# Converging-diverging nozzle

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 July 13, 2018, 12:55 Converging-diverging nozzle #1 New Member   Join Date: Jul 2018 Posts: 6 Rep Power: 2 So I'm new to Fluent and I'm trying to do a simulation of a Converging-diverging nozzle. For starts, I'm considering inviscid flow. I'm supposed to obtain a supersonic flow downstream the throat followed by a normal shock. However, I can't seem to achive these two phenomena. I think I'm messing something up setting the BC. Here's what's given: * Mach number inlet: Ma= 0.239543 * Stactic pressure inlet: p_s_inlet=1 bar=10^5 Pa * Stactic pressure outlet: p_s_exit =0.83049*p_s_inlet * Total temperature inlet: 300 K I calculated the total inlet pressure using the Mach number and pressure relation. Set the Operating Pressure to 0, so I can work with absolute pressures. Here's what my inlet and outlet BC look like: Pressure Inlet: https://imgur.com/a/KzFpodi Pressure Outlet: https://imgur.com/a/F9JPnLE I'm working with air as an ideal gas. I set the inlet BC to Pressure Inlet because of compressibility. So, any ideas why I can't get to the results I need? Do you guys see anything wrong with the BC? I fully appreciate and look forward to your replies. Thanks in advance. Note: if imgur hosting is not appropriate I can change it. Sorry for anything. UPDATE: here are the contours of Mach numbers for the simulation with the BC above. It's converged in 2015 iterations. https://imgur.com/a/6kQxMOf

 July 13, 2018, 19:12 #2 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 3,188 Rep Power: 39 Is the throat area small enough to choke the flow?

 July 14, 2018, 06:08 #3 Senior Member   Behrooz Jamshidi Join Date: Apr 2013 Posts: 107 Rep Power: 7 This is not a CFD problem. First of all your flow needs to be choked. Choked flow is independent of geometry. For air as working fluid, your discharge pressure must be less than 0.53*Pinlet. While you set discharge pressure as 0.83* Pinlet, it is obvious that you can not get choked flow and subsequently shock. Leonardo.flores likes this.