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[FAQ]

When the high speed model is activated in CFX, the turbulent wall functions are calculated differently. This change affects the profile that is assumed for the non-dimensional near wall temperature (T+). CFX wall functions are designed for extremely high speed flows (Ma>3), so the near wall temperatures that are calculated may need to be blended with low speed values in instances where the flow speeds are considerably lower than Ma = 3 The warning indicates that the flow is in this regime. Sometimes, the high speed model is inappropriately set and should be deactivated. In other cases, the T+ error messages occur because the flow is still developing and will eventually disappear. The default setting for the recommended parameter, “highspeed wf mach threshold” is 0. At this value, the parameter instructs CFX to use high speed wall functions whenever the High Speed Model is active. Increasing the value of this parameter results in the use of a blended wall function. The near wall temperature calculation and the effects of flow velocity Can be found in the CFX Help Documentation at: // Theory Guide // 2. Turbulence and Wall Function Theory // 2.8. Modeling Flow Near the Wall // 2.8.1. Mathematical Formulation // 2.8.1.1. Scalable Wall Functions. There are no references to the expert parameter, but the underlying theory behind the high speed wall functions is described.