Development of an experimental apparatus for flat plate drag measurements and considerations for such measurements

Accurately measuring small changes in aerodynamic drag over a flat surface stands at the core of the development of technologies capable of reducing turbulent friction drag. A wind tunnel drag measurement system was developed which improves significantly on the state of the art. Experimental tests demonstrated that an uncertainty of less than 0.5% of C ( D ) at a 95% confidence level was typically achieved, already at drag values below 1 N. This was replicated in two different wind tunnels. A match with literature on riblet performance within 1% of C ( D ) was obtained. A crucial aspect of the design is the implementation of a correction for the pressure forces on the streamwise-facing surfaces of the test plate assembly. The flexible architecture of the system in the present realisation makes it suitable for most wind tunnels having a test section width of 400 mm or larger, which allows for accelerated development of turbulent drag reduction concepts from moderate-size low-cost facilities towards flow conditions relevant to the intended industrial application.

Automated summary

A wind tunnel drag measurement system has been developed in this study to accurately measure small changes in aerodynamic drag over a flat surface. Experimental tests show that the system achieves high accuracy in different wind tunnels and matches the results from related literature. The flexible structure of this system enables it to be used in most wind tunnels, accelerating the research and development of turbulent drag reduction concepts.