cascadexpert help

7/28/2019 Cascadexpert Help

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CASCADExpert

Table of Contents

Chapter 1. Introduction .................................................................................... 2Chapter 2. Installing CASCADExpert ................................................................... 2

System requirements ....................................................................................... 2Installing from the CD [verify] ........................................................................... 2Uninstalling CFA ............................................................................................... 2

Chapter 3. Getting started ................................................................................ 3Creating a new project ..................................................................................... 3The geometry .................................................................................................. 3The inflow angle .............................................................................................. 4The results ...................................................................................................... 5

Chapter 4. Generating or loading a geometry ...................................................... 6Generating a geometry ..................................................................................... 6Loading an existing geometry ............................................................................ 7Viewing geometry elements .............................................................................. 9Chapter 5. Computing ...................................................................................... 9Changing the inflow angle ................................................................................. 9Convergence analysis ......................................................................................10

Chapter 6. Analyzing the results .......................................................................10Data displayed on screen .................................................................................10Analyzing streamlines ......................................................................................11Pressure coefficient .........................................................................................12Average velocity components ...........................................................................14Velocity colour map .........................................................................................14Pressure colour map ........................................................................................14Streamline velocity .........................................................................................14

Chapter 7.

Customizing the display settings .......................................................14

Toolbar ..........................................................................................................14Status bar ......................................................................................................15Zoom ............................................................................................................15

Chapter 8. Resources ......................................................................................15Chapter 9. Feedback .......................................................................................15


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Chapter 1. Introduction

CASCADExpert is an interactive software for cascade hydrodynamics. This version issolving the incompressible, inviscid irrotational flow for a given cascade geometry. A

carefully selected pre- and post-processing procedures are selected, in order to provideboth flexibility in describing the problem and efficient quantitative and qualitative flowanalysis.

CASCADExpert uses a finite element solver for the streamfunction boundary valueproblem, with robust and efficient implementation of periodic conditions as well as ofKutta-Joukovski condition. Thanks to the FEM formulation, the numerical differentiationof the solution is completely avoided in the processing step. Accurate velocity

computation in the post-processing step is achived using the Superconvergent PatchRecovery method. The system of equation is solved using a Bi-Conjugate GradientMethod, which provides the required robustness and accuracy with minimum computing

time.

CASCADExpert has been used and tested for more than three years in both researchand education activities. It provides an user-friendly environment for both design and

analysis problems, and it is an excellent tool for teaching cascade hydrodynamics topics.

CASCADExpert is an evolving software. The present platform is currently expanded tosolve viscous problems using a robust fully-coupled viscous-inviscid algorithm, as well asto include energetic and cavitational optimization strategies. For Q3D turbomachinerycomputations, a variable thickness streamsurface is being implemented.

Chapter 2. InstallingCASCADExpert

System requirements

Software requirements

CFArequires one of the following operating systems to be installed:

Windows 2000 Professional orWindows XP orWindows Server 2003

Hardware requirements

PC with a 400 MHz or faster processorMinimum 256 MB RAM, recommended 512 MB RAM

HDD space: 10 MB for the application, up to 15 MB for data

CD-ROM or DVD driveSuper VGA (800x600) or higher resolution monitor recommendedKeyboard and Microsoft Mouse, or compatible pointing device

Installing from the CD [verify]

Insert the CASCADExpert CD into your CD-ROM drive.The CD should autoplay.If it does not autoplay, navigate to the drive representing your CD unit (forexample E:). Double-click E:\setup.exe and then follow the instructions onthe screen.

Uninstalling CFA

You can uninstall the application by navigating to the Add/RemovePrograms utility: Click on Start, Settings, Control Panel, Add/Remove


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Programs. Select Change/Remove for the CFA application and then followthe instructions on the screen

Chapter 3. Getting started

After you have installed the application you are ready to start using it. When the

application starts, you will have a new project already set up. If you want to start over,you can create a new project at any time.

