{"id":461448,"date":"2026-07-17T13:43:23","date_gmt":"2026-07-17T13:43:23","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fgm-flamelets-in-les\/"},"modified":"2026-07-17T13:43:23","modified_gmt":"2026-07-17T13:43:23","slug":"fgm-flamelets-in-les","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fgm-flamelets-in-les\/","title":{"rendered":"FGM Flamelets in LES"},"content":{"rendered":"

<p class=”PDq2pG_selectionAnchorContainer” data-start=”125″ data-end=”131″>Hello,<\/p><p data-start=”133″ data-end=”289″>I am setting up a transient LES combustion simulation in Ansys Fluent 2021 R2 and would appreciate clarification regarding the two nonadiabatic FGM options.<\/p><p data-start=”291″ data-end=”311″>My current setup is:<\/p><ul data-start=”313″ data-end=”685″><li data-section-id=”acsmq5″ data-start=”313″ data-end=”344″>Partially Premixed Combustion<\/li>\n

<li data-section-id=”1ysa6wq” data-start=”345″ data-end=”357″>C-Equation<\/li>\n

<li data-section-id=”1dbz2dv” data-start=”358″ data-end=”387″>Flamelet Generated Manifold<\/li>\n

<li data-section-id=”2v8u30″ data-start=”388″ data-end=”407″>Premixed Flamelet<\/li>\n

<li data-section-id=”13w4xbq” data-start=”408″ data-end=”432″>CHEMKIN Physical Space<\/li>\n

<li data-section-id=”pzjyfj” data-start=”433″ data-end=”448″>LES with WALE<\/li>\n

<li data-section-id=”1ewbbzh” data-start=”449″ data-end=”490″>Natural gas–air mixture at <span class=”katex”><span class=”katex-mathml”>\u03d5=0.8\\phi=0.8<\/span><span class=”katex-html” aria-hidden=”true”><span class=”base”><span class=”mord mathnormal”>\u03d5<\/span><span class=”mrel”>=<\/span><\/span><span class=”mord”>0.8<\/span><\/span><\/span><\/li>\n

<li data-section-id=”g5i55d” data-start=”491″ data-end=”540″>Fuel and oxidizer reference temperatures: 300 K<\/li>\n

<li data-section-id=”1grrs0u” data-start=”541″ data-end=”558″>Pressure: 1 atm<\/li>\n

<li data-section-id=”2uadxk” data-start=”559″ data-end=”594″>Open-atmosphere Bunsen-type flame<\/li>\n

<li data-section-id=”ys7iu3″ data-start=”595″ data-end=”615″>Radiation disabled<\/li>\n

<li data-section-id=”tgv97l” data-start=”616″ data-end=”650″>Conjugate heat transfer disabled<\/li>\n

<li data-section-id=”4hzz0l” data-start=”651″ data-end=”685″>Solid walls treated as adiabatic<\/li>\n<\/ul>\n

<p data-start=”687″ data-end=”828″>The production mesh contains approximately 5–8 million cells. Flamelet and PDF-table generation is performed separately on a small test mesh.<\/p><p class=”” data-start=”830″ data-end=”1158″>My primary interest is the accuracy of the transient temperature field, particularly the temporal evolution of temperature at selected monitoring locations. Emissions prediction is not part of the present study.<\/p><p data-start=”1160″ data-end=”1254″>I am trying to understand the practical difference between the following three configurations:<\/p><p data-start=”1160″ data-end=”1254″> <\/p><div class=”relative w-full mt-4 mb-1″><div class=””><div class=”contents”><div class=”relative”><div class=”h-full min-h-0 min-w-0″><div class=”h-full min-h-0 min-w-0″><div class=”border border-token-border-light border-radius-3xl corner-superellipse\/1.1 rounded-3xl”><div class=”h-full w-full border-radius-3xl bg-(–code-block-surface) corner-superellipse\/1.1 overflow-clip rounded-3xl [–code-block-surface:var(–bg-elevated-secondary)] dark:[–code-block-surface:var(–composer-surface-primary)] lxnfua_clipPathFallback”><div><div><div><div id=”code-block-viewer” dir=”ltr”><div><\/p>\n

