On Velocity Measurements in Non-Isothermal Turbulent Flows

Turbulent velocity measurements in non-isothermal flows are conventionally performed by constant current hot-wire anemometry. The procedure involved however is cumbersome, the output signals are nonlinear and more critically a continuous signal of velocity fluctuations is not provided. The method described here utilizes two orthogonal wires situated a fraction of a millimeter apart. The upstream wire is operated in a low overheat, constant-current compensated mode thus providing a signal proportional to temperature while the down-stream wire, practically unaffected by the thermal wake of the first wire is operated in the constant temperature mode. Compensation for the effects of local temperature on the downstream wire is accomplished by the temperature signal obtained from the first wire. Variations of Kramers\u27 law coefficients (both being functions of density and thermal conductivities) due to temperature variations are compensated through an analog circuit at the input of the logarithmic amplifiers of the linearizer. By this method, linear and separate signals of the velocity and local temperature are thus obtained simultaneously and continuously. Advantages accruing from this method are readily adapted to cross-wire configuration thus permitting direct measurements of momentum and heat transfer in turbulent heated flows