Next steps:

Creating a new projectThe geometryThe inflow angleThe results

Creating a new project

To create a new project, on the main menu, select File, New.

You will see a window similar to the one below.

Next steps:

The geometryThe inflow angleThe results

The geometry

Once the new project has been created you need to specify the cascade geometry.that defines the problem. From the main menu, select Geometry, Generate....


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A wizard will show up (as seen above on the right) letting you choose the method fordefining the hydrofoil shape. The first choice is to pick-up a NACA foil. You will be

successively asked for the NACA foil name, number of points used for discretizing thehydrofoil (200 is a reasonable choice), stagger angle and spacing. With these dataCASCADExpert generates the computational domain and its mesh. For example,

In the lower right corner fo your window you will find information on mesh size (number

of nodes, number of elements). The number of nodes +1 is the size of the linear systemof equations to be solved. The additional equation comes from the Kutta-Jukowskicondition that sets the circulation.

For more informationFor more information, please readChapter 4, Generating or loading a geometry

Next steps:

The inflow angle

The results

The inflow angle

The only flow parameter for this problem setup in the inflow angle. From Compute

Input Flow Angle you will get and dialog box for providing the inflow angle value. Oncethe value is validated, CASCADExpert builds the linear system of equations and solves for

the nodal values of the streamfunction, as well as for the flow deflection angle.


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For more information

For more information, please readChapter 5, ComputingNext step:

The results

The results

After the system of equations is solved, the main numerical results are displayed in the

left side of your window (see below). For example, you get the outflow angle (the mainparameter that quantifies the flow deflection), as well as the circulation around thehydrofoil and the corresponding axial and tangential force coefficients.

Besides these global quantitative parameters, one can examine the qualitative aspect ofthe streamlines (above right), in order to see the location of the leading edge stagnationand the degree the flow is distorted. The number of streamlines is always odd since atleast the stagnation streamline and the streamlines defining the periodic strip aredisplayed. Moreover, as seen in theAnalyze panel, several other flow quantities can beexamined. Among them, the most important one is the pressure coefficient distribution

on the hydrofoil.


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The pressure coefficient definition can be chosen with respect to various referencevelocity/pressure values (inlet, outlet, etc.) and the values are displayed in a plottingwindow, where numerical values are also available for quantitative assessment. Ifnecessary, experimental data can be added on the plot in order to assess the accuracyand the validity of the inviscid flow model.

Chapter 4. Generating or loading a geometry

Generating a geometry

A key step in designing the hydrofoil shape is the ability of generating a large variety of

suitable streamlined body shapes. CASCADEexpert provides several robust and efficient

procedures to construct the hydrofoil with the precision specified by the used (number ofpoints on the hydrofoil surface).One possibility is to use analytically defined hydrofoils, like the well-known NACA family.The Hydrofoil Shape Wizardwill guide you through the four steps of specifying thegeometry and the mesh refinement, as shown below. Clicking the Finish button in thelast panel completes the geometry and mesh generation.


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The Hydrofoil Shape Wizardwill once again guide you through the geometry generationprocess, as shown above. Once UIUC Data Base is selected, a file panel becomes

available to choose one foil file. After loading, the wizard displays the airfoil name andthe number of points available in the file. At this point the user must choose among fourreconstruction methods. The first one is None, meaning that exactly the points from thefile will be used for domain generation and mesh refinement. The next two are spline

interpolations. The spline for sharp trailing edge allows different tangent slopes at thetrailing edge from suction and pressure sides, respectively. The round trailing edgeoption uses a periodic spline in order to represent foils like the one below.

This low pressure gas turbine blade is provided as an example in the last wizard option.

Another format available for point coordinate file is the one compatible with TECPLOTdata file, which can be easily understood by saving a hydrofoil from FileSaveFoilmenuand examining the ASCII file structure.