1. Energy Treatment: Adiabatic\n\n2. Energy Treatment: Non-Adiabatic\n   Nonadiabatic Flamelets: OFF\n\n3. Energy Treatment: Non-Adiabatic\n   Nonadiabatic Flamelets: ON<\/pre>\n
<\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div><div class=””><div class=””> <\/div><\/div><\/div><\/div><\/div><\/div><p data-start=”1433″ data-end=”1708″>My understanding is that in the second configuration, Fluent solves enthalpy transport and includes enthalpy as a PDF-table coordinate, but the nonadiabatic PDF is constructed from adiabatic flamelets under the assumption that species composition is independent of heat loss.<\/p><p data-start=”1710″ data-end=”1947″>When <code data-start=”1715″ data-end=”1739″>Nonadiabatic Flamelets<\/code> is enabled, flamelets are additionally solved for different fuel and oxidizer enthalpy levels, so species composition, reaction-progress source terms and laminar flame properties may also depend on enthalpy.<\/p><p data-start=”1949″ data-end=”2019″>I would particularly appreciate clarification on the following points:<\/p><\/p>\n
    <li data-section-id=”1bii1cs” data-start=”2021″ data-end=”2274″>For a case with no radiation, no CHT, adiabatic walls and equal 300 K inlet temperatures, how much difference should normally be expected between a fully adiabatic FGM calculation and a nonadiabatic calculation with <code data-start=”2240″ data-end=”2264″>Nonadiabatic Flamelets<\/code> disabled?<\/li>\n
    <li data-section-id=”khdrt6″ data-start=”2276″ data-end=”2518″>Does entrainment and mixing with 300 K ambient air provide any physical reason to use the nonadiabatic formulation, or is this cooling already represented through mixture-fraction and progress-variable variation in the adiabatic FGM table?<\/li>\n
    <li data-section-id=”1mh9pay” data-start=”2520″ data-end=”2724″>For accurate time-resolved temperature histories and flame-crossing durations, can <code data-start=”2606″ data-end=”2635″>Nonadiabatic Flamelets = ON<\/code> materially improve the result when there is no significant external heat-loss mechanism?<\/li>\n
    <li data-section-id=”drgx7″ data-start=”2726″ data-end=”2919″>Is the main benefit of enabling nonadiabatic flamelets limited to cases involving large wall heat losses, radiation, quenching, different inlet temperatures or temperature-sensitive species?<\/li>\n
    <li data-section-id=”1qk2zv5″ data-start=”2921″ data-end=”3272″>What is the approximate computational impact of enabling <code data-start=”2981″ data-end=”3005″>Nonadiabatic Flamelets<\/code>?<ul data-start=”3011″ data-end=”3272″><li data-section-id=”e11k6j” data-start=”3011″ data-end=”3051″>Increase in flamelet-generation time<\/li>\n
    <li data-section-id=”1fe1c0p” data-start=”3055″ data-end=”3096″>Increase in PDF-table generation time<\/li>\n
    <li data-section-id=”lp3r9l” data-start=”3100″ data-end=”3132″>Increase in PDF\/table memory<\/li>\n
    <li data-section-id=”awb38b” data-start=”3136″ data-end=”3181″>Increase in RAM usage during the main LES<\/li>\n
    <li data-section-id=”nhsvgx” data-start=”3185″ data-end=”3272″>Increase in wall-clock time per timestep after the table has already been generated<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n
    <p data-start=”3274″ data-end=”3573″>I understand that the exact cost depends on the grid dimensions and number of stored species, but even a qualitative estimate or typical range would be helpful. In particular, does enabling this option mainly affect preprocessing, or can it noticeably increase the runtime of a 5–8 million-cell LES?<\/p><p data-start=”3575″ data-end=”3895″>In later stages, I also plan to repeat the analysis with approximately 10% and 20% hydrogen addition. Would hydrogen addition by itself make nonadiabatic flamelet generation more important for accurate temperature and flame-crossing predictions, even when radiation, CHT and nonadiabatic wall conditions remain disabled?<\/p><p data-start=”3897″ data-end=”4053″>My current concern is choosing the least expensive model that still provides reliable instantaneous temperature evolution rather than emissions such as NOx.<\/p><p data-start=”3897″ data-end=”4053″>Its a little bit long but I hope you can help. <\/p><\/p>\n","protected":false},"template":"","class_list":["post-461448","topic","type-topic","status-publish","hentry","topic-tag-cfd-combustion","topic-tag-fgm","topic-tag-flamelet-1","topic-tag-les"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27792"],"_bbp_topic_id":["461448"],"_bbp_subscription":["553792"],"_bbp_author_ip":["144.122.196.8"],"_bbp_last_reply_id":["0"],"_bbp_last_active_id":["461448"],"_bbp_last_active_time":["2026-07-17 13:43:23"],"_bbp_reply_count":["0"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["1"],"_bbp_engagement":["553792"],"_btv_view_count":["25"],"_bbp_topic_status":["unanswered"]},"test":"can-sumeyyemetu-edu-tr"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/461448","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/461448\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=461448"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}