Supersonic Flow with suction phenomena on SimScale

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In today's tutorial, I would like to present the supersonic gas flow analysis with the suction phenomenon from the second inlet defined by pressure. For this type of analysis in SimScale we choose Compressible Flow Analysis which is used to model analyzes for gas velocities above 0.3 Mach Number.

Supersonic flow on SimScale

In the first step, we define the type of analysis (steady state) and the turbulence model (k-omega SST) (1). Then we define the type of gas that we will analyze in our geometry. Our choice is hydrogen as a compressible gas (perfect gas -2).

Settings for compressible flow on SimScale 

Then we define the boundary conditions. For Inlet 1, we define a speed of 390 m / s (343 m / s speed of sound limit) and a default temperature of 19 ° C.

Inlet 1 definition on SimScale

For Inlet 2, we define a pressure of 1 atm ABS so that the condition (more precisely, the flow direction from Inlet) depends on the conditions in the domain.

Inlet 2 definition on SimScale 

As an output from the model, we define a pressure outlet of 1 atm ABS. For compressible flows analyzes, pressure outlet is usually defined as the boundary condition of the model output to reduce the risk of generating computational errors related to residual equations.

Outlet definition on SimScale

We leave the Steady State analysis settings for the default conditions (number of steps - 1000, step size - 1). We only read the results for the final analysis iteration (1000 - Write Interval).

Steady State settings on SimScale 

As for the discretization, leave the Finess value at the default position (5). After generating the mesh, we get 423k finite elements and 150k nodes.

Generated mesh on SimScale 

After completing the calculations, we obtain the following velocity and temperature distributions on the model's cross-section (longitudinal cross-section).

Velocity distribution (magnitude) on cross-section of the model 

The figure below shows the volume distribution of gas velocity in the domain for a condition> 50 m / s. As we can see in the Inlet 2 zone, we have a fairly significant volume of gas with increased velocity, which proves the phenomenon of suction. This is mainly due to the very high gas flow (390 m / s) from Inlet 1, which creates a negative pressure which causes the above-described phenomenon.

Isosurface for velocity greater than 50 m/s 

As you can see, the very high gas pressures generated by the high velocities at inlet 1 increase the gas temperature (initial temperature in the domain and inlets 19.85 C).

Temperature distribution on cross-section 

One of my next suggestions for future SimScale software updates is adding the option to define the gas flow direction as Normal to Boundary. This is an option that is available in most CFD programs.

Proposition of additional option for defining BC's on SimScale 








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