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Viewing geometry elements

After going through the geometry generation procedure, the user can examine thehydrofoil shape (to make sure the input is correct and accurate), as well as the

computational domain shape and the unstructured triangulation.

Chapter 5. Computing

In order to compute the flow, the user must specify the inlet flow angle. TheCASCADExpert convention is that the flow angle is measured with respect to the cascade

front line. The actual computation does not require any input from the user.

Changing the inflow angle

For the same cascade geometry, one can analyze the flow field for several values of the

inflow angle, without reconstructing the hydrofoil and the computational domain. Bysimply going to ComputeInput Flow Angle, the dialog box below will allow the

introduction of a new value.


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Convergence analysis

In various stages of the CASCADExpert development, having a control of the iterativesolution procedure convergence is quite useful. This is how we have determined that theBi-Conjugate Gradient Method is the best suited approach for our problem. Theconvergence behaviour can be visualized from ComputeDisplay Convergence, which willproduce a plot like this one:

Chapter 6. Analyzing the results

Data displayed on screen

Once a problem is solved, the upper-left side panel shows the main data concerning theproblem definition and global results.


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Analyzing streamlines

Up to 19 streamlines can be displayed for a periodic strip. Note that in comparison with

the computational domain, the streamline picture was reconstructed in order to show anintuitive picture of the flow field. From AnalyzeStreamlines the user is prompted to the

dialog box where the number of streamlines must be specified.


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The stagnation streamline is normal to the solid surface at the stagnation point, asproved theoretically for the irrotational flow (for example the picture below)

Pressure coefficient

The pressure coefficient is the dimensionless representation of the pressure distributionon the hydrofoil. Several pressure distribution definitions are available, in order to

accommodate the user needs. The last one allows for an arbitrary pressure coefficient


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distribution consistent with the Bernoulli theorem either in absolute or relative flow.

The plotting window will show both thep

c versus the dimensionless chordline abscissa

distribution, as well as the numerical values for a quantitative evaluation.

By clicking the right mouse button on the plotting window, the user can set the plot

appearance according to the options below.


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Average velocity components

This feature is aimed at providing a robust and accurate procedure for velocitycomponents averaging in the front-line direction. The corresponding Q2D cascade modelprovides the cascade loading as well as the blade blockage coefficient for later use in a

Q3D turbomachinery analysis/design procedure.This feature will be available in the next release.

Velocity colour map

Velocity components and velocity magnitude can be examined qualitatively using a colormap. This feature proved very useful for educational purposes, as it clearly shows theregions with strong flow acceleration or deceleration.This feature will be available in the next release.

Pressure colour map

Pressure in the computational domain can be examined qualitatively using a color map.

This feature proved very useful for educational purposes, as it clearly shows the regionswith minimum pressure values, where cavitation can occur.This feature will be available in the next release.

Streamline velocity

Chapter 7. Customizing the display settings

Below are a few features that can help you optimize your experience with the CFAproduct:

Toolbar

Select or deselect this option if you want the toolbar to be seen or not. This is howthe toolbar looks:

Options on the toolbars are:

create new project

save the project data

print

show the foil


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show the domain

show the mesh

show residual information

show streamlines

show the pressure coefficient distribution

display the qualitative representation of the velocity

display the quantitative representation of the velocity

show contextual help

show the help index

Status bar

The status bar displays contextual information. For example, after generating ageometry, the status bar will display the number of nodes and the number ofelements for the mesh.

Zoom

Zoom in our out into the graphical display on the main screen.

Chapter 8. ResourcesFor additional resources on this subject please read the following articles (available for

public download):www.vitalsoft.ro/cfa/exampledoc.pdf

Chapter 9. Feedback

Please send your feedback about the product at:[email protected]

Regarding scientific issues, please send your comments to:Romeo [email protected]
http://www.vitalsoft.ro/cfa/exampledoc.pdfhttp://www.vitalsoft.ro/cfa/exampledoc.pdfmailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.vitalsoft.ro/cfa/exampledoc.pdf

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