Finite element modeling of fluid flow using COMSOL multiphysics

Manivannan, Sanjayan

Student Work

Finite element modeling of fluid flow using COMSOL multiphysics

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In laboratory courses, standard procedure is to provide students with certain background information about an experiment before they actually perform it. This project aims to modify the pre-lab experience for students so that they can visually understand what is supposed to happen with the experiment. This will be done through the addition of performing simulations in COMSOL Multiphysics, which is a commercial finite-element software code. If students are required to do some computer simulation of parts of the experiment, it may help their understanding of the subject matter and aid them in gaining more knowledge from the laboratory experiment. The overall goals of the project are to: 1. Develop and test three different finite element models, detailed below, to help students better visualize the differential equations involved in the fluid flow experiment. a. Laminar flow in a straight pipe b. Laminar flow through a venturi and an orifice meter c. Laminar flow through a 90? elbow 2. Design short tutorials for new users of COMSOL to help them build the aforementioned finite element models. 3. Discuss areas of improvement in finite element models and provide recommendations. For laminar flow through a straight pipe, the theoretical and simulation values end up being equal to one another. The experimental values are slightly higher because of variations within the pipe as well as experimental error. For venturi and orifice meters, the different values match up well. For the venturi meter, the values are very close to each other. The simulation value for the venturi coefficient agrees with the accepted and the experimental values. For the orifice meter, however, the experimental and simulation values do not agree with the accepted value. The reason for this is that the accepted value for the orifice coefficient increases rapidly as Reynolds number decreases. The closest accepted value that was obtained was at a Reynolds number of over 4,000, and that value is 0.7. Thus, it is possible that there is a good correlation between the three values. For the 90? elbow, the Kf value from the experiment is certainly within the error range when compared to the simulation value, which approximates the theoretical value very well. Since it is not possible for the gages to measure very small differences between very large values, data was obtained only at a Reynolds number of around 2,000. For all three models, the COMSOL simulations approximate the physical situation well. For laminar flow in a straight pipe, COMSOL does very well, almost matching the theoretical and experimental results. For flow through venturi and orifice meters, COMSOL does well once again, giving good results for the venturi meter and results within the error range for the orifice meter. For flow through a through a 90? elbow, an experiment that had not been done before, the results turned out to be quite good, and it is possible that this experiment will be added to the lab in the future. Overall, simulation values for significant parameters fall within the error ranges for laboratory measurements. This means that students can use COMSOL before performing the experiment and get an idea for what the results are going to be like. Asking students to build and solve COMSOL simulations before performing experiments can help reinforce important concepts.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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