Verification of CFD-based Computation of Thermal Comfort Indices

This study investigates the applicability of User-DefinedFunctions (UDFs) for determination of thermal comfort indices for non-uniform environments. The demand for such an investigation derived from the need to evaluate thermal environments in aircraft cabins in a more comprehensive way. It is normal practice by Airbus to determine the initial layout of ventilation systems also on the basis of computational fluid dynamics (CFD). The resulting set ups are subsequently tested in scale 1:1 cabin mock-ups that are basically life size cabin models. When airflow simulations for the A400M cargo hold were performed with CFD, thermal comfort was assessed in accordance with ISO 7730. The assessment of such environments was approached by computing the Predicted Mean Vote (PMV) and the Predicted Percentage of Dissatisfied (PPD) (Fanger, 1970). CFD-measurements in strongly nonuniform environments shall be conducted at several locations, at or around the subject to form average quantities (ISO 7726). The study compares indices based on CFD computed parameter quantities averaged over an area or a volume of cells near a human model to indices based on human subject votes. The CFD model offered reality equivalent airflow behavior confirmed by comparison with practical experiment data. The human subject votes derived from laboratory experiments conducted by P.O. Fanger. Surfaces that partly covered the human models were created for measuring the thermal comfort indices as well as single parameter values. Results with accuracy within +20/-10 percentage points PPD were achieved when no special precautions were taken. Measurements performed at surfaces placed 50 cm from the human models resulted in accuracies within ± 10 percentage points PPD. A proposed alternative solution, which involves a user-defined function that disregards human model induced radiant heat, yielded results with accuracy within ±5 percentage points PPD off target values for the optimal measuring distance to the human models.