Space Shuttle Document

8/10/2019 Space Shuttle Document

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an "stablished industrial design tool, helping to reduce design time scales and

improve processes throughout the engineering world.

1.2.2 Governing Equations

Conservation of mass

/ate of increase of mass in fluid element equals the net rate of mass flow into

the element.

Conservation of momentum

2omentum is conserved in x , y , direction 3 from the %ewton4s second

law( F5ma) the momentum equations in all three direction is derived as,

Conserved in 6 direction



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1.2.3 Advantages of Cfd

Relatively o! Cost

o 9sing physical experiments and tests essential engineering data for

design can be expensive.

o CF simulations are relatively inexpensive, and costs are li$ely to

decrease as computers become more powerful.

"peed

o CF simulations can be executed in a short period of time.

o :uic$ turnaround means engineering data can be introduced early in

the design process.

A#ility to "imulate Real Conditions

o 2any flow and heat transfer processes cannot be (easily) tested, e.g.

hypersonic flow.

o CF provides the ability to theoretically simulate any physical

condition.

A#ility to simulate ideal conditions


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o CF allows great control over the physical process, and provides the

ability to isolate specific phenomena for study.

o "xample; a heat transfer process can be idealied with adiabatic,

constant heat flux, or constant temperature boundaries.

Compre$ensive Information

o "xperiments only permit data to be extracted at limited number

locations eat transfer for electronics pac$aging applications.

1.3 Cfd %et$odology

1.3.1 Initial &esign


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1.3.2 C'& modeling

-he first tas$ to accomplish in a numerical flow simulation is to extract the fluid

domain or the region where the fluid flow is occurring. 9sing the Cfd tools the

geometrical components which are all not needed for the simulation is removed

thus only the fluid domain is prepared for the next process.

1.3.3 %es$ Generation

?ne of the most cumbersome and time consuming part of the CF is the mesh

generation. 1lthough for very simple flows, mesh generation is easy, < t

becomes very complex when the problem has many cavities and passages, 2esh

generation is basically the discretiation of the computational domain. -he mesh

in finite difference methods consists of a set of points, which are called nodes.

-he finite volume methods consider points that form a set of volumes which are

called cells. -he finite element methods used sub&volumes called elements

which have nodes where the variables are defined. =alues of the dependent

variables, such as velocity, pressure, temperature, etc. are described for each

element.

=arious forms of elements can be used. >owever, the most common type in

CF programs is a hexahedron with eight nodes, one at each corner, and this is

$nown as a bric$ element or volume. For two&dimensional applications the

equivalent element is a four&node quadrilateral. #ome finite volume programs

have now been released which have the ability to use tetrahedral in three

dimensions or triangles in two dimensions. 2ost finite element CF codes will

allow these elements to use together with a small range of other element types.

1.3.( "urface %es$ing

-his pac$age provides a function template to compute a triangular mesh

approximating a surface. -he meshing algorithm requires to $now the surface to


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be meshed only through an oracle able to tell whether a given segment, line or

ray intersects the surface or not and to compute an intersection point if any. -his

feature ma$es the pac$age generic enough to be applied in a wide variety of

situations. For instance, it can be used to mesh implicit surfaces described as the

ero level set of some function.


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1.3.) *olumetric %es$es

=olumetric meshesare a polygonal representation of the interior volume of an

obBect. 9nli$e polygon meshes, which represent only the surface as polygons,

volumetric meshes also discretie the interior structure of the obBect.

?ne application of volumetric meshes is in finite element analysis, which may

use regular or irregular volumetric meshes to compute internal stresses and

forces in an obBect throughout the entire volume of the obBect.


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.3.+ %es$ ,uality Criteria

Cell ,uality

o "quiangle s$ew

o "quivolume s$ew

o 1spect ratio

"-e!

#$ewness is defined as the difference between the shape of a cell and the shape

of an equilateral cell of equivalent volume. >ighly s$ewed cells can decrease

accuracy and destabilie the solution. For example, optimal quadrilateral

meshes will have vertex angles close to * degrees, while triangular meshes

should preferably have angles of close to E* degrees and have all angles less

than * degrees. 1 general rule is that the maximum s$ewness for a

triangulartetrahedral mesh in most flows should be $ept below *., with an

average value that is significantly lower. 1 maximum value above *. may

lead to convergence difficulties and may require changing the solver controls.

Equiangle s-e!


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5 largest angle in the face or cell

5 smallest angle in the face or cell

5 angle for an equiangular face or cell (e.g., E* for a triangle and * for a

square)

Equivolume s-e!


