THE DEVELOPMENT OF A PULSED MULTIELEMENT HOT-WIRE ANEMOMETER

This paper describes the development of a pulsed hot-wire anemometer which lends itself to multiple-element applications. Unlike previous pulsed anemometers which have separate heating and sending wires, the methods described here utilize a single wire as both heater and sensor. It is shown that the transient heating and cooling characteristics of such an element are a function of the local convection rate and hence the local fluid velocity. Thus, if the heating current is supplied in short duration pulses and the time taken to reach a given set temperature (the set temperature point) is recorded, then velocity information is acquired as time values rather than the voltages or currents expected from conventional systems. As a single-point measurement can be completed in a relatively short time, the system allows access to hundreds of elements per second. As the current is discontinuous, a relatively high value can be used, so giving signal processing advantages over conventional systems. After reviewing the relevant theory and discussing the significance of the system parameters, two operational methods of application of the anemometer are developed. A representative application example, that of the quantification of flow round a cylinder, is described and results given.