storage capacity. The FOM is maximized to find the optimal volume fraction for the present design. The results from the study reveals that there exists an optimal metal volume fraction that maximizes the thermal performance of the composite.

This paper discusses the use of the second law in heat sink design. A new entropy-based cost function is proposed and compared with existing heat sink cost functions. A case study of a plate fin heat sink points out that this newly developed cost function offers a heat sink which is more than twice as efficient as a heat sink designed with the traditional thermal resistance minimization objective. The effects of this new heat sink design on data center cooling systems are considered and found to be significantly improving the system efficiency and waste heat recovery.

Battery thermal management has significant effect on the performance of electric vehicles (EVs) under high current rates. In this research, a comprehensive thermal analysis and multi-objective optimization design framework is proposed to enhance the thermal performance of a novel air–liquid cooling coupled battery pack under higher discharging rate (3C). Computational fluid dynamics (CFD) numerical calculation is utilized to compare the cooling efficiency of the battery pack designs. Furthermore, a surrogate model is generated by using Latin hypercube sampling (LHS) and support vector machine. The design parameters include different mini-channels’ mass flowrates and the air flow inlet velocity, the objectives are the temperature rise, temperature distribution, and the energy consumption. Sensitivity analysis results indicate that the air flow inlet velocity is the main factor affecting the temperature rise and temperature distribution, while the mass flowrates of mini-channels have important influence on the pressure drop. Finally, the nondominated sorting genetic algorithm-II (NSGA-II) is used to select the optimal battery pack design, the maximum temperature, and temperature standard deviation (TSD) get improved by 1.8 K and 0.06 K, respectively. And the energy consumption of the cooling system can be controlled within the appropriate range after optimization design.

Modeling arrays of passive vortex generators (VGs) pairs, mounted in the fully turbulent boundary layer of a flat plate and generating streamwise counterrotating vortex structures is the object of this investigation. Usually, a sound computational fluid dynamics (CFD) investigation requires an adequate grid with a corresponding large number of grid points around such VGs in order to obtain an accurate solution of this flow case. This, in turn, leads to a time-demanding grid generation which often comes along with lots of practical challenges during the creation. An effective way to get around this time-consuming process is to introduce a way to model these flow separation devices statistically and, by that, to add their statistical physical effects to the governing equations rather than resolving their geometries in the computational grid. KTH, the Royal Institute of Technology Stockholm, and FOI, the Swedish Defence Research Agency, have developed a computational tool for statistical VG modeling that makes it possible to simulate and add the additional statistical effects of passive VGs in wall-bounded flows, whereas the need for a local mesh refinement is no longer required. This approach for the modeling of passive VGs turbulent flow separation devices is presented using a two dimensional Navier-Stokes flow solver. Computational results for fully three dimensional resolved VGs as well as experimental results are evaluated and compared to this statistical VG model approach. It is shown that the VG model approach gives very promising results that compare well to results from CFD and experiments. Nevertheless, the influence of the vortex structures on the flow and on the turbulent stresses decays quicker than it is observed in experiments. Further-more, the statistical VG model is evaluated for asymmetric diffuser flow and compared to experimental data with as well as without VGs. It is shown that the VG model is capable of predicting the influence of the VGs on decreased and vanished separation of this highly sensitive flow case, giving a better pressure recovery at the diffuser's outlet.

The design of rigid vortex generators (RVG) influences the thermal performance of various technologies. We employed Discrete Adjoint-Based Optimization to show the optimal development of vortex generators. Under turbulent flow conditions, different bi-objective functions on the RVG design were examined. Specifically, we aimed at an optimal RVG shape that minimizes the pressure drop and maximizes the local heat transfer in a rectangular channel. We show that an optimal design of an RVG can be obtained using computational fluid dynamics in conjunction with the Pareto Front at a computational cost of the order ~O(10^{-1}). We obtained three essential vortex generator shapes based on the RVG morphing technique. Compared to the baseline geometry of a delta winglet pair DWP, the first morphed design reduced the pressure drop by 39%, however, at the expense of a 21% reduction in the Nusselt number. The second vortex generator design enhanced the heat transfer by 18%, however, at the cost of a significant increase in pressure drop of about 40%. The final morphed design achieved the highest thermal performance factor of 1.28, representing a heat transfer enhancement of 6% with a moderate increase in pressure drop of about 13% compared to DWP vortex generators. Furthermore, we investigated the effect of introducing different size holes on the mass reduction of vortex generators and their thermal performances. The mass of vortex generators can be reduced by 9% and with an increase of 7% in thermal performance factor concerning the DWP baseline. The findings of this study will lead to highly efficient lightweight heat exchangers.

