Development and characterization of a probe to measure scalar transport

The present study describes a newly developed sensor capable of simultaneously measuring fine-scale velocity and concentration gradients in a 4.8 × 6 × 4 mm 3 volume. The sensor combines the established technologies of photoionization, to obtain concentration, and hot-wire (x-array) anemometry, to obtain two components of the velocity vector. Spatial gradients are obtained by finite difference across the measurement volume. A novelty of the sensor lies in the ability to capture instantaneous time series of most of the terms in the scalar variance transport equation. The frequency response of the sensor is approximately 325 Hz for concentration and 1.2 kHz for velocity. The present study focuses primarily on the development and characterization of the probe. Major sources of measurement uncertainty are discussed, including instrumentation noise, calibration errors, flow distortion and spatiotemporal resolution. The propagation of uncertainty, relevant to the terms in the scalar variance transport equation, is also briefly discussed.