1、Fluid #2: Velocity analysis of fluid flow in a channel USING FLOTRANIntroduction: In this example you will model fluid flow in a channelPhysical Problem: Compute and plot the velocity distribution within the elbow. Assume that the flow is uniform at both the inlet and the outlet sections and that th
2、e elbow has uniform depth.Problem Description:The channel has dimensions as shown in the figure The flow velocity as the inlet is 10 cm/s Use the continuity equation to compute the flow velocity at exit Objective: To plot the velocity profile in the channel To plot the velocity profile across the el
3、bow You are required to hand in print outs for the above Figure: IMPORTANT: Convert all dimensions and forces into SI unitsSTARTING ANSYS Click on ANSYS 6.1 in the programs menu. Select Interactive. The following menu comes up. Enter the working directory. All your files will be stored in this direc
4、tory. Also under Use Default Memory Model make sure the values 64 for Total Workspace, and 32 for Database are entered. To change these values unclick Use Default Memory Model MODELING THE STRUCTUREGo to the ANSYS Utility Menu (the top bar) Click WorkplaneWP Settings The following window comes up: o
5、 Check the Cartesian and Grid Only buttonso Enter the values shown in the figure above Go to the ANSYS Main Menu (on the left hand side of the screen) and clickPreprocessorModelingCreateKeypointsOn Working PlaneCreate keypoints corresponding to the vertices in the figure. The keypoints look like bel
6、ow.Now create lines joining these key points. ModelingCreateLinesLinesStraight line The model looks like the one below. Now create fillets between lines L4-L5 and L1-L2.Click ModelingCreateLinesLine Fillet. A pop-up window will now appear. Select lines 4 and 5. Click OK. The following window will ap
7、pear: This window assigns the fillet radius. Set this value to 0.1 m. Repeat this process of filleting for Lines 1 and 2. The model should look like this now: Now make an area enclosed by these lines. ModelingCreateAreasArbitraryBy Lines Select all the lines and click OK. The model looks like the fo
8、llowing The modeling of the problem is done. ELEMENT PROPERTIESSELECTING ELEMENT TYPE: Click PreprocessorElement TypeAdd/Edit/Delete. In the Element Types window that opens click on Add. The following window opens. Type 1 in the Element type reference number. Click on Flotran CFD and select 2D Flotr
9、an 141. Click OK. Close the Element types window. So now we have selected Element type 1 to be solved using Flotran, the computational fluid dynamics portion of ANSYS. This finishes the selection of element type.DEFINE THE FLUID PROPERTIES: Go to PreprocessorFlotran Set UpFluid Properties. On the bo
10、x, shown below, set the first two input fields as Air-SI, and then click on OK. Another box will appear. Accept the default values by clicking OK. Now were ready to define the Material PropertiesMATERIAL PROPERTIESWe will model the fluid flow problem as a thermal conduction problem. The flow corresp
11、onds to heat flux, pressure corresponds to temperature difference and permeability corresponds to conductance. Go to the ANSYS Main Menu Click PreprocessorMaterial PropsMaterial Models. The following window will appear As displayed, choose CFDDensity. The following window appears. Fill in 1.23 to se
12、t the density of Air. Click OK. Now choose CFDViscosity. The following window appears: Now the Material 1 has the properties defined in the above table so the Material Models window may be closed. MESHING: DIVIDING THE CHANNEL INTO ELEMENTS:Go to PreprocessorMeshingSize CntrlsManualSizeLinesAll Line
13、s. In the window that comes up type 0.01 in the field for Element edge length. Now Click OK. Now go to PreprocessorMeshingMeshAreasFree. Click the area and the OK. The mesh will look like the following. BOUNDARY CONDITIONS AND CONSTRAINTSGo to PreprocessorLoadsDefine LoadsApplyFluid CFDVelocityOn li
14、nes. Pick the left edge of the outer block and Click OK. The following window comes up. Enter 0.1 in the VX value field and click OK. The 0.1 corresponds to the velocity of 0.1 meter per second of air flowing from the left side. Repeat the above and set the Velocity to ZERO for the air along all of
15、the edges of the pipe. (VX=VY=0 for all sides) Once they have been applied, the pipe will look like this: Go to Main MenuPreprocessorLoadsDefine LoadsApplyFluid CFDPressure DOFOn Lines. Pick the outlet line. (The horizontal line at the top of the area) Click OK. Enter 0 for the Pressure value. Now t
16、he Modeling of the problem is done.SOLUTION Go to ANSYS Main MenuSolutionFlotran Set UpExecution Ctrl. The following window appears. Change the first input field value to 300, as shown. No other changes are needed. Click OK. Go to SolutionRun FLOTRAN. Wait for ANSYS to solve the problem. Click on OK
17、 and close the Information window. POST-PROCESSINGPlotting the velocity distribution Go to General PostprocRead ResultsLast Set. Then go to General PostprocPlot ResultsContour PlotNodal Solution. The following window appears: Select DOF Solution and Velocity VSUM and Click OK. This is what the solut
18、ion should look like: Next, go to Main MenuGeneral PostprocPlot ResultsVector PlotPredefined. The following window will appear: Select OK to accept the defaults. This will display the vector plot to compare to the solution of the same tutorial solved using the Heat Flux analogy. Note: This analysis
19、is FAR more precise as shown by the following solution: Go to Main MenuGeneral PostprocPath OperationsDefine PathBy Nodes Pick points at the ends of the elbow as shown. We will graph the velocity distribution along the line joining these two points. The following window comes up. Enter the values as shown. Now go to Main MenuGeneral PostprocPath OperationsMap onto Path. The following window comes up. Now go to Main MenuGeneral PostprocPath OperationsPlot Path ItemsOn Graph. The following window comes up. Select VELOCITY and click OK. The graph will look as follows:
