Computational Fluid Dynamics Lab (PFC–IV) AY 2022-23
Lab No. : 6
Name of the Lab: External flow
Name of Student: Shubham Vijay Jadhav Roll No. 222
Section/ Batch: C4 Date of Submission: 24/3/24
1. Introduction:
The flow around a circular cylinder is a simple flow and has been studied for long time.
However, it is often by gaining a deeper understanding of simple phenomena that we learn
useful lessons for wider contexts. This project shows some of the results of numerical
simulations that modelled laminar flow around a circular cylinder. An understanding of this
flow can yield insights into the flow fields surrounding airplanes, submarines, buildings
1. Aim:
Simulate the flow over the cylinder and explain the phenomenon of Karman
vortex street: Von Karman effect — vortex shedding
• Simulate the flow with steady and unsteady case and calculate the Strouhal
Number.
• Calculate the coefficient of drag and lift over a cylinder by setting the Reynolds
number to 10,100,1000,10000 & 100000 (run with steady solver)
• Discuss the efffects of Reynolds number on the coefficient of drag (results
should be validated with any standard literature and error should be within 5%)
• Plot the coefficient of drag and lift.
• Plot to show vortex shedding behind the cylinder.
2. Objectives:
To Study and understand the Karman vortex street phenomenon.
• To create a 2D geometry of given dimensions and Generate fine enough mesh
and inflation layers around the cylinder wall.
• Simulate, 1) At Re = 100, simulate the flow with steady and transient method
and calculate the Strouhal number. 2)For the given Reynolds number values
calculate the coefficient of drag and coefficient of lift over a cylinder.
• Discuss the effects of reynolds number on coefficient of drag.
• Plot the graphs of coefficient of drag and coefficient of lift.
• Plot to show vortex shedding behind the cylinder.
• Write down the detailed report of the project
3. Methodology:
1. Geometry Preparation:
- Create or import the geometry of your external flow domain into ANSYS Fluent.
Ensure cleanliness and proper definition. Simplify geometry if needed.
2. Mesh Generation:
- Generate a suitable mesh for your geometry. Choose structured or unstructured mesh
types based on complexity. Pay attention to boundary layer resolution.
3. Boundary Conditions and Model Selection:
- Define boundary conditions for inlet, outlet, walls, etc. Specify fluid properties.
Choose turbulence models and other relevant models (e.g., heat transfer) based on flow
characteristics.
4. Solver Setup:
- Configure solver settings, including convergence criteria, solution methods, and
initialization options. Start with a coarse mesh and refine gradually.
5. Solution Initialization and Convergence:
- Initialize the flow field based on defined boundary conditions and initial conditions.
Ensure stability of the solution. Run the simulation, monitor convergence, and adjust
settings or mesh refinement as needed.
6. Post-Processing, Validation, and Reporting:
- Analyze results using ANSYS Fluent's post-processing tools. Visualize flow patterns,
pressure distributions, etc. Validate results against experimental data or analytical
solutions. Document methodology, assumptions, and results for reporting.
Following these steps will help you effectively simulate external flows using ANSYS
Fluent, providing valuable insights into fluid behavior around external objects or
geometries.
4. Geometry: Provide images detailing the steps involved in creating the geometry.
5. Meshing: Present images illustrating the meshing process including methods, sizing,
inflation, etc.
6. Governing Equations:
• Continuity Equation: Also known as the conservation of mass equation, it
states that the rate of change of mass within a control volume is equal to the net
rate of mass flow into or out of the control volume.
• Momentum Equations: These equations describe the conservation of
momentum in the fluid flow.
• Energy Equation: This equation describes the conservation of energy in the
fluid flow and includes terms for convection, diffusion, and energy generation.
• These equations form the basis for solving fluid flow problems in CFD.
Depending on the specific problem and assumptions made (e.g., steady-state vs.
transient, compressible vs. incompressible), additional equations or
simplifications may be applied. Overall, solving these governing equations
numerically allows engineers and scientists to simulate and analyze complex
fluid flow phenomena in various applications.
7. Solution Technique/Set-up: -
8. Result and Discussion:
Result: External Flow Simulation in ANSYS Fluent
ANSYS Fluent enables precise modeling and analysis of external flow phenomena.
From geometry preparation to post-processing, its tools facilitate accurate simulation
and insightful analysis, empowering engineers to optimize designs and understand fluid
behavior efficiently.
9. Conclusion:
In conclusion, simulating external flow using ANSYS Fluent offers engineers and researchers a
powerful toolset for understanding fluid behavior around objects or bodies immersed in a fluid
medium. By leveraging ANSYS Fluent's comprehensive capabilities in geometry preparation,
mesh generation, solver setup, and post-processing, users can conduct accurate and insightful
analyses of external flow phenomena.
The ability to define boundary conditions, select appropriate turbulence models, and validate
simulation results against experimental data enhances the reliability and confidence in the
obtained insights. ANSYS Fluent facilitates the optimization of designs, the identification of
performance enhancements, and the resolution of engineering challenges related to external
flow scenarios.
Overall, ANSYS Fluent serves as an indispensable asset in the field of computational fluid
dynamics, empowering users to make informed decisions, improve designs, and advance
understanding in the realm of external flow dynamics.
