This model examines both scenarios.Īn outlet pressure of 16.05 psi is applied for the weak shock and 14.10 psi for the strong shock. The wave either causes the flow to separate (a “strong” shock) or stay together (a “weak” shock). Once the flow is supersonic, a shock wave brings it back to subsonic speeds. The model geometry of the Sajben diffuser. As the flow moves through the diffuser, it accelerates to sonic conditions in the throat and supersonic conditions in the diverging part (where the geometry starts to expand). Note that this diffuser is transonic with a turbulent flow that starts out as subsonic. In the model, fluid (i.e., air) travels through a convergent-divergent diffuser. Sajben and his team in their benchmark experiments and simulations. The diffuser in this example uses the geometry from M. Modeling a Transonic Diffuser with the CFD Module To take these factors into account and design optimized transonic diffusers, engineers can use the COMSOL Multiphysics® software and add-on CFD Module, as discussed in this benchmark example. Image in public domain, via Wikimedia Commons.Īn optimized diffuser makes for a better supersonic aircraft engine, but designing this component can be a challenge, as it involves unsteady fluctuations, high speeds, shock waves, and flow separation. Ramjets can be found in various supersonic aircraft, such as the SR-71 Blackbird featured above.

By increasing the pressure, the diffuser also helps enhance the performance of the combustor, which in turn makes the aircraft more fuel efficient.

The diffuser slows down the airflow in the engine to subsonic speeds so that it doesn’t extinguish the burner and also helps minimize flow losses. For instance, ramjets (also called “flying stovepipes”) are a type of air-breathing jet engine that use diffusers as inlets. These abilities are useful for various applications, including helping HVAC systems evenly distribute air, reducing pressure losses in supersonic ejectors, minimizing turbulence in centrifugal pumps, and reducing drag in race cars.ĭiffusers are important components in supersonic aircraft propulsion systems. Slowing Supersonic Speeds with Transonic Diffusers As this benchmark model illustrates, these complex phenomena can be accurately analyzed using the COMSOL® software. To design transonic diffusers for supersonic applications, engineers must account for factors like high-speed turbulent flow and shock waves. For example, diffusers are often used in supersonic aircraft like ramjets to slow down fluid flow and increase static pressure. From home HVAC systems to spacecraft ejectors, diffusers find use in all kinds of applications.

Comsol multiphysics tutorial fluid flow