{"id":397310,"date":"2024-12-12T17:09:45","date_gmt":"2024-12-12T17:09:45","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/stability-and-convergence-of-3d-ejector-simulations\/"},"modified":"2024-12-12T17:09:45","modified_gmt":"2024-12-12T17:09:45","slug":"stability-and-convergence-of-3d-ejector-simulations","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/stability-and-convergence-of-3d-ejector-simulations\/","title":{"rendered":"Stability and Convergence of 3D Ejector Simulations"},"content":{"rendered":"<p>&lt;p&gt;I&#8217;m trying to simulate a simple gas ejector, only several inches in size, with ideal gas air (constant properties) using geometry and conditions from a disseration I&#8217;ve found online. The author simplified his domain to 2D axisymmetric. My plan is to use his design as a starting point for an alternative design I&#8217;m working on that will require the domain be 3D, so I&#8217;m trying to replicate the author&#8217;s results in 3D to act as a benchmark for the alternative design. From my own past experience, modeling a simple gas ejector has been confusingly difficult to converge in the density-based solver. Below is the geometry and settings of the simple replication case that I&#8217;m currently trying to run:&lt;\/p&gt;&lt;p&gt;&nbsp; <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734020392-mceclip0.png\" width=\"425\" height=\"289\" \/> <img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734020633-mceclip1.png\" \/>&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Mesh&lt;\/span&gt;:&lt;\/p&gt;<\/p>\n<ul>\n<li>Polyhedral<\/li>\n<li>Body Sizing is 0.02 inches<\/li>\n<li>Body of Influence is 0.005 inches<\/li>\n<li>Curvature Normal Angle is 10 degress<\/li>\n<li>Boundary Layer is Smooth Transition with 5 layers, Transition Ratio of 0.272, and a Growth Rate of 1.5<\/li>\n<li>Minimum Orthogonal Quality is 0.5<\/li>\n<li>Cell count is 360,771 cells<\/li>\n<\/ul>\n<p>&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Model Settings&lt;\/span&gt;:&nbsp;&lt;\/p&gt;<\/p>\n<ul>\n<li>Density-Based Solver<\/li>\n<li>K-Epsilon Realizable with Enhanced Wall treatment and Production Limiter<\/li>\n<li>Formulation is Implicit with a Courant Number of 5<\/li>\n<li>All Discretizations set to Second Order Upwind<\/li>\n<li>Gradient is Green-Gauss Node Based<\/li>\n<li>Flux Type is Roe-FDS<\/li>\n<li>Enabled High Speed Numerics, Warped-Face Gradient Correction, and Convergence Acceleration for Stretched Meshes (CASM is probably unnecessary)<\/li>\n<li>Under-Relaxtion Factors left at default values<\/li>\n<li>All Residuals set to 1e-6<\/li>\n<\/ul>\n<p>&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Boundary Conditions&lt;\/span&gt;:&lt;\/p&gt;<\/p>\n<ul>\n<li>Operating Pressure is 0 psi<\/li>\n<li>Primary Inlet: Total Pressure is 164.7 psi, Supersonic\/Initial Gauge Pressure is 164 psi, and Total Temperature is 300 K<\/li>\n<li>Secondary Inlet: Total Pressure is 59.3 psi, Supersonic\/Initial Gauge Pressure is 59 psi, and Total Temperature is 300 K<\/li>\n<li>Outlet: Gauge Pressure (Static Pressure) is 59.7 psi, Backflow Total Temperature is 300 K<\/li>\n<\/ul>\n<p>&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Residuals and Entrainment Ratio Plots&lt;\/span&gt;:&lt;\/p&gt;&lt;p&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734021792-mceclip2.png\" width=\"681\" height=\"414\" \/> <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734021840-mceclip3.png\" width=\"700\" height=\"413\" \/>&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Mach Number and Static Pressure Contours&lt;\/span&gt;:&lt;\/p&gt;&lt;p&gt;&nbsp;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734022114-mceclip6.png\" width=\"736\" height=\"312\" \/><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734022074-mceclip5.png\" width=\"732\" height=\"313\" \/>&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;Vector Plot&lt;\/span&gt;:&lt;\/p&gt;&lt;p&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734022284-mceclip7.png\" width=\"828\" height=\"392\" \/> <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734022483-mceclip8.png\" width=\"880\" height=\"393\" \/>&lt;\/p&gt;&lt;p&gt;As shown in the Residuals and Entrainment Ratio plots, I had decently low convergence but not all the way to 1e-6. My Entrainment Ratio plot is oscillating, and you can even see in the Vector plot at the diffuser exit that I had slight backflow. These results were actually some of the better quality that I&#8217;ve obtained so far. I&#8217;ve also found that a Poly-Hexcore mesh for some reason performs slightly worse than a Polyhedral mesh of equal size. Any advice on what more I need incorporate or change to acheive complete convergence of a simple 3D ideal gas ejector? Information online of 3D ejector CFD is scarce.&lt;\/p&gt;&lt;p&gt;Thanks in advance.&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-397310","topic","type-topic","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"I&#039;m trying to simulate a simple gas ejector, only several inches in size, with ideal gas air (constant properties) using geometry and conditions from a disseration I&#039;ve found online. 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