Hot-wire anemometry (HWA) remains an essential diagnostic tool for high–frequency velocity measurements in aerodynamic research, yet its practical accuracy strongly depends on robust temperature correction and reliable multi–component probe calibration. Despite the maturity of the technique, the literature provides no consensus on how best to correct for fluid–temperature variations or how to calibrate X-wire probes with consistent accuracy across wide velocity and angular ranges. The situation is further complicated at the TU Delft Low-Speed Wind Tunnel Laboratory (LSL), where the absence of an in-situ multi-wire calibration system has made efficient and repeatable probe preparation difficult. This thesis addresses these issues by developing a new automated calibration framework for multi-wire CTA probes and performing a comprehensive evaluation of existing temperature-correction and X-wire calibration schemes.
The first part of the work concerns the separation of velocity and temperature effects in CTA measurements. Six temperature-correction models—ranging from simple Bearman [1]-type scaling ignoring the change in fluid properties with temperature, to more complex formulations incorporating fluid-property variations and the Collis & Williams factor [2] are applied to four independent datasets from literature, covering a wide range of velocities and temperature conditions. Each model is assessed by collapsing data acquired at varying temperatures onto a single fourth-degree polynomial calibration curve to quantify the residual error via normalized root mean square percentage error. Across all datasets, simple temperature corrections perform surprisingly well. Relying on resistance-based wire-temperature estimation suffers from uncertainty, with the best success when calculating the fluid properties at the film temperature and applying the Collis & Williams correction. Allowing the wire temperature to act as an optimization parameter can improve the fit of the curves, confirming earlier findings that resistance-derived temperatures can introduce systematic error.
The second part of the thesis focuses on the calibration of X-wires. A new miniature, high-precision, in-situ yaw calibrator is designed and implemented. The device integrates a compact high-torque servo motor and a magnetic rotary encoder with high accuracy, assembled using high-precision alignment procedures. With the calibration and controlled through a LabView interface, and the position feedback and servo control integrated via an Arduino implementation, the system enables automated yaw sweeps. Its compact form factor allows installation directly inside restricted windtunnel test sections.
Using this system, a dense X-wire calibration dataset was collected, spanning velocities from 5 to 30ms−1 in 1ms−1 increments and yaw angles from −40◦ to 40◦ in 1◦ steps. The dataset enabled comparison of calibration schemes, including interpolation-based indirect methods (Lueptow [3] and Tropea [4] variants), and direct polynomial surface