Measurement of Hydrodynamic Forces and Moments and Flow Field Mapping of a Model in Coning Motion
Abstract
A method of captive model testing using an axisymmetric marine vehicle model in steady motion with constant roll and yaw rates has been used experimentally to obtain functional relationships between certain motion parameters and the resultant hydrodynamic forces and moments on the body. Specifically, cross coupling terms in roll rate and yaw rate have been investigated for non-planar cross-flow. An instrumented slender body of revolution with length/diameter of 9.5 was tested at Reynolds number of about 5 million, based on length. The tests were conducted at free stream velocity of 25 ft/s for coning angles between zero and -20 deg in 2 deg increments, at rotation rates of up to 200 rpm in 12.5 rpm increments in both rotational directions. The character of force and moment terms varying with rotation rate and coning angle was determined. The results may be translated to functional relationships between the hydrodynamic coefficients and the angular velocities in roll and yaw. The data showed a transition in the forms of the sway force and the pitch moment after the coning angle exceeded -10 deg., due to body lift in the cross flow. A method for measuring the velocity field about the model using laser doppler velocimetry has been developed. The flow field was mapped for two model coning angles at one moderate rotation rate. The flow field representation portrays perturbations in cross flow velocity at five sections in a body-fixed reference frame. This method is useful in understanding the vortex mechanisms at work to influence body forces and moments. The data showed formation of asymmetric body vortices after the coning angle exceeded -10 deg. (jhd)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1990
- Accession Number
- ADA226684
Entities
People
- Thomas J. Eccles
Organizations
- Massachusetts Institute of Technology