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MID TERM REPORT

Submitted By:

Fouzia Begum (10-MS-PT-TF-05)

Kishwat Ijaz Malik (10-MS-FT-TF-04)

M. Ameer Ahsan (15-MS-FT-TSE-10)

UET Taxila

Submitted to:

Respected Sir Dr. Shehryar

Date of Submission:

6th April 2015

Project:

Characteristics of micronozzle gas flows

Project Supervisor: Dr. Shehryar

DEPARTMENT OF MECHANICAL ENIGINEERING

UNIVERSITY OF ENGINEERING & TECHNOLOGY TAXILA

April, 2015

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Table Of Content

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CHAPTER 1

Introduction to CFD and Literature Review:

Definition of CFD

Computational fluid dynamics is the branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems related to fluid flow. CFD simulations are run on high speed computers with excellent computational power to get better results.

CFD Simulation

Simulation is the reproduction of the operation of a real-world process or system over time. Validation of these simulations is done by experiments.

Background and History

The base of all the CFD problems is Navier-stokes equations which define any single phase fluid flow (gas or liquid but not both). The computer power available speed up development of three-dimensional methods. The first paper with three-dimensional model was published by John Hess and Smith of Douglas Aircraft in 1967. This method discretized the face of the geometry with panels, giving rise to this group of programs being called Panel Methods. Developers turned to Full Potential codes, as panel methods could not calculate the non-linear flow present at transonic speeds. The first description of a means of using the Full Potential equations was published by Earll Murman and Julian Cole of Boeing in 1970. The Navier–Stokes equations were the ultimate target of developers. Two-dimensional codes, such as NASA Ames' ARC2D code first emerged. A number of three-dimensional codes were developed (ARC3D, OVERFLOW, CFL3D are three successful NASA contributions), leading to numerous commercial packages.[1]

CFD Process

a) Geometry of problem is defined.b) Volume occupied by fluid cells is divided into discreet cells.c) Physical modeling is defined.d) Boundary conditions are defined.e) Analysis and visualization of resulting solution.

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CFD model of a convergent divergent nozzle problem

Importance of micro-nozzle in fluid flows

A nozzle is a basic device that offers thrust for the aerocraft system, and many small thrust nozzle systems have been used to maintain or adjust the orbit of space satellites.Since microsatellites appeared, they have needed a very fine control, which generally comes from small (mm) or micro (µm) nozzle systems. Therefore, the inner gas flows of micronozzles have become a focus, and it has been hoped that the understanding of the fluid characteristics could be helpful to the design of high performance. For the whole nozzle flows (in space), the gaseous fluids pass through all regimes, namely from continuum (chamber and convergent part of the Nozzle) to free molecular flow (far from the exit of the Nozzle), and it challenges the simulative capacity.[2]

History of convergent divergent nozzle

The converging-diverging nozzle is perhaps the most important piece of engineering hardware associated with propulsion and the high speed flow of gases. It was invented by a Swedish engineer Gustaf de Laval in 1888 and is thus often referred to as the 'de Laval' nozzle. This principle was first used in a rocket engine by Robert Goddard. Very nearly all modern rocket engines that employ hot gas combustion use de Laval nozzles.[3]

Literature on micro-nozzle

As for the experimental investigation, Rothe[4] used electron-beam techniques to measure the flow density and rotational temperature at some inner and outer points of the nozzle, and visualized the external flow structure. Boyd et al.[5,6] used coherent anti-Stokes Raman scattering techniqueto measure the velocity and translational temperature of the selected positions of the nozzle, and at the same time measured the thrust of the nozzle. In particular, they simulated the whole flow field, and the agreement proved that the DSMC could be applied to small nozzle flows. Then Broc et al.[7] gained the temperature and density of outer jet flows with laser-induced fluorescence technique, and Jamison et al.[8] measured the thrust with and without a divergent part versus Reynolds number. Because of the difficulty in the measurement of the micronozzle, now we can only get some data about its total performance. Bayt et al.[9] manufactured micronozzles with throat height of about 20−30 _m, and bytesting they pointed out that the viscous resistance affected flows mightily. Hao et al.[10] also manufactured micronozzles (throat height 20 µm), and determined the dependence of themass flux from the pressure difference (inlet’s pressure minus back pressure) by keeping pressure at the inlet and decreasing the environmental pressure (back pressure) that connected with the outlet of the nozzle.

