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Transonic Flow in a Sajben Diffuser

Application ID: 10407

In this model the high speed turbulent gas flow in a converging and diverging nozzle is modeled using the High Mach Number Flow interface. The diffuser is transonic in the sense that the flow at the inlet is subsonic, but due to the contraction and the low outlet pressure, the flow accelerates and becomes sonic (Ma = 1) in the throat of the nozzle.

After a short region of supersonic flow, a normal shock wave brings the flow back to subsonic flow. This setup has been studied in a number of experiments and numerical simulations by M. Sajben and co-workers, in an effort to study unsteady fluctuations in supersonic inlets with applications in supersonic aircraft propulsion systems. The geometry and setup is often referred to as a Sajben diffuser and constitutes a common test case for the simulation of high Mach number internal flows.

In this model the time averaged transonic flow through a Sajben diffuser is solved for using two different exit pressures. The flow in the diffuser is fully turbulent with a inlet Reynolds number of 7x105 based on the inlet fluid properties and the channel height. The model uses the Spalart-Allmaras turbulence model to compute the turbulent viscosity.

This model is included as an example in the following products:

CFD Module

The combination of COMSOL® products required to model your application depends on several factors and may include boundary conditions, material properties, physics interfaces, and part libraries. Particular functionality may be common to several products. To determine the right combination of products for your modeling needs, review the Specification Chart and make use of a free evaluation license. The COMSOL Sales and Support teams are available for answering any questions you may have regarding this.