{"id":390486,"date":"2024-10-19T10:45:00","date_gmt":"2024-10-19T10:45:00","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/unexpected-downward-trend-in-turb-intensity-using-variable-k-and-in-fluent\/"},"modified":"2024-10-19T10:45:00","modified_gmt":"2024-10-19T10:45:00","slug":"unexpected-downward-trend-in-turb-intensity-using-variable-k-and-in-fluent","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/unexpected-downward-trend-in-turb-intensity-using-variable-k-and-in-fluent\/","title":{"rendered":"Unexpected Downward Trend in Turb. Intensity Using Variable k and \u03b5 in Fluent"},"content":{"rendered":"<p>&lt;p&gt;Hello,&lt;\/p&gt;&lt;p&gt;I&#8217;m running a simulation with a <strong>Reynolds number of 100,000<\/strong> and encountering an issue with the expected variation of <strong>turbulence intensity (TI)<\/strong>. I&rsquo;m using a <strong>Realizable k-&epsilon; turbulence model<\/strong> with variable <strong>turbulent kinetic energy (k)<\/strong> and <strong>dissipation rate (&epsilon;)<\/strong>, controlled via a UDF. My setup includes:&lt;\/p&gt;<\/p>\n<ul>\n<li><strong>Reynolds number<\/strong>: 100,000<\/li>\n<li><strong>Turbulence model<\/strong>: Realizable k-&epsilon; with Menter-Lechner wall treatment<\/li>\n<li><strong>Time steps<\/strong>: 150, each with a 0.1 s step size<\/li>\n<li><strong>Velocity<\/strong>: 1.46 m\/s, leading to the specified Reynolds number<\/li>\n<\/ul>\n<p>&lt;p&gt;The issue is that, when calculating the TI based on the fluctuating values of <strong>k<\/strong> and <strong>&epsilon;<\/strong>, I am expecting an upward variation in the TI values over time. However, the actual trend I am observing is <strong>downward<\/strong>. This was quite unexpected, and I was hoping to gain insight into why this might be happening.&lt;\/p&gt;&lt;p&gt;Has anyone encountered similar behavior in Fluent or has any thoughts on why the trend could be downward? Is there something I could be missing in my UDF or in how Fluent handles the turbulence variables over time?&lt;\/p&gt;&lt;p&gt;Any insights or suggestions would be greatly appreciated!&lt;\/p&gt;&lt;p&gt;Thank you.&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-390486","topic","type-topic","status-publish","hentry","topic-tag-fluent-ansys-1","topic-tag-cfd-udf-fleunt","topic-tag-turbulence-intensity"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello,I&#039;m running a simulation with a Reynolds number of 100,000 and encountering an issue with the expected variation of turbulence intensity (TI). 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