A Practical and Robust Method to Experimentally Determine the Location of the Region of Transition from Laminar to Turbulent Flow on a Towed Body

Abstract

When performing model-scale resistance tests on bodies towed in water it is normal practice to deliberately stimulate turbulence close to the leading edge to permit appropriate scaling of resistance measurements. Alternatively, tests on towed bodies can address the flow characteristics over the body in the absence of deliberately tripped turbulent flow. In the second case an appreciation of the extent of laminar and turbulent flow over the body is of particular interest. While sophisticated and expensive methods are available to experimentally detect the location of transition on bodies in fluid flow, these are still particularly challenging when applied on bodies being towed through water. In this paper a straightforward alternative experimental method to detect transition on towed bodies is provided. This transition detection method simply uses conventional experimental measurements of drag on a towed body, subject to deliberate turbulence stimulation, to deduce the extent of laminar flow. The transition detection method is theoretically outlined and an experimental flow visualisation procedure demonstrates the required effectiveness of the turbulence stimulators used. An experimental demonstration of the proposed method is provided using two alternative turbulence stimulation devices. The conclusions indicate that the proposed method provides a practical and robust method to experimentally detect transition on a towed body with reasonable accuracy.