CFD Simulation B Y : E V A N N E Y 1 2 / 1 6 / 1 4 Converging - PowerPoint PPT Presentation

Converging Diverging Nozzle CFD Simulation B Y : E V A N N E Y 1 2 / 1 6 / 1 4

Converging Diverging Nozzle - Background Hour glass shaped nozzle HIGH  Fully subsonic isentropic flow  Velocity increases in converging section and decreases Inlet of decreasing cross sectional area   in diverging section Outlet of increasing cross sectional area Flow becomes choked (Mach 1 at throat)   Upper limit of back pressure range for shocks  Used to accelerate pressurized fluid to  Converging section becomes time independent Outlet (Back) Pressure  supersonic speeds Normal shock wave is formed near throat  Instantaneous property changes across shock  Useful in many turbine and jet engine  Pressure increase  applications. Temperature increases  Velocity decreases  Shock wave location moves towards outlet  Shock is just at outlet. More complex shock  patterns begin to occur Flow pressure at exit is less than ambient pressure –  Overexpanded nozzle Fully supersonic isentropic flow (design  condition) Lower limit of back pressure for shocks in  overexpanded flow Back pressure low enough that it equals the nozzle exit  pressure Shocks disappear  𝒆𝑩 𝑩 = 𝒆𝑾 𝑾 (𝑵 𝟑 − 𝟐) LOW Reference 1

Project Aims This project aims to This project aims to 1) 2) examine inviscid and examine viscous real flow in a 3D boundary layer supersonic converging separation with shock diverging nozzle and waves in an over the development of expanded supersonic normal shocks in the nozzle. nozzle.

Geometry and Mesh Geometry  Best mesh:  The nozzle profile will aligned Profile:   with that tested by Craig Edge sizing with number of  Hunter, NASA (profile depicted divisions per section below) Bias towards wall  Sweep:  Throat area At =4.317 in^2  Swept through the width with  Expansion ratio Ae/At = 1.797  bias towards edges Width 3.99in Mirrored over symmetry plane  

ANSYS Fluent Setup INVISCID MODEL TURBULENT MODEL Solver Settings:  Solver Settings:  Steady solver  Steady solver  Density based (as the flow is compressible)  Density based (as the flow is compressible)  Inviscid model  K-Epsilon/K-Omega  2 nd order upwind 2 nd order upwind/1 st order upwind   Boundary conditions:  Boundary conditions:  Pressure inlet at inlet  Pressure inlet at inlet  Pressure outlet at outlet  Pressure outlet at outlet  No slip wall on sides and top plane  No slip wall on sides and top plane  Symmetry on bottom plane of model  Symmetry on bottom plane of model  Material Properties:  Material Properties:  Working fluid was standard air  Working fluid was standard air  Air as ideal gas model  Air as real gas (Soave Redlich Kwong)  NPR = inlet total pressure / outlet pressure

Inviscid Results Mach: Mach : NPR 8.78 NPR 1.4 (isentropic) (shock)

Turbulent Results Pressure Comparison Solver Study Mesh 3 vs Empirical NPR 1.4 NPR 2.0 Velocity NPR 2.0 NPR 3.0

References http://www.ivorbittle.co.uk/Books/Fluids%20boo 1. k/Chap[6pter%2013%20%20web%20docs/Chapte r%2013%20Part%203%20Complete%20doc.htm 2. http://www.engapplets.vt.edu/fluids/CDnozzle/cdi nfo.html Hunter, Craig A. “Experimental Investigation of 3. Separated Nozzle Flows.” Journal of Propulsion and Power No. 3 Vol. 20. (2004)