Improvement of turbulence estimation by Multi-Path sonic anemometry

Sonic anemometry is an established approach for turbulence measurement due to the absence of inertia in the sensor transfer function. On the other hand, the sound transducers and their mounting rods cause perturbations of the free flow, which can only be partially corrected, particularly regarding turbulence. The perturbations depend i.a. on the angle of attack to the measuring paths and the position of the mounting rods with respect to the flow direction. Therefore, the optimal sensor array geometry has been a subject of discussions for decades – and still is.

The concept of Multi-Path (MP) anemometry offers a way to realize different geometric approaches with one sensor head, enabling turbulence measurements by directly measured vertical wind components and/or vertical wind components derived from tilted paths. Depending on the free flow conditions, the optimal geometry can be dynamically selected.

For MP-sonics each sound transducer communicates with more than one partner, thus setting up more than one measuring path, in total nine measuring paths instead of three paths with only six transducers. On one hand the redundancy allows to analyze only subsets of data output, consequently the performance of conventional sonics can be simulated. On the other hand the MP concept allows multiple approaches to calculate turbulence parameters.

The benefits of the Multi-Path approach, especially in view of the heat flux, will be demonstrated by comparing results of field measurements with corresponding data from simulated conventional sonics.