Simultaneous and well-resolved velocity and temperature measurements in the Atmospheric Surface Layer

A robust and scalable nano-scale hot- and cold-wire system was constructed and deployed at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility on the playa of western Utah as part of the Idealized Planar Array experiment for Quantifying Surface heterogeneity or IPAQS2018 experiment. Developed and manufactured in-house at Princeton University using standard MEMS (Micro Electro-Mechanical Systems) techniques, Nano-Scale Thermal Anemometry Probes (NSTAPs) were used in this experiment to capture single-component velocity data in the atmospheric surface layer. The small size of the NSTAP results in a spatial resolution three orders of magnitude greater than conventional sonic anemometers and ten times greater than conventional hot-wires. Its small size and silicon support structure also contribute to its high survival rate in the severe field environment. Although constant temperature anemometry (CTA) hot-wire systems offer greater ease of use, they are not economically feasible for applications demanding multiple sensors. The cheaper, alternative constant current anemometry (CCA) mode of operation comes at the cost of reduced bandwidth and higher sensitivity to temperature fluctuations that alter the heat transfer relations. This setup addresses both of these drawbacks to render CCA a viable option in the atmospheric surface layer. The small size of the NSTAP enables CCA measurements with a bandwidth of 10 kHz, and to account for the drastic temperature changes that occur, the temperature variant of the NSTAP, the TNSTAP, is mounted adjacent to each NSTAP. Simultaneous sampling of well-resolved temperature and velocity data then allows for an instantaneous application of the temperature compensation scheme proposed by Hultmark and Smits (2010), which can be used in both CTA and CCA mode.

Funded by the National Science Foundation (AGS-1649049)

Hultmark, M. and Smits, A. J., "Temperature corrections for constant temperature and constant current hot-wire anemometers", Meas. Sci. Technol. Vol. 21, 105404, 2010.