The Development of a New High Aspect-Ratio Turbulent Channel Flow Facility

Abstract: Turbulent channel flows are of great interest for investigations of modified wall boundary conditions due to their well-understood characteristics and their broad applicability. In a reversal of typical trends, they can often be more difficult to investigate experimentally than to simulate owing to the far-reaching influence of corner effects as well as the need for development lengths in excess of 200 channel half-heights in order to produce high-quality flow. In order to rovice experimental results to compare directly with current and future computational studies conducted in the FSG group, a new experimental channel flow facility has been designed for use with state-of-the-art optical measurement techniques such as planar and stereoscopic µPIV. To further aid in understanding the flows in and around complex surfaces, a water-NaI solution will be used as the working fluid for refractive-index matched experiments. A holistic design approach has been taken, taking into consideration design, manufacturing, operational, and experimental requirements and limitations. The facility has been designed with modularity as a key focus and the channel is subdivided into three interchangeable sections with the capability to support a wide range of experimental set-ups and configurations with minimal modification. To produce a high-quality flow, the channel has an aspect ratio of 20 : 1 and a development length of 288δ preceding the test section. Based on inital design estimates of pressure losses in the system, a 11 kW centrifugal pump has been specified and is projected to allow the channel to reach its maximum design flow velocity of 10 m s¯¹. Reτ of 2300 can be achieved, allowing for investigations well into the turbulent regime which remain within the range of Reynolds numbers that can be resolved in DNS studies.