A thermal transient anemometer (TTA) is a device used to measure fluid flow over a planar cross-sectional area. The TTA system includes a frame containing several cells arranged in a grid and an electronic control unit. Each cell contains a sensing wire which provides an area- averaged velocity measurement. The measuring strategy relies on the transient convection and the temperature decay of the sensing wire, which is correlated with the magnitude of the velocity. The relationship between the temperature decay and the velocity is determined by calibrating the TTA with a set of known uniform velocities.The performance of the TTA under uniform and nonuniform flow conditions has been evaluated through numerical analysis and experimentation. Following the calibration of the TTA, a numerical model was developed to simulate the sensing wire in a TTA cell when ex- posed to a given velocity field. The model was used to investigate how linear velocity profiles affect the convective heat transfer and resulting temperature response of the sensing wire. Dimensionless velocity gradients ranging from 0 to 1.9 with corresponding mean velocities ranging from 0.1 to 15 m/s were evaluated. The temperature decay with velocity gradients exceeding 0.5 was slower than that of the uniform decay, due to strong axial conduction effects. This contributed to error in the mean velocity measurement from 1% with gradients of 0.4 to 24% with gradients of 1.9. A nonuniform flow correction scheme was developed using the numerical simulations that can reduce the mean velocity measurement error to within ±1% in the presence of large velocity gradients (2265 0.4). The correction scheme was validated by experimental measurements using the TTA. The TTA was used to evaluate the distribution of flow exiting an automotive radiator for various installation configurations. The correction scheme was utilized in the presence of strong velocity gradients.
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