FORCED CONVECTION SIMULATION FOR HT2 EXPERIMENT

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FORCED CONVECTION SIMULATION FOR HT2 EXPERIMENT

• MAE 427
• Mechanical Aerospace Engineering
• Cornell University

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Experiment vs. Modeling

• Modeling Well use FlowLab software
• FlowLab uses the computational modeling approach
  to obtain an approximate solution to the
  governing equations. Referred to as Computational
  Fluid Dynamics (CFD).
• Will use nominal data in simulation. You need to
  redo with your data.

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Strategy of CFD

• Eg. Continuous Domain p p(x), 0ltxlt1
  Discrete Domain pi p(xi), i1,2,,N
• Truncation error introduced. Can be reduced by
  refining the grid.
• Grid refinement study required to assess the
  level of truncation error.

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Geometry Step

• Assume flow is axisymmetric. Hence, domain is
  rectangular.
• Rotate the rectangle 360o about the axis to get
  the full pipe geometry

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Geometry Step

• Length of pipe included in the simulation From A
  to D
• Tip To restore original views, use the following
  buttons at the bottom right of the GUI

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Physics Step

• Incompressible ideal gas Neglect variations in
  absolute pressure in ideal gas law
• Properties use average values over temperature
  range
• Reynolds no. 100,000 Turbulent flow regime

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Physics Step Turbulence

• Cannot resolve rapid fluctuations in turbulent
  flow
• We solve only for averaged quantities
• Need to augment governing equations with
  turbulence model equations (additional
  approximation!).

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Physics Step Turbulence

• Will use k-e turbulence model.
• Workhorse in engineering calculations (but has
  problems).
• k turbulent kinetic energy Measure of the
  kinetic energy of velocity fluctuations u, v
  and w.
• e turbulent dissipationMeasure of the
  dissipation of k into internal energy.
• See lab manual for more details.

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Physics Step

• Operating condition
• Gauge pressure Absolute pressure Reference
  pressure
• Inlet boundary condition (BC)
• Assume velocity is constant across cross-section.
• Use guess values of k and e. Well specify low
  turbulence levels.
• Axis BC FlowLab imposes symmetry conditions.

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Physics Step

• Outlet BC
• Outlet pressure needs to be specified. Use
  measured gauge pressure at D.
• Outlet velocity and temperature come out of the
  simulation.
• Wall BC
• FlowLab imposes no-slip condition for velocity.
• We specify the measured (constant) heat flux in
  the heated section.
• Well assume wall is smooth ((wall thickness
  0).
• Well neglect heat conduction within pipe wall
  (wall thickness 0).

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Solve Step

• Since governing equations are nonlinear,
  iterations are required to solve the equations.

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Post-Processing Step

• Temperature contours Is the flow well-mixed at
  the end of the adiabatic mixing section?

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Post-Processing Step

• Velocity vectors in the first section showing
  flow development.

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Reports Step

• Pressure variation along pipe axis. Yellow
  symbols represent experimental values.
• Can export these values in Excel format.

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Reports Step

• Temperature variation along pipe axis. Yellow
  symbols represent experimental values.

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Reports Step

• Wall temperature variation. Shows thermal
  entrance length effects.

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Reports Step

• Nusselt number distribution.
• Can average values in the heated section to
  compare with experiment.
• Dont use friction factor values from FlowLab.

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Reports Step

• Axial velocity profiles at various locations.
• Plot shows flow is nearly fully developed as it
  enters the heated section.
• Shows flow is accelerated in the heated section.

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Reports Step

• Temperature profiles at various locations.
• Plot shows temperature is nearly uniform at the
  outlet (end of the mixing section).