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o -hese integral equations are converted to a system of algebraic equations

by generating a set of approximations for the terms in the integral

equations.

o -he algebraic equations are solved iteratively. 1n iterative approach is

required because of the non&linear nature of the equations, and as the

solution approaches the exact solution, it is said to converge. For each

iteration an error, or residual, is reported as a measure of the overall

conservation of the flow properties.

o >ow close the final solution is to the exact solution depends on a number

of factors, including the sie and shape of the control volumes and the

sie of the final residuals. Complex physical processes, such as

combustion and turbulence, are often modeled using empirical

relationships. -he approximations inherent in these models also

contribute to differences between the CF solution and the real flow.

o -he solution process requires no user interaction and is, therefore, usually

carried out as a batch process. -he solver produces a results file which is

then passed to the post&processor.

1.(.3 /ost /rocessing

-he post&processor is the component used to analye, visualie and present the

results interactively. !ost&processing includes anything from obtaining point

values to complex animated sequences.

"xamples of some important features of post&processors are;

o =isualiation of the geometry and control volumes

o =ector plots showing the direction and magnitude of the flow

o =isualiation of the variation of scalar variables (variables which have

only magnitude, not direction, such as temperature, pressure and

speed) through the domain

o :uantitative numerical calculations

o 1nimation


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o Charts showing graphical plots of variables

o >ardcopy and online output.

1.(.( "oft!are tools used

o Cad modeling tool0 #olid wor$s I*'I

o /reprocessing tool0 1%#1, 1%#7#&- G/


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o "xample; Flow in a duct with sudden expansion.


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Hhen the flow is symmetrical about some plane there is no flow through the

boundary and the derivatives of the variables normal to the boundary are ero.

Cyclic or /eriodic 4oundaries

-hese boundaries come in pairs and are used to specify the flow has the same

values of the variables at equivalent position and both of the boundaries.

/ressure 4oundary Conditions

-he ability to specify a pressure condition at one or more boundaries of a

computational region is an important and useful computational tool. !ressureboundaries represent such things as confined reservoirs of fluid, ambient

laboratory conditions and applied pressures arising from mechanical devices.

Generally, pressure condition cannot be used at boundary where velocities are

also specified, because velocities are influenced by pressure gradients. -he only

exception is when pressures are necessary to specify the fluid properties. ".g.,

density crossing a boundary conditions, referred to as static or stagnation

pressure conditions.


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unsteady (turbulent) motions affecting the flow that cannot be resolved directlyK

they must therefore be modeled.


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o #patial resolution requirement is no longer governed by the

Oolmogorovs micro&scaleP He can tac$le high /eynolds numbers and

determine the resolution based on required engineering accuracy

cad model

'.base model

height50. m

width5 m

length5 m


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space shuttle capsule

space shuttle capsule with wind tunnel

pre&processing

'.base model

wind tunnel construction

front5 QJ

bac$5 J

side5IJ

where,

J5 height of capsule


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surface mesh count5EE'*I

s$ewness5*.E

volume mesh count5IQ0I cells

s$ewness5*.Q

'8E C6&II6"

"olver "ettings

a#le ).1 "olver "ettings

!rocessing #erial

#olver coupled, !ressure @ased


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imension 0

/ro#lem "etupa#le ).2 /ro#lem "etup

2aterials

-ype !roperties 9nit

Fluid 1ir

ensity&'.II

Cp &'**E.Q0

$&*.*IQI

=iscosity&

'.e

&

Og20

Og $

H2$

Og2s

#olid titanium

ensity&I'

Cp&'

$&I*I.Q

Og20

Og $

H2$

-urbulence 2odelling #pallart&allamars

"nergy "quation ?n

Cell 8one Condition Fluid&1ir

4oundary Conditions

a#le ).3 4oundary Conditions

Fluid Flow -hermal


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"quation

solved

FlowConservation of mass

Conservation of momentum

"nergy Conservation of energy

-urbulence -urbulence modelling& spallart

allmaras

"oft!are 8sed

a#le ).) "oft!are 8sed

!re&!rocessing1nsa

omain "xtractionGeometry Cleanup

#urface 2eshing

#urface 2esh

Cleanup

1nsys&-grid =olume 2eshing

#olver

1nsys&Fluent

Fluid Flow 1nd

-hermal@ehaviour

!ost&!rocessing 1nsys&Fluent "nd results


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post &processing

'.base model for 2a5I

contours of static pressure around the capsule along the surface


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contours of static temperature around the capsule along the surface

contours of density around the capsule along the surface


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contours of velocity magnitude around the capsule along the surface

conclusion.

-hus, the space re &entry shuttle capsule is analysed for the mach

number(2a5I). -hus, the post&processing results of the flow field

around the capsule when capsule attains 2a5I is predicted. when

flow is above 2a5*.0, the flow nature changes to compressible flow,

so, the fluid experiences pressure change around the capsule results in

shoc$ waves and also due to compressibility , the fluid density

changes. ue to high pressure and viscous force, it experiences the

high temperature distribution to the fluid and also to the capsule, due

to tangential shear forces of fluid .

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