FEA/CFD Analysis for Fluid-Structure Interaction Studies

Key Takeaways

• FEA/CFD analysis is an advanced, computerized analysis technique used to identify problems in design due to various internal and external conditions or forces. 

• In coupled FEA/CFD analysis, there can be CFD boundary domains within the FEA model. The CFD domains may either partially or completely cover the FEA model boundary. This analysis couples the neighboring FEA/CFD boundaries; the rest, which are not coupled, follow conventional thermal boundary conditions.

• In the FEA/CFD analysis of heat exchangers, important design parameters to consider include costs, liquid coolant flow rate, cooling performance, mechanical strength, and pressure drop.

FEA computer simulation

For the optimum operation of electronic systems, smart product design is required to handle challenges set by working conditions and environment. In electronic product design, the interaction between fluid and structure must be analyzed, with considerations for market competition on cost optimization, miniaturization, and integrated features within a reliable assembly. 

The rapid growth of wireless technologies has increased the demand for product downsizing and long battery life, which requires careful fluid-structure interaction analysis. Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) analysis, known collectively as FEA/CFD analysis, is an advanced, computerized analysis technique used to identify problems in design due to various internal and external conditions or forces. 

FEA determines the effects of stress, vibrations, fatigue, and heat, predicting problem areas in a design before failure occurs. CFD analysis focuses on the interaction between fluid-fluid, fluid-gas, or fluid-solids. When coupled together, FEA/CFD analysis provides information corresponding to each analysis and ensures all aspects of a design are approved.

Approaches to FEA /CFD Analysis

In FEA/CFD analysis, FEA and CFD analysis are conducted with separate codes, but relevant information is shared between the codes to ensure the continuity of temperature and heat flux across the coupled boundaries between the FEA and CFD models. There are various approaches in FEA/CFD analysis such as 2D FEA/2D CFD coupling, 2D FEA/3D CFD, and 3D FEA/3D CFD. All of these approaches provide the benefits of both FEA and CFD analysis.

Boundaries in FEA/CFD Analysis

In coupled FEA/CFD analysis, there can be CFD boundary domains within the FEA model. The CFD domains may either partially or completely cover the FEA model boundary. This analysis couples the neighboring FEA/CFD boundaries. The rest of the boundaries, which are not coupled, follow conventional thermal boundary conditions.

In coupled FEA/CFD analysis, the continuity of heat flux and temperature across coupled boundaries is confirmed by iterative loops between FEA and CFD simulations. The convergence of thermal coupling iterations is recognized from the difference of coupled wall temperatures from two consecutive iterations. If the difference is within the tolerance range, then convergence is achieved. 

Boundary conditions of non-coupled walls are dynamically updated in coupled FEA/CFD analysis, and the intermediate FEA and CFD solutions obtained correspond with each update. On the coupling walls, temperature distributions obtained from FEA simulations and heat flux distributions from CFD simulations are used to define the temperature boundary condition for the CFD model and the heat flux boundary condition for the FEA model.

Now, we will examine an example application of FEA/CFD analysis as it relates to power devices in electric vehicles.

Pin-Fin Heat Sink Design for Electric Vehicle Power Modules

In electric vehicles, several power devices are used as heat-generating sources.  Optimizing these designs—both the weight and size of the heat exchanger—is essential to reducing the weight of the powering systems in electric vehicles. 

Power modules in electric vehicles are usually liquid-cooled using a cold plate. This liquid cooling can be modeled, simulated, and analyzed using coupled FEA/CFD analysis. Both the FEA model and the CFD model of the heat exchanger focuses on the heat transfer and the fluid flow in it. The accuracy of the simulation results depends on the fineness of the mesh near the structure-fluid interfaces and across the flow channels. However, the finer the mesh, the higher the computational time and memory requirements. 

FEA/CFD Analysis of Heat Exchangers

In the FEA/CFD analysis of heat exchangers, important design parameters to consider include costs, liquid coolant flow rate, cooling performance, mechanical strength, and pressure drop. 

Pin fin-type heat sinks are used on power electronic systems in electric vehicles due to their relatively low-pressure drop and heat transfer efficiency. By using an FEA/CFD simulation, engineers can find the pin-fin to rear channel ratio, the pin-fin geometry, and the arrangement that would provide the most optimized heat sink design with the highest cooling performance and lowest pressure drop. 

From FEA/CFD simulations, we can see the predicted temperature profile for each geometry of pin fins, such as diamond-shaped, elliptical-shaped, or rectangular-shaped, the corresponding peak temperature and pressure drops, and can choose the best-suited design based on the numerical values and temperature profile. 

In engineering designs, flow and heat transfer processes threaten the life of a product or structure. Using simulation and computer analysis—rather than prototyping—is recommended to predict the potential risk areas in a design. FEA/CFD analysis is the best tool for modeling, simulating, and analyzing the fluid-structure interactions in a design. To optimize the performance, reliability, and safety of a product, consider using FEA/CFD analysis.