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Who Wants to Be a CFD Expert?. In the ME 566 course title, CFD for Engineering Design , what does the acronym CFD stand for? Car Free Day Cash Flow Diagram Computational Fluid Dynamics Lifelines Phone a Friend Ask the Audience. ME 566 Project. Mixing in a Model Combustor

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Who Wants to Be a CFD Expert?

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Who Wants to Be a CFD Expert?

  • In the ME 566 course title, CFD for Engineering Design, what does the acronym CFD stand for?

    • Car Free Day

    • Cash Flow Diagram

    • Computational Fluid Dynamics

  • Lifelines

    • Phone a Friend

    • Ask the Audience


ME 566 Project

  • Mixing in a Model Combustor

    • You are to determine the effect that the angle of the side inlets has on mixing in the combustor.

T.-M. Liou and Y.-Y. Wu,

Experimental Thermal and Fluid Science 1992, 5:401-409.


  • Tasks

    • You can choose a single angle of 5, 10, 15, or 20 away from the perpendicular side inlets.

    • 3 cases to study

+

1

2



3


  • Physical dimensions of the combustor

    • The length unit is in mm

15

120

15

15

Y

Y

30

1.58

X

Z

2000


  • Experimental setup

    • Hydrocarbon gas mixture is supplied through the axial inlet

    • Air is supplied through the two side inlets

    • The combustor bulk mean velocity is 23.9 m/s

    • The combustor Reynolds number is 4.56104

Air

Gas mixture

Air


  • Comments

    • The experimental results can be used as a guideline.

    • To augment the experimental findings on mixing, you can set the temperatures of the side inlet and axial jets to different values and use temperature as a passive fluid marker (i.e. solve the thermal energy equation with no buoyancy force).

Tside

Assume adiabatic at walls

CFX-Pre:

- Buoyancy Option:Non Buoyant

- Heat Transfer Option: Thermal Energy

Taxial


Project Report

  • You report should include

    • a comment on the validity of the CFD simulation for the perpendicular angle based on comparison to experimental data

    • a clear statement of your findings on the effect of the side inlet angle on mixing within the combustor

    • a clear presentation of the computational model’s geometry, boundary conditions and properties. Wherever possible, quantify the influence that the two most significant model parameters have on your solution


  • You report should include

    • a description of the basis of your geometry and mesh designs

    • a comment of the applicability of the k model for this flow

    • a statement on the degree of convergence obtained by the solver

15

120

15

15

Y

Y

30

1.58

X

Z

2000


Y* = 2

L

Y* = 1

Y* = 0

X* = 0

Frequently Asked Questions (FAQs)

  • How to create a side inlet with an angle :

    • Draw a line with dimension L (where L = 15 mm)

    • Draw a line with dimension L/cos (where = 5 ~ 20)

    • Join two lines together (Constraints  Coincident)

    • Specify the angle  between two lines (Dimensions  Angle)

4

L/cos

2

L

3

1


  • What fluid properties should be used for hydrocarbon gas mixture?

    • You can assume the gas mixture has the same properties as air

  • What entrance velocity should be used?

    • One way to find out entrance velocity is to read U/Uref and V/Uref from Tables 1A and 1B, where Uref = 23.9 m/s

  • What turbulence intensity and length scale values should be used?

    • One way to find out turbulence intensity is to read u’/Uref and v’/Uref from Tables 1A and 1B

    • For length scale, select the turbulence option: Intensity and Auto Compute Length


  • Inlet velocity and turbulence intensity for the side inlet can be found from Table 1A at Y* =  2

  • For example, at Y* = 2:

    • V/Uref = 8.26E-1 at X* = 0.25

    • v’/Uref = 1.03E-2 at X* = 0.25

    • (V/Uref)avg = 8.27E-1

    • (v’/Uref)avg = 1.09E-2

X* = 0

X* = 0.5

Y* = 2

Y* = 1

Y*

Y* = 0

X*


  • How to define velocity at the inlet with side angle?

    • Mass and Momentum Option  Cart. Vel. Components u = -Vsin (m/s), v = -Vcos (m/s), w = 0 (m/s)

V

V

Vcos

Vsin


Questions?


Order of Accuracy

  • A certain discretisation scheme is used to estimate the temperature in a rectangular fin. The computations are done with a uniform mesh having a spacing of x. Table 1 shows the variation of the predicted heat flux at the base of the fin, , with the mesh spacing.

  • Q1: Estimate the order of accuracy of the numerical method. The exact heat flux is 214.3 [watts].

  • Q2: The order appears to decrease for the finer meshes. What numerical errors are affecting the solutions obtained with fine meshes?

Table 1


  • : error, a: constant, x: mesh spacing, n: order of accuracy

  • The order of accuracy is first order


Who Wants to Be a CFD Expert?

  • The order of accuracy appears to decrease for the finer meshes. What numerical errors are affecting the solutions obtained with fine meshes?

    • Discretisation error

    • Round-off error

    • Truncation error

  • Lifelines

    • Phone a Friend

    • Ask the Audience


Numerical Errors (Sec. 10.2)

  • Round-off error

    • Round-off errors are the result of the computational representation of real numbers by means of a finite number of significant digits, which is termed the machine accuracy.

  • Discretisation error / Truncation error

    • The discretisation error is associated with the neglected contributions due to the truncation of high-order terms.

Taylor series expansion


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