## Terminal Velocity, Drag Coefficients, and FIFA World Cup™ Predictions

##### Ed Fontes June 1, 2018

Every four years, people interested in association football/soccer (a few billion people) talk about the FIFA World Cup™. We at COMSOL are no exception. During coffee breaks and lunches, we are discussing the different teams, players, preparations, and the tiny details that might impact the teams. The ball is an important protagonist of the games. The subject of the ball combines our passion for soccer and physics into one discussion!

### Modeling Free Surfaces in COMSOL Multiphysics® with Moving Mesh

##### Ed Fontes May 31, 2018

In a previous blog post, we discussed using field-based methods (level set and phase field) for modeling free surfaces. Another option, moving mesh, can handle free liquid surfaces that do not undergo topology changes. In this blog post, we will demonstrate how to use the moving mesh method for modeling free surfaces and compare the results with field-based methods.

### Analyzing Multiphase Flow in an Airlift Loop Reactor Benchmark Model

##### Thomas Forrister May 23, 2018

Multiphase flow involves the simultaneous flow of fluids of different phases, such as gases and liquid, or solid particles suspended in a fluid. As such, modeling multiphase flow can require multiple approaches. One approach is to use a bubbly flow model to analyze the effects of bubble-induced turbulence. Here, we discuss a benchmark model of liquid and gas flow in a water-filled airlift loop reactor and validate the simulation results with experiments.

### Two Methods for Modeling Free Surfaces in COMSOL Multiphysics®

##### Ed Fontes May 15, 2018

There are four methods for modeling free liquid surfaces in the COMSOL Multiphysics® software: level set, phase field, moving mesh, and stationary free surface. In the first part of this blog series, we discuss the level set and phase field methods, which are field-based methods that describe almost any type of free liquid surface. In part two, we will compare the results from this post with those obtained using the Moving Mesh interface for solving free surface problems.

### How to Solve a Classic CFD Benchmark: The Lid-Driven Cavity Problem

##### Angela Straccia May 8, 2018

The lid-driven cavity is a popular problem within the field of computational fluid dynamics (CFD) for validating computational methods. While the boundary conditions are relatively simple, the flow features created are quite interesting and complex. Here, we demonstrate how to define this benchmark problem in the COMSOL Multiphysics® software. We also showcase techniques like mapped meshing and nonlinearity ramping, which can be applied to a wide variety of CFD models.

### Modeling Fluid-Structure Interaction in a Heart Valve

##### Caty Fairclough April 25, 2018

The average human heart beats around 100,000 times in a single day. With each beat, the four valves within the heart open and close, transporting blood unidirectionally through its chambers. By simulating heart valves, medical researchers can study their behavior to address various cardiac health issues. As an example, a team from Veryst Engineering modeled a heart valve opening and closing with the COMSOL Multiphysics® software.

### Analyzing Wastewater Contaminant Removal in a Secondary Clarifier

##### Thomas Forrister April 24, 2018

Wastewater often contains organic and inorganic materials, which can be nonbiodegradable and even toxic. To reuse wastewater, these contaminants are removed via physical, chemical, and biological processes. Clarifiers treat wastewater by separating the particles via sedimentation, but their performance is affected by factors such as settling, turbulence, the ratio of the particles’ outer surfaces to mass, sudden direction changes in the flow, and the velocity profile. To design clarifiers for effective wastewater treatment, engineers can turn to fluid flow simulation.

### Analyzing a Supersonic Ejector with CFD Simulation

##### Caty Fairclough April 16, 2018

Ejectors have many applications, such as removing debris in outer space and providing refrigeration at your local supermarket. To improve ejectors for these and other uses, engineers aim to find optimal designs and operating conditions as well as accurately describe the flow within these devices. Simulation can help achieve these goals.

### Using the Algebraic Multigrid (AMG) Method for Large CFD Simulations

##### Ed Fontes March 26, 2018

The algebraic multigrid (AMG) solver provides robust solutions for large CFD simulations. Available as of version 5.3a of the COMSOL Multiphysics® software, the AMG method only requires one mesh, in contrast to the geometric multigrid (GMG) solver, which requires at least one extra coarser mesh. This eliminates the hassle associated with creating coarse meshes for complex geometries with small details that are difficult to mesh unless a fine mesh is used.

### Using the Inflow Boundary Condition in Nonisothermal Flow Simulations

##### Nicolas Huc March 15, 2018

Nonisothermal flow combines CFD and heat transfer analysis. In cases where the temperature of the fluid at an inlet is a known quantity, a Temperature boundary condition can be used. However, there are some important situations where this is not the case, and an Inflow boundary condition can improve the model accuracy and reduce the computational cost of the simulation. Here, we review how this more sophisticated thermal boundary condition can be set at a flow inlet.

### Comparing Static and Dynamic Wall Heat Exchangers with Simulation

##### Bridget Paulus February 27, 2018

Due to their small size and efficiency, compact heat exchangers are used in many application areas, including HVAC, nuclear power, and electronics. To help increase heat transfer rates and reduce pressure drops in these devices, a large number of studies have been performed, exploring concepts such as incorporating a deforming wall into the design. Using the COMSOL Multiphysics® software, you can evaluate a dynamic wall heat exchanger design.