Accurate wall positioning of the hot-wire sensor using a high aspect-ratio rectangular nozzle

Accurate measurement of wire distance from the wall is vital especially during hot-wire (HW) anemometry of the boundary layer flows. In such flows the length scales are comparable to the diameter of the sensor and there are large gradients of flow properties near the wall. Thus, the accuracy of calculating the wall dependence parameters from the hot-wire experimental data is strongly dependent on the accuracy of the wire positioning technique. Advanced graduated microscopes, digital camera systems, utilization of electro/mechanical probe stops, using of the wall-effects of the HW sensors and finally laser based devices are known methods for initial positioning of HW sensors. In this paper, the flow characteristics of a high-aspect-ratio (HAR) rectangular nozzle are used as a main base for proposing a new method for initial wire positioning. For validating of the method, the characteristics of jet flow from HAR rectangular nozzles and behaviors of some flat plate transitional boundary layers are studied experimentally. Comparisons show that high accuracy, easy performing and low-cost equipments are main characteristics of the proposed method. It is immediately applicable for researchers using hot-wire anemometry in boundary layer flows over both of electrically conductive and non-conductive test surfaces.

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► Accurate wall positioning of the hot-wire sensors.
► Flow characteristics of a high-aspect-ratio (HAR) rectangular nozzle are used for proposing a new method for initial wire positioning of hot-wire probes.
► It is validated via investigation of the skin friction coefficients of some transitional boundary layer flows using hot wire anemometry.
► High accuracy, easy operability and low-cost equipments are the main characteristics of the proposed method.
► It can be used for both cases of electrically conductive and non-conductive test surfaces using hot-wire anemometry.