{"id":462591,"date":"2026-08-13T10:22:05","date_gmt":"2026-08-13T10:22:05","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/maximum-pdf-table-enthalpy-exceeded-in-les-partially-premixed-fgm\/"},"modified":"2026-08-13T10:22:05","modified_gmt":"2026-08-13T10:22:05","slug":"maximum-pdf-table-enthalpy-exceeded-in-les-partially-premixed-fgm","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/maximum-pdf-table-enthalpy-exceeded-in-les-partially-premixed-fgm\/","title":{"rendered":"Maximum PDF Table Enthalpy Exceeded in LES + Partially Premixed FGM"},"content":{"rendered":"<p>I am running a transient LES combustion case in&nbsp;<strong>ANSYS Fluent 2022 R2<\/strong> and repeatedly receive the warning:<\/p>\n<p><code>Maximum PDF table enthalpy exceeded in XXXXX cells<\/code><\/p>\n<p>I would appreciate some guidance on whether this is mainly a PDF-table setup issue, a boundary-condition issue, or insufficient convergence within each time step.<\/p>\n<p>My setup is:<\/p>\n<ul>\n<li>\n<p>3D transient LES, WALE SGS model<\/p>\n<\/li>\n<li>\n<p>Partially Premixed Combustion<\/p>\n<\/li>\n<li>\n<p>Flamelet Generated Manifold<\/p>\n<\/li>\n<li>\n<p>C-Equation<\/p>\n<\/li>\n<li>\n<p>Turbulence-Chemistry Interaction: <strong>Finite-Rate<\/strong><\/p>\n<\/li>\n<li>\n<p>Premixed flamelets generated <strong>adiabatically<\/strong><\/p>\n<\/li>\n<li>\n<p>CFD Energy Treatment: <strong>Non-Adiabatic<\/strong><\/p>\n<\/li>\n<li>\n<p>No TFM, EDC, or finite-rate species chemistry in the 3D CFD domain<\/p>\n<\/li>\n<\/ul>\n<p>The physical configuration is a premixed CH4-air jet discharging into ambient air. In the Fluent FGM two-stream definition:<\/p>\n<ul>\n<li>\n<p>(Z=1): premixed CH4-air mixture at (phi=0.8), 300 K<\/p>\n<\/li>\n<li>\n<p>(Z=0): air at 300 K<\/p>\n<\/li>\n<li>\n<p>Main inlet: (Z=1, c=0)<\/p>\n<\/li>\n<li>\n<p>Ambient pressure boundaries\/backflow: (Z=0, c=0, T=300) K<\/p>\n<\/li>\n<\/ul>\n<p>The flame is ignited\/stabilized using an annular pilot mass-flow inlet. For numerical simplicity, I prescribe the pilot as already-burnt products:<\/p>\n<ul>\n<li>\n<p>(Z=1)<\/p>\n<\/li>\n<li>\n<p>(c=1)<\/p>\n<\/li>\n<li>\n<p>currently (T=2001) K<\/p>\n<\/li>\n<\/ul>\n<p>Initially I used 2230 K, but this produced stronger local temperature\/enthalpy overshoots near the pilot, so I reduced it to approximately the adiabatic burnt temperature of the (phi=0.8) mixture.<\/p>\n<p>The pilot mass flow was originally 13% of the main inlet flow. With hot burnt products, the pilot inlet velocity is about 3.91 m\/s. I have also tested lower pilot flow rates.<\/p>\n<p>The non-adiabatic PDF table display shows a maximum temperature of approximately <strong>2425 K<\/strong> at the upper enthalpy range. During the CFD solution, the cells exceeding the maximum PDF-table enthalpy are mainly associated with the hot flame\/pilot region. The maximum CFD temperature also occasionally approaches approximately 2425 K.<\/p>\n<p>The warning count is sensitive to the transient convergence settings. For example, reducing maximum iterations per time step from 25 to 20 caused both residuals and the number of affected cells to increase substantially.&nbsp;<\/p>\n<p>Most residuals behave reasonably, although continuity remains relatively high compared with the other equations.<\/p>\n<p>There is some reverse flow at the upper pressure outlet, but the magnitude is very small: approximately -0.004 m\/s minimum velocity. Backflow temperature and composition are correctly specified as 300 K air.<\/p>\n<p>My main questions are:<\/p>\n<ol>\n<li>\n<p>Is it correct to generate <strong>adiabatic FGM flamelets<\/strong> and then use <strong>Non-Adiabatic Energy Treatment<\/strong> in the CFD solution in this way?<\/p>\n<\/li>\n<li>\n<p>Does <code>Maximum PDF table enthalpy exceeded<\/code> usually indicate that the PDF enthalpy range itself is insufficient, or can under-converged transient time steps create the same warning?<\/p>\n<\/li>\n<li>\n<p>Could prescribing the pilot directly as hot burnt products ((c=1, Tapprox2000) K) cause this problem, even though its temperature is below the maximum temperature visible in the PDF table?<\/p>\n<\/li>\n<li>\n<p>Is the relevant upper enthalpy limit dependent on local (Z) and (c), rather than simply on the global maximum temperature shown in <code>Display PDF Table<\/code>?<\/p>\n<\/li>\n<li>\n<p>What is the recommended way in Fluent to identify exactly where and why the cells exceed the PDF-table enthalpy range?<\/p>\n<\/li>\n<li>\n<p>Before rebuilding the PDF table with a larger enthalpy range, what settings or fields should I check first?<\/p>\n<\/li>\n<\/ol>\n<p>I would prefer to identify the root cause before simply extending the table range, since I do not want to hide a numerical or boundary-condition problem by increasing the table limits.<\/p>\n","protected":false},"template":"","class_list":["post-462591","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 am running a transient LES combustion case in ANSYS Fluent 2022 R2 and repeatedly receive the warning: Maximum PDF table enthalpy exceeded in XXXXX cells I would appreciate some guidance on whether this is mainly a PDF-table setup issue, a boundary-condition issue, or insufficient convergence within each time step. 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