By Grey Lerner, Mechanical Engineer
Determining the flow state of fluids is required in order to solve many types of engineering problems. Gases and liquids, both considered fluids, are used for many purposes including system temperature control, media transport, atmospheric control, and automation. Ascertaining how fluids will flow through a system can be critical to its operation. A fluid’s flow state can be determined analytically, experimentally, numerically, and by using computational fluid dynamics (CFD) to verify it will meet the needs of the system. SIGMADESIGN engineers analyze fluid flow throughout the design process using computational fluid dynamics in order to reduce project time and cost for clients.
FINDING THE RIGHT ANALYSIS TOOL
Analytical solutions to flow problems suffice in many situations where the problem can be adequately simplified. However, after simplification, these solutions may not accurately describe the problem being posed. Numerical and experimental methods can be utilized when problems are too complex for analytical methods. Experimental flow analysis methods are generally time consuming and labor intensive. When several variables are to be determined, conducting experiments can become intractable in the product development environment.
CFD utilizes numerical analysis and data structures to determine solutions for a variety of types of problems. Using SOLIDWORKS Flow Simulation, SIGMADESIGN’s engineering team studies how fluids behave to provide meaningful insight into the impact of fluid flow. By applying CFD studies on projects, problems are addressed early and, as a result, prototype costs and costly reworks are reduced.
UNDERSTANDING WHEN TO USE CFD
CFD allows for physical systems to be modeled, solved, and iterated upon more expeditiously and frugally. Therefore, fewer physical prototypes are required to verify the solutions, which can decrease overhead and reduce timelines. Static, transient, linear, and non-linear problems can be solved.
So, what project specific questions can you answer through the use of CFD? Examples include:
- Will the components on my printed circuit board (PCB) overheat?
- What size pump is required to meet the flowrate and pressure requirements?
- Should a blower or axial fan be utilized in the design?
- What piping diameters are required to balance fluid flow through a multi-path manifold?
- Is natural or forced convection required to transfer the required thermal energy?
- What is the force imparted on objects due to fluid flow?
HOW CFD MODELS ARE USED IN A PROJECT
CFD models can be very useful early in the design phase of a project. Engineering challenges begin with a need or problem statement. Project specifications are identified to meet this need and analytical solutions for the simplified problem are developed. Then, you are able to build models, identify fluid flow problems, and solve issues at an early stage in the design process. We share these models with our clients so they can understand if their system is working as they intend.
CAD models are pre-processed (usually simplified), making them suitable for numerical simulation. The models are discretized, or meshed, by the software. Boundary conditions, initial conditions, and material properties are defined. The differential equations governing fluid flow (The Navier-Stokes equation) are solved in an iterative process across the discretized mesh. In this way, the model is solved and the results are post-processed and studied. Results from the numerical analysis are compared against any available analytical or experimental results. As necessary, we refine the model and solution to meet the project specifications. As the design moves forward, physical prototypes are built and the CFD models inform the physical their design. By using CFD, we can mitigate development timelines and costs.
The two case studies below illustrate how CFD can be used in a project.
Case Study: Electronics Enclosure
One of our clients needed to place electronics in an enclosure with limited airflow. To determine the best placement for the electronics, SIGMADESIGN used CFD to visualize the airflow and cooling potential. Electronics that produce more heat or are more sensitive to temperature can be placed in areas with greater airflow. Dark blue arrows show areas with slower moving air, while green arrows show areas with faster moving air; areas with a greater cooling potential. By using CFD to analyze airflow, we are able to avoid risks to a project’s function and reduce costs for our clients.
Case Study: Water-cooled power supply plumbing
Another client of ours required coolant to be provided through a manifold to several power supplies. Sufficient flow to each of the devices was required, and CFD aided in designing plumbing that met their needs.
The devices’ flow requirements varied, and it was necessary to provide adequate coolant to each of them. Implementing adjustable flow controls and gauges at each leg was deemed both too expensive and too bulky. Instead, different sized orifices were placed in the manifold’s legs to balance the flow. Calculating the sizes of the orifices was done analytically and verified with CFD.
The image below shows the portion of the system containing the supplies and plumbing. One leg of the plumbing manifold is shown along with a couple of different result displays. Once developed, multiple scenarios were set up and solved on the basic model. Both the system’s input flow specifications, and the individual device’s flow parameters were subject to variation.
The CFD model was very helpful in quickly providing results across the range of variables. The graphical output is useful in comparing multiple results efficiently and they can be queried for the numerical results as well. These results are often animated, which further aids in understanding their content. By using CFD, SIGMADESIGN engineers are able to analyze complex problems and develop solutions that help reduce project time and cost for our clients.