Week 4 - CHT Analysis on Exhaust port

Aim:

To simulate an internal flow of the exhaust port and study for the Conjugate heat transfer in the simulation.

Objectives:

1. Give a brief description of why and where a CHT analysis is used.
2. Maintain the y+ value according to the turbulence model and justify the results.
3. Calculate the wall/surface heat transfer coefficient on the internal solid surface & show the velocity & temperature contours in appropriate areas.
4. How would you verify if the HTC predictions from the simulations are right? On what factors does the accuracy of the prediction depend on?

CHT (Conjugate heat transfer):

Conjugate heat transfer corresponds with the combination of heat transfer in solids and heat transfer in fluids. In solids, conduction often dominates whereas in fluids, convection usually dominates. Conjugate heat transfer is observed in many situations.Conduction is observed within same kind of molecules (within a solid), convection occurs between different kind of molecules where bulk motion is involved (between solid and fluid).

The Conjugate Heat Transfer (CHT) analysis type allows for the simulation of heat transfer between solid and fluid domains by exchanging thermal energy at the interfaces between them.

Conjugate Heat Transfer. In solids, conduction often dominates whereas in fluids, convection usually dominates. Conjugate heat transfer is observed in many situations. For example, heat sinks are optimized to combine heat transfer by conduction in the heat sink with the convection in the surrounding fluid.

Challenge approach:

In this challenge we have to follow five major steps Geometry, meshing, set-up, solution and result. then we have to solve two case simulation in exhaust port. using ANSYS Fluent solver to create the geometry and perform unstructured tetra CFD mesh with boundary definitions. velocity of 5 m/s and k-omega SST model. Below I mentioned the two cases of element size.

Case Baseline element size (mm) Inflation layer element size (mm)

Case 1 150 150

Case 2 50 20

Procedure to simulate the conjugate heat transfer analysis on exhaust port:

• First we need to import geometry to the geometry space claim window, Then extract fluid volume, After give the share topology, the finished model is attached below.
• Next open mesh window then generate mesh by giving some mesh length, Then create inflation layer but before that keeping in mind of what turbulent model we using, We calculate the first inflation layer thickness Then that criterion we give to the inflation layers this meshed model and quality criterion.
• After mesh close mesh window open setup window, There we enable the energy equation, selecting the sst omega viscous model, Select the material for fluid and for solid, Under the cell zone condition for inside exhaust port volume select the fluid material and for the exhaust shell select solid material
• Then give the boundary condition, intialize the problem and from report under definition option take out the surface heat transfer coefficient graph sheet then run the simulation for the iteration where it will converge.
• After the calculation we taking out the contour graph for velocity by creating the plane, and taking out the pressure, Temperature contour plot as well.
• In the report option under using surface integral option we taking out the result of heat transfer coefficient at the inflation and also taking out the results of (maximum/ minimum) velocity, temperature, pressure, at entire as well at the outlet position.
• So similarly to take out the wall surface heat transfer coefficient contour graph at the post process we export the solution data by clicking the file and select the export and click solution data option and save it in fluent file by giving file type as CDAT file, Then open post process window click on the file select load file import the data from file file where it saved So by this we read the result this result is attached.
• So by this we run the simulation for two case study case1 having the mesh length of 150mm, case2 having the mesh length of 50mm.

Step 1: Geometry

Volume exract image:

Share topology image:

Step 2: Meshing

• clicking on the GENERATE MESH it will create a mesh automatically. We should create a INFLATION layers for the fluid volume outer surface with 0.5 mm as first layer thickness with 6 layers and 1.2 as growth factor.
• Since we already used share topology option, the mesh will look good. For case 1, and then go to GENERATE MESH and input size as 150 mm for inflation layer and the base mesh size will be 150 mm. For case 2, and then go to MESH > INSERT > SIZING and input size as 50 mm for inflation layer and the base mesh size shall be 20 mm.
• We should give name for the geometry Inlet, Outlet, Convection Wall and inflation layer. the fluid volume outer surface and name it as inflation layer. Once we completed the meshing process after that we have to move next set-up process.

CASE 1 MESH IMAGE:

CASE 2 MESH IMAGE:

3) Problem Setup :

• To set up our problem we open Fluent and setup inital conditions , boundary conditions material etc.,
• We first start with checking the mesh quality using perform mesh check under domain.If no error is seen in console window then we can proceed further.
• Then we move to setting up physics where we select the solver ,viscous model ,initial and boundary conditions etc.,
• We use a steady state pressure based solver to solve our model.

Physics :

General :

Solver type : pressure based

time : steady state

velocity formulation : absolute

models :

viscous model : k-omega SST

Material : Fluid : Air

Solid : aluminum

Zones :

Cell zone : In cell zones you will see fluid volume,it is of type fluid with material air and solid volume it is of type solid with material aluminum.

Boundary conditions :We will basically give our boundary conditions here such as inlet velocity and outlet conditions.

we can give,

Inlet :

velocity : 5 m/sec

temperature : 700K

Outlet :

pressure outlet : gauge pressure = 0 pa

Outer wall convection :

type : wall

Theremal conditions => convection : Heat transfer coefficient = 20 W/m^2 K

• Now if you check other BC they are just wall boundaries we are not changing anything we are going to ignore them.
• Now we are almost ready to run the simulation ,but as the solution is being solved we want to moniter different flow quantities while the solution is being generated ,we create contour for this.But before that we have to initialize the domain.We use the Hybrid initialization , this provides a very good initial condition.
• Now we want to see the temperature contour.
• For contour -> go to solutions tab -> graphics -> contour -> in contour of : select temperature under that select static temperature -> select the outer walls and press save /display.
• then we can do calculation for 150 iteration.

Result:

CASE 1 RESIDUAL PLOT

CASE 2 RESIDUAL PLOT

CASE 1 HTC PLOT

CASE 2 HTC PLOT

CASE 1 Temperature contour

CASE 2 temperature contour

CASE 1 velocity contour

CASE 2 velocity contour

CASE 1 surface heat transfer contour

CASE 2 surface heat transfer contour

CASE 1 velocity stramline contour

CASE 2 velocity stramline contour

CASE 1 velocity volume rendering contour

CASE 2 velocity volume rendering contour

CASE 1 surface heat transfer coefficient contour

CASE 2 surface heat transfer coefficient contour

Case 1 Case 2

Baseline mesh 150 50

Inflation layer mesh 150 20

No. of elements 242050 309852

Surface heat transfer coefficient 21.25 21.34

Conclusion:

• Hence by above procedure the simulation run successfully.