Accession Number : ADA138015
Title : Measurement of Hydroacoustic Particle Motion by Hot-Film Anemometry.
Descriptive Note : Memorandum rept.,
Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC
Personal Author(s) : Dubbelday, P S
PDF Url : ADA138015
Report Date : 10 Feb 1984
Pagination or Media Count : 59
Abstract : The parameter most often measured in acoustic fields is the pressure. Other scalar field variables, like the density or temperature, may be directly computed from the pressure fluctuations at one point. To determine the particle velocity vector, one needs to know the pressure in the neighborhood of a given point in order to derive the acceleration by numerically computing the gradient field of the pressure. One may measure the velocity field more directly by recording the effect of accelerators attached to a neutrally buoyant sphere that follows the particle motion more or less closely. Its sensitivity to velocity, therefore, will be inversely proportional to the frequency. Hot-film (or hot-wire) anemometry is based on the phenomenon that the heat transfer from an electrically heated film or wire is a function of the fluid motion past the sensor. It is extensively used in study of turbulence, where it is assumed that there is an exponential relation between heat flux and particle velocity, indicated as King's law. The importance of free convection implies a different mode of operation of the anemometer in horizontal or in vertical acoustic particle motion. In the first case the received frequency is twice that of the acoustic field, and the voltage is proportional to the square of the particle displacement. In the second case the frequency is equal to that of the field, and the voltage is linear in the particle displacement. The sensitivity and directional response may be increased by an imposed bias flow. This report describes the measurement of the anemometer output in horizontal and vertical particle motion for water and ethylene glycol.
Descriptors : *PARTICLE ACCELERATOR TECHNIQUES, HOT WIRE ANEMOMETERS, ACOUSTIC FIELDS, PRESSURE MEASUREMENT, HEAT TRANSFER, PARTICLE ACCELERATORS
Subject Categories : Test Facilities, Equipment and Methods
Distribution Statement : APPROVED FOR PUBLIC RELEASE