A Three Component Drag Probe for the Measurement of Turbulent Water Velocity Fluctuations

Two spherical drag probes which use variable inductance devices as displacement transducers were built to measure turbulent water velocity fluctuations. The associated circuitry provides voltage outputs which are proportional to the three components of force acting on the spherical sensor of each probe. The probes respond to the fluid drag force and also to the fluid inertial force in an accelerating flow field. The frequency at which the response is 3 dB down is 18 Hz for one probe and 41 Hz for the other. The instruments have been calibrated for oscillating flows with velocities from 10 to 150 cm/sec.