Week 2 - Flow over a Cylinder.

Flow over a Cylinder

To simulate the flow over a cylinder and explain the phenomenon of Karman vortex street, we will perform the following tasks:

PART-I: Flow Simulation and Strouhal Number Calculation

• Set up a flow simulation of the flow over a cylinder using a computational fluid dynamics (CFD) software, such as ANSYS Fluent.
• Perform simulations for both steady and unsteady cases.
• Set the Reynolds number (Re) to 100 by varying the velocity of the flow while keeping the dimensions of the cylinder constant.
• Define the geometry of the cylinder and specify the boundary conditions (inlet velocity, outlet pressure, etc.).
• Choose a suitable turbulence model, such as the k-epsilon or k-omega model, for the simulation.
• Run the simulations and monitor the solution residuals to ensure convergence.
• To determine if the flow has converged, examine the convergence plots of the solution residuals. Look for a steady and consistent behaviour, where the residuals reach a sufficiently low and constant level.
• Calculate the Strouhal number (St) using the formula: St = f * D / U, where f is the vortex shedding frequency, D is the diameter of the cylinder, and U is the freestream velocity.
• Compare the Strouhal number obtained from the steady and unsteady simulations to observe the phenomenon of Karman vortex street.

PART-II: Coefficient of Drag and Lift Calculation

• Set up a flow simulation using the steady solver in ANSYS Fluent.
• Vary the Reynolds number (Re) by adjusting the flow velocity, while keeping the cylinder dimensions constant.
• Define the geometry, boundary conditions, and other simulation settings.
• Choose a suitable turbulence model for the simulation, such as the k-epsilon or k-omega model.
• Run the simulations and monitor the solution residuals to ensure convergence.
• To determine if the flow has converged, examine the convergence plots of the solution residuals. Look for a steady and consistent behaviour, where the residuals reach a sufficiently low and constant level.
• Calculate the coefficient of drag (CD) and coefficient of lift (CL) for each Reynolds number using the formulas provided by ANSYS Fluent.

Compare the calculated coefficients of drag for each Reynolds number and analyse the effect of Reynolds number on the drag coefficient.

Validate the results by comparing them with standard literature, ensuring that the error is within 5%. Use reference papers or fluid mechanics textbooks to verify the obtained results.