Thin film gauges for fluctuating velocity measurements in blood

Abstract

The frequency response has been determined for two probe designs used for cardiovascular measurements: one conical, the other cylindrical. The frequency range was 1-1000 Hz using an oscillatory velocity component superimposed on a mean flow; the test fluid was water. The amplitude response to the fluctuating component was found to depend on the Strouhal number (a normalized frequency) and was almost independent of the amplitude of oscillation. At small Strouhal numbers the behaviour is quasi-steady; at higher values the sensitivity progressively diminishes, but for the cylindrical probe there is an intermediate region of increased sensitivity. The oscillatory component had no effect upon the conical probe sensitivity to the mean velocity, whereas the cylindrical probe showed an increasing apparent mean velocity for some conditions. Fluctuating velocity values were inferred from steady flow calibration data and, therefore, a detailed comparison was made between such calibrations in blood and water.