A surrogate model based aerodynamic shape optimization method applied to the wind deflector of a tractor-trailer in crosswind is presented in this paper. The aerodynamic drag coefficient and handling stability of the tractor-trailer subjected to crosswinds is analyzed. The numerical results show that the wind deflector can influence drag coefficient and the lateral displacement of the tractor-trailer in crosswinds in great degree. Four parameters are used to describe the wind deflector geometry: Width, Length, Height and Angle. A 30-level design of experiments (DOE) study using the optimal Latin hypercube method is conducted to analyze the sensitivity of the design variables and build a database to set up the surrogate model. The surrogate model is constructed based on the Kriging interpolation technique. The fitting precision of the surrogate model is examined using a computational fluid dynamics (CFD) and multi-body dynamics and certified using a surrogate model simulation. Finally, multi-island genetic algorithm is used to optimize the shape of the wind deflector based on the surrogate model. The maximum tolerance between the results of the CFD and multi-body dynamics simulation and the surrogate model is only 2.02 %. When using the optimal design variables, the aerodynamics drag coefficient decreases maximum by 6.23 % and the lateral displacement decreases maximum by 4.67 %.KeywordsMultidisciplinary optimizationVehicle aerodynamicsMulti-body dynamicsCrosswind

Effects of applying uniform and non-uniform external magnetic fields on the optimal design of microchannel heat sinks

Bi-leaflet Mechanical Heart Valve (BMHV) is widely used in surgically heart valve replacement in worldwide. The main complication of the BMHV is that BMHV leaded to the formation of blood clotting known as thrombosis. Vortex Generator (VG) is used to improve the performance of the BMHV by delaying the turbulence that activated the platelet and hemolysis. This paper presents various configuration of VG to enhance the performance of BMHV. In this Computational Fluid Dynamic (CFD) approach, a simplified prosthetic heart valve is used to investigate the performance of BMHV with different orientation of VG. As a result, the fluid is passed through the leaflets with VG. The pressure drop is decreased between the position of after leaflets and before leaflets. In the present study, four different configurations of VG are reviewed, which are without VG, Co-counter Equally Spaced VG, Straight Equally Spaced VG and Counter-rotating Far Spaced VG. In the other hand, this present study also investigates the pulsatile turbulent transient flow in simplified prosthetic heart valve with no VG and the best configuration of VG in the previous study. In the present study, Co-counter Equally Spaced VG is the best configuration and it contributed 42.62% of improvement in pressure drop across the leaflets. Besides that, Co-counter Equally Spaced provided 52.96% and 7.82% reduction in Turbulence Shear Stress and Turbulence Kinetic Energy respectively. In the summary, the pressure drop, turbulence kinetic energy and turbulence shear stress are significantly reduced due to the existence of VG. VG is a crucial device to enhance the performance of BMHV by delaying early separation and thus turbulence reduced.

A finite element/boundary element design tool is used to perform a structural acoustic optimization on an eight-ply graphite epoxy cylindrical shell. The shell is subject to two external monopole sources vibrating at a single frequency. The goal of the optimization is the minimization of the sum of the squared pressure amplitudes within the enclosed acoustic cavity. The ply angles serve as the design variables in optimization. The optimal design was obtained after 15 iterations with a 2 dB reduction in the average interior sound pressure level. The ply angle orientation shifted from an initially symmetric lay-up to an unsymmetric lay-up in the final design.

Material optimization of tri-directional functionally graded plates by using deep neural network and isogeometric multimesh design approach

Counter-rotating vortex generators (VGs) are typically employed to delay airflow separation on wind turbine blades. Large-size wind turbine blades equipped with small size VGs make the computational fluid dynamics (CFD) researches require a great deal of computational resources. Parametric models of VGs can effectively improve the numerical research efficiency of wind turbine blades with VGs. In order to improve the accuracy of such parametric models, this study proposed a series of modeling approaches to determine the positions of the adding source term in Cartesian coordinates, the VG vortex core radius, etc., on the wind turbine airfoils. These techniques are integrated with a maximum circulation algorithm by considering the interactions between VG pairs to predict the performance of a DU91-W2-250 blade section with VGs. The proposed parametric model and an entity model at different angles of attack (AoAs) are implemented on the blade section. Our approach is validated using experimental data. Comparisons demonstrate a strong agreement between the modelled and experimental results, proving the high accuracy of the two models. The numerical results of the models are then compared and analyzed at different incoming flow velocities and AoAs to verify the universality of the proposed parametric approaches. The results reveal a high consistency between the vortex structure, the velocity profile above the blade surface and the distribution of the pressure coefficient calculated by the two models. This proves the high universality of the proposed approaches and demonstrates the potential of the parametric model in replacing the VG entity model. The VG parametric model expresses VG parameters by program, which can improve the research efficiency of VG arrangement on wind turbine blades.

Many researchers have studied the thermal performance of heat sinks, however to the best knowledge of the authors, the effect of flow direction (place of fan) on the thermal performance of plate-fin heat sinks with fillet profile have not yet been investigated. In this paper, the investigation develops a computational fluid dynamics (CFD) model, validated through comparison with an experimental data from the literature, which demonstrates the effect of flow direction and fillet profile on the thermal performance of plate-fin heat sinks. In particular, a plate-fin heat sink with fillet profile subject to parallel flow has been compared with the conventional design (plate-fin heat sink without fillet profile subject to an impinging flow) and satisfactory results have been perceived. The results of this study show that the base temperature along with the thermal resistance of the heat sink is lower for the proposed design. Therefore, the developed approach has strong potential to be used to improve the thermal performance of heat sinks and hence to develop more advanced effective cooling technologies.