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CHAPTER 2

Generation of mesh in Gambit

Introduction to Gambit

GAMBIT is a software package designed to help analysts and designers build and mesh models for computational fluid dynamics (CFD) and other scientific applications. GAMBIT receives user input by means of its graphical user interface (GUI). The GAMBIT GUI makes the basic steps of building, meshing, and assigning zone types to a model simple and intuitive, yet it is versatile enough to accommodate a wide range of modeling applications.

Generation of Nozzle mesh in Gambit

Step 1First of all set the appropriate coordinates upon which we have to build our nozzle.

Geometry Command Button ----> Vertex Command Button ---->Create Vertex Set the coordinates as:(0,0)(0,10)(95,0)(95,17)(-50,34)(-50,0)

Step 2In 2nd step we have to join our coordinate points to create the edges.

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Geometry Command Button ---->Edge command button ---->Create Edge By pressing shift button and clicking left by mouse on coordinate. It will appear red. Then click on second coordinate. Then click on apply command in the open window. Then an edge will appear. As shown in following figure,

By repeating the above procedure create all the faces, as shown in following,

Step 3

In this step we have to create all edges as one face, so computer can understand it that there is also something in this area except edges.

Geometry Command Button ---->Face command button ---->Form face By pressing shift button click left button of mouse on all edges to create the face. First edge will appear red. By clicking on all edges then click on apply command in the open window. Then all edges will appear as one face, as shown in following,

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Step 4In this step we have to divide all our edges in to number of nodes. One thing should be kept in mind that all the opposite faces must have equal number of nodes. Otherwise mesh will not be formed.

Mesh command button ---->Edge command button ---->Mesh Edges Then following window will appear

Change interval size to interval count and then click on the edge. And then give the appropriate number of nodes, after that click on apply. As shown in following,

Step 5In this step we have to mesh our face by doing the following steps,

Mesh command button ---->Face command button ---->Mesh face The following window will open

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By pressing shift button click left mouse button on one of the edge. Then all the edges will appear as red. The click on apply button. Mesh will be appear as follows,

Individual element should be approximately square for better calculations just like as follows,

And vertical lines should be parallel. Specially in throat section, as follows,

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Step 6In this step we have to examine our mesh. That it is following the criteria so that our solutions should be converged while doing calculations. For the examination of our mesh following are criteria’s,Criteria for mesh examination

a) Aspect ratio should be less than oneb) Worst element should not be in throat sectionc) Total elements should not exceed from 0.1million

For examination of mesh do the following steps in Gambit,

Click on Examine Mesh . Following window will open,

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For examination, check Range in Display Type. Check as 2D Element. And in Quality Type check as Aspect Ratio. As seen from the figure total elements are 64000. And Aspect Ratio is 3.

Examination of Worst Element

As seen from the figure the worst element is on left wall. So it is acceptable that worst element is not in throat section.

Step 7In this step we have to apply the necessary boundary condition on our particular problem. As in our case,Left Wall is pressure inletRight Wall is pressure outlet.Upper two walls are chosen as Wall.

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Lower wall is chose as symmetric wall.For Boundary Conditions do the following in Gambit,

Zones Command Button ---->Specify Boundary Type Command ---->then following window will open.

First of all click on edge and then check the type from above command and then click on apply button. After applying boundary conditions this window will open as,

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Step 8In this we will export our file as mesh file to solve the problem in Fluent.Go to File Menu Bar---->Export---->mesh. A window will open, click on accept. Our mesh file will be saved in our directory.

After this our work in Gambit will be finished. Whenever we have to work on Gambit, we have to follow the above 8 steps for generation of our mesh.

