Fluid mechanics lab report example

Few notes about the lab report

Introduction Computational Fluid Dynamics could be a term used to describe any method of modelling flow fields using computing techniques. We will only be looking at one of the methods available to us in this course: the finite volume method. Using a single volume gave a single change in the bulk properties of the fluid at the inlet and outlet of the control volume in the presence of some known boundary conditions. CFD uses a similar approach, breaking the flow field into many volumes, which allows us to resolve the flow field in more detail. Between the inlet and outlet boundaries of neighbouring volumes the boundary conditions are shared. The problem, of course is that we do not know the internal boundary conditions, so even for the simplest flow field the computation must make an initial guess of these boundary conditions, and then iterate towards a solution where equations of continuity, momentum, and depending on what is required energy are satisfied for each of the sub- control volumes. The CFD process is summarised in figure 1. Your objective is simply to write a report by following the CFD process below. In particular, in writing your report follow the process shown in figure 1 and explain all 5 parts (physics, grid etc.) for your case. After explaining the CFD process, your focus will be on analysing and validating your CFD results using the experimental data ( see below, part 5: Analyse ). So, use your lab experiment data in part 5 for validations (this is a good place to include all your lab experimental data!).

Figure 1 CFD process

Procedure

1- In introduction explain a little bit your case for example for the case of flow in pipes and Moody diagram or for the case of flow over an aerofoil explain what NACA0020 means.

2- You can use all the CFD lecture notes which are available in ELP (formulas, figures etc., simply copy if you would like) when you are writing your report. Similar graphs for both CFD simulations are also available in the lecture notes.

3- In particular you can explain the type of model you use ( e.g. model 1: AFD, model 2: EFD and model 3:CFD) and follow the CFD process used to explain flow over a cylinder ( see CFD lecture notes and also figure 1 below)

4- The key parameter you need to compare with experimental data for the aerofoil lab experiment is the Cp, and for the compressible lab experiment is the head (pressure) loss.

5- You need to compare only one case for each experiment: -For the Lab1: the pipe with 34mm Diameter

- For the aerofoil: the case with 10 degrees angle of attack

6- I have provided the mesh for both cases above in CFD parts of leaning materials in ELP. Copy the files in your directory.

Simply open ANSYS workbench 18. Drag the Fluid flow ( CFX) into work bench.

Then right click on the mesh, and import the mesh.

Remember to change the extension to .msh in order to see the mesh file and import it. *

*Note: Please ask those who have attended the IT sessions if you were absent or if you are not sure how to do this.

Click in Setup: Use an appropriate boundary condition:

See above how to insert boundary conditions ( right click on default)

For both simulations: For inlet you can use velocity inlet, estimate it form your experiment. For out let you use ‘outlet’ and set relative pressure as zero For solid walls ( e.g. aerofoil body and pipe’s wall) use no-slip wall For aerofoil simulations: For the aerofoil simulation use symmetric boundaries for all other planes around the aerofoil, these are called far field boundary.

Here also you can change few parameters for example, you can increase the number of iterations and reduce the target residual in ‘ solver control’ to obtain results that are more accurate. In Solution: Press Run to solve it in this section.

You need to include a graph of convergence in your report, see below.

In results you can extract all the contours and data, results, …

Obviously, you are not expected to do everything form scratch. If you are interested, you can use ANSYS tutorial to learn more. For example you may carry out tutorials for geometry creation in Design Modeler, mesh generation in ANSYS Meshing, and the solution of the of the flow field in CFX, they are all available online. This module was not devoted to CFD but the fact that you are getting familiar with CFD in an early stage is great! The key point you need to consider in your report is to compare your experiment with the CFD and discuss the validation process and the source of errors and uncertainty for CFD and EFD.