Design of a Recirculating Water Tunnel for the Study of High-Reynolds Number Turbulent Boundary Layers

Abstract

This paper reports on the design and fabrication of a high-Reynolds number recirculating water tunnel, which will be used primarily for the study of turbulent boundary layers with an emphasis on drag reduction applications. The primary design specifications were (i) achieve a momentum thickness based Reynolds number above 10,000, (ii) maximize optical access, and (iii) minimize flow non-uniformity. This paper discusses the design considerations and procedures to meet each of these design criteria as well as the manufacturing of the components, installation, and design of auxiliary systems such as the pressure regulation system. There are several recirculating water tunnels at universities that can achieve comparable Reynolds numbers, but they were either built with at least double the budget of the current project or are refurbished tunnels from other laboratories (i.e. key design considerations were already fixed). Thus, the current work offers a guide for the overall design of a low-cost, high-Reynolds number water tunnel. A brief review of other recirculating high-Reynolds number water tunnels is included. Currently, installation has begun with the fabrication complete.

Design and Validation of a Recirculating, High-Reynolds Number Water Tunnel

“…The as-built test-section has a flange-to-flange total length of 1.1 m with a viewable length of 0.914 m (Fig. 2) on all sides except the top, which has a 114 mm  76 mm panel to accommodate an injection plate [17]. Edge fairings were not used and the frame designed to facilitate direct line-of-sight of the tunnel wall.…”

“…A trip of uniformly distributed 122 lm silicon carbide grit was located around the test-section inlet perimeter. When pressurized p max ¼ 276 kPa ð Þ , the acrylic walls have a maximum displacement of 115 lm [17]. The resulting local curvature has a negligible impact on the velocity profile but is nontrivial compared to l .…”

“…The honeycomb sizing used experimental turbulence reduction factors and pressure-drop coefficients for a wide range of cell length and diameters [31]. An iterative process [17,23] resulted in the selection of a 610 mm (length) by 19 mm (cell diameter) polycarbonate hexagonal honeycomb (PCFR750W24, Plascore, Zeeland, MI) followed by 152 mm (length) by 6.35 mm (diameter) stainless steel honeycomb (76 lm foil, Benecor, Wichita, KS). It is recommended that 30-40 cell diameter long settling-chambers be positioned downstream of the honeycomb to utilize viscous decay to suppress their turbulent wakes [32,33].…”

“…Thus, the current work compiles information from a wide range of facilities (see Ref. [17] for complete list), which is a guide to the overall design of a relatively low-cost water tunnel capable of achieving Reynolds numbers comparable to any nongovernment owned facility and verifies the design with characterization of the as-built tunnel performance. The completed facility (schematically shown in Fig.…”

“…4). The interested reader is directed to the previous work [17,23,24] for more detailed discussion on structural design, fabrication, and installation.…”