{"id":157126,"date":"2022-06-06T08:32:46","date_gmt":"2022-06-06T08:32:46","guid":{"rendered":"\/knowledge\/forums\/topic\/in-fluent-why-is-the-speed-of-sound-property-required-for-materials-when-applying-udf-for-temperature-dependent-density-2\/"},"modified":"2023-07-31T12:36:41","modified_gmt":"2023-07-31T12:36:41","slug":"in-fluent-why-is-the-speed-of-sound-property-required-for-materials-when-applying-udf-for-temperature-dependent-density-2","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/in-fluent-why-is-the-speed-of-sound-property-required-for-materials-when-applying-udf-for-temperature-dependent-density-2\/","title":{"rendered":"In Fluent, why is the Speed of Sound property required for materials when applying UDF for temperature-dependent density?"},"content":{"rendered":"<p>When density is pressure-dependent, an extra term related to the speed of sound is needed in the pressure correction equation in order to stabilize the pressure solution for compressible flows.  Consequently, when density UDF is detected, Fluent automatically adds the Speed-of-Sound property input, as there is no way to distinguish whether the UDF will include a pressure dependency or not.  If the flow is incompressible (density a function of temperature only), you can simply set the Speed of Sound function to None<\/p>\n","protected":false},"template":"","class_list":["post-157126","topic","type-topic","status-publish","hentry","topic-tag-ansys-fluent","topic-tag-udf"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"When density is pressure-dependent, an extra term related to the speed of sound is needed in the pressure correction equation in order to stabilize the pressure solution for compressible flows. Consequently, when density UDF is detected, Fluent automatically adds the Speed-of-Sound property input, as there is no way to distinguish whether the UDF will include\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<link rel=\"canonical\" href=\"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/in-fluent-why-is-the-speed-of-sound-property-required-for-materials-when-applying-udf-for-temperature-dependent-density-2\/\" \/>\n\t<meta name=\"generator\" content=\"All in One SEO (AIOSEO) 4.9.10\" \/>\n\t\t<meta property=\"og:locale\" content=\"en_US\" \/>\n\t\t<meta property=\"og:site_name\" content=\"Ansys Knowledge | Ansys Innovation Space\" \/>\n\t\t<meta property=\"og:type\" content=\"article\" \/>\n\t\t<meta property=\"og:title\" content=\"In Fluent, why is the Speed of Sound property required for materials when applying UDF for temperature-dependent density? | Ansys Knowledge\" \/>\n\t\t<meta property=\"og:description\" content=\"When density is pressure-dependent, an extra term related to the speed of sound is needed in the pressure correction equation in order to stabilize the pressure solution for compressible flows. 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