Steady State Simulation of Flow in a throttle body

Steady State Simulation of Flow in a throttle body

A steady state simulation generally means that with time there are no changes in the flow once it has fully developed.

In a steady state simulation the throttle inside the plane must be assumed to be stationary and water flowing over its boundaries.

The geometry of an elbow pipe with throttle valve is shown below.

Effect of gravity has been neglected for simplication, air flows through the horizontal bend and then the flow gets disturbed due to the presence of throttle valve just before the turn.

Base Grid is taken as 0.002 m in all the three directions.

Because the values of different parameters change the most when flowing over the throttle boundaries, so refining of the mesh here is necessary for precision computation results.

To do so fixed embedding has been done around the boundary of the throttle, a scale of 3 has been taken, which basically means that our mesh gets refined 3 times, and 2 embedded layers are taken for further refining.

Mesh around the throttle is shown below.

Boundary Conditions

In total four boundaries have been initialised.

• Inlet -  Boundary type is INFLOW, a total pressure of 1.5e5 Pas has been given and     with a temperature of 300k
• Outlet -Boundary type is OUTFLOW, static pressure of 1e5 Pas has been given, this pressure difference of 0.5e5 Pas will cause the flow of Air to take place.
• Wall - The wall is the covering surface of the geometry, the boundary condition assigned is Wall type, with no slip condition enabled.
• Throttle - Throttle valve is also set as Wall. 

General Properties

Pressure based steady state solver was chosen since it is a steady state solver. Effect of gravity has been neglected and nothing else has been changed from default.

Simulation Parameters

• Run Parameters
  • Simulation Mode - Full Hydrodynamic.
  • Gas Flow solver -  Compressible
• Simulation Time parameters
  • Total Number of cycles to run - 10000.
  • Time Step Selection -  Variable Time step Algorthim.
  • Inital Time Step - 1e-09
  • Minimun Time Step - 1e-09
  • Maximum Step - 1
  • Maximum Convection CFL limit - 1.
  • Maximum Diffusion CFL limit - 2.
  • Maximum Mach CFL limit - 1.
  • Rest every thing hasn\'t been chnaged from default.
• Turbulence Model taken is RNG k-ε.

Running the Simulation.

The biggest issue with the cfd simulation is that the time needs to be sufficiently small th capture the flow accurately but at the same time it needs to be big to reduce the computational time.

However, in this simulation we\'ve asssumed the time selection method to be variable based on the CFL numbers limits.

Results

The computational time was around 60 mins using a laptop with 4 cores and running the simulation in parallel on two processors. As Expected.

(a) Flow velocity becomes zero at the walls of the throttle.

(b) Solution converges after around 7000 cycles.

Velocity Profile is shown below.

Flow has fully developed and the solution has converged perfectly.

The regions where the velocity becomes small due to the presence of Throttle valve is shown below.(blue regions)

Plots showing the Convergence of different parameters with respect to the number of cycles is shown below.

• Mass Flow at inlet v/s Number of cycles.

• Mass Flow at outlet v/s Number of cycles.

• Average Velocity at Inlet v/s Number of cycles.

• Average Velocity at Oultet v/s Number of Cycles.