Description of a 1000 Sensor Constant Current Anemometer System for Locating Three-Dimensional Turbulent Boundary Layer Separations.

摘要

The location of three-dimensional separation on bodies such as submarines is important diagnostic information. Considerable changes in the side forces and moments occur with the undesirable phenomenon of separation. Three-dimensional flow separations occur very close to local minima in the magnitude of the wall shear stress. A 1000-flush-surface-sensor constant-current-anemometer separation location system is described here for locating these local minima along the axis of a body. As shown here, the convective heat transfer coefficient from a sensor is proportional to the one-third power of the local skin friction magnitude for the directionally-insensitive sensors described here. The constant-current anemometer design permits the use of strips of serially-connected sensors that require only one current source per strip. These compact electronics can be housed inside the body. The voltage drop across each sensor is measured for a number of different computer-controlled currents and related to the local heat transfer coefficient and the fixed parameters for that sensor. Each sensor mounted on the body forms a first order dynamic thermal system whose time constants can be experimentally determined. Thereafter, such as in transient flow separation conditions, measurements only for one current axe necessary for a given precalibrated sensor. Results are presented for two sets of tests: (1) flow in the VPI and SU Water Tunnel over a 20 deg angle-of-attack circular cylinder and (2) a 6:1 prolate spheroid at 15 deg angle of attack towed in the David Taylor Research Center 140' Basin. The separation location results are in close agreement with those from earlier wind tunnel tests by other investigators.