Contribution of CFD simulation on the design and characterization of a wind tunnel for air leakage measurements

Building airtightness evaluation is crucial for reducing infiltration and improving building energy efficiency. Many countries now mandate air leakage measurements during building commissioning. However, the uncertainty of these measurements, particularly due to wind speed influence, has become a key concern. Wind tunnel testing allows for the assessment of wind impact on the uncertainty of airtightness measurements.

In this context, this contribution illustrates the benefits of combining CFD with wind tunnel testing to support wind tunnel design, measurements, and result interpretation.

Firstly, CFD simulations are employed to verify the proper scaling of an aerodynamic wind tunnel in which a reduced scale building designed for air leakage measurements is placed. CFD simulation is also used to verify the flow and pressure field similarity between the full-scale building and the reduced scale building. The results show that the wind tunnel is suitable for evaluating pressure loads on the windward and leeward faces of an isolated building but has limitations in characterizing the full leeward airflow due to the insufficient length of the test chamber relative to the length of the reduced scale building.

CFD simulations are then used to characterize the velocity and pressure fields both in the empty wind tunnel and in the wind tunnel with the reduced scale building. The comparison of wind tunnel measurements and CFD simulation results shows good agreement of mean pressure coefficients on the windward and leeward facades, consistent with values from full-scale experiments. This confirms the applicability of this wind tunnel for air leakage measurements under steady wind conditions.

Finally, CFD simulation is performed to design a wind tunnel extension for a complete characterization of the downstream flow of the reduced scale building and for the addition of roughness elements to reproduce outdoor wind velocity and turbulence intensity profile