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CHAPTER 3Simulation in Fluent

Introduction to Fluent

ANSYS fluent is engineering simulation software. By using this software one can solve the problem in a virtual environment. By using fluent we can do the followingFlow problems in 2D and 3D

Compressible & Incompressible Steady state and time dependent Variety of material properties Complex physics & chemistry Inviscid, viscous, and turbulence models Complex geometries & meshes Multiple and non-inertial reference frames Quantitative analysis & visualization

Following are the steps by which we can run our simulation in fluent for our nozzle problem.

Step 1First of all open your mesh file in fluent.Go to File Menu Bar---->Read---->Mesh.This will open your mesh file in fluent. As Shown in following,

Step 2In this step we have to choose what is our problem nature and type.In our particular problem,Type = Pressure BasedProblem Nature = Steady2D Space = PlannerAs shown in following,

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Step 3In this step we have to choose our model. Basically it is our mathematical model which will be solved from one node to another node.As shown in following,

Step 4In this step we have to choose our material as solid/fluid.In our particular case fluid is entered as air and solid is as aluminum. Because our wall of nozzle are solids and we have choose them as aluminum.Following figure shows in fluent,

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Step 5In this step we have to apply our boundary conditions and their values.In our particular case,Pressure inlet = 101325 PaPressure Outlet= 65000 PaDo it in fluent by clicking on boundary conditions and then select particular boundary condition and then click on create/edit. A window will open as shown in following,

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Similarly do it for outlet boundary condition.

Step 6In this step we have to choose our solution method, as shown in following,

Step 7In this step we have run our calculation.Number of iterations = 1000And then click on run calculation. Fluent will calculate all the results until our solution converges. If our solution will not converge then fluent will show a message that solutions are going to diverge at particular node then we have to check our meshing criteria and again follow the above steps.Following window is to run the calculations,

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CHAPTER 4Results and Validation

Article ResultsWe have to validate results of the article which has been assigned to us in class. Following are the author’s generated results which we have to validate through ANSYS Fluent.

Description of Author’s Results

H3 is the height of nozzle at outlet. Back pressure is applied at outlet. Knudsen number (Kn2) is at throat section and Knudsen number (Kn3) is at nozzle outlet. λ is the mean free path of the gas molecules. Re2 is the Reynolds number at throat section. Re3 is the Reynolds number at nozzle outlet.

Formulas for the Calculations

Kn= λH

ℜ=UHρμ

= mμ

λ= 165 √ kT

2 πmμP

Fluent Results

References

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1. M. Raciti Castelli, P. Cioppa and E. Benini,”Numerical simulation of the flow field around the 30 degree flat plate” World Academy of Science, Engineering and Technology 63 2012.

2. Xie, Chong. "Characteristics of micronozzle gas flows." Physics of Fluids (1994-present) 19.3 (2007): 037102.

3. http://cfdblogvienna.blogspot.com/p/computational-fluid-dynamics-advanced-a.html 4. Rothe, Dietmar E. "Electron-beam studies of viscous flow in supersonic nozzles." AIAA Journal

9.5 (1971): 804-811.5. Boyd, Iain D., et al. "Experimental and numerical investigations of low-density nozzle and plume

flows of nitrogen." AIAA journal 30.10 (1992): 2453-2461.6. Boyd, Iain D., Douglas B. VanGilder, and Edward J. Beiting. "Computational and experimental

investigations of rarefied flows in small nozzles." AIAA journal 34.11 (1996): 2320-2326.7. Broc, Alain, et al. "Experimental and numerical investigation of an O $ _ {2} $/NO supersonic

free jet expansion." Journal of Fluid Mechanics 500 (2004): 211-237.8. Jamison, A. D., and A. D. Ketsdever. "Low Reynolds number performance of an underexpanded

orifice and a Delaval nozzle." Rarefied Gas Dynamics 23rd, edited by AD Ketsdever and EP Muntz (AIP, New York, 2003) (2003).

9. Bayt, Robert L. Analysis, fabrication and testing of a MEMS-based micropropulsion system. Aerospace Computational Design Laboratory, Dept. of Aeronautics & Astronautics, Massachusetts Institute of Technology, 1999.

10. Hao, Peng-Fei, et al. "Size effect on gas flow in micro nozzles." Journal of Micromechanics and Microengineering 15.11 (2005): 2069.