Design of a High Speed Water Tunnel Force Balance & Testing of High Performance Hydrofoils for Marine Hydrokinetic Turbines
This report reviews the force balance that was designed and manufactured for the UNH Six-Inch High-Speed Water Tunnel. This report also examines the design and testing of a high performance bi-directional hydrofoil for marine hydrokinetic turbines and design of a sting with cavitation assisting capabilities for studies of super-cavitation.
The force balance can read in both lift and drag measurements simultaneously, separately, and accurately. The force balance was designed for operating conditions of an up to 12 m/s (26.84 mph) flow velocity in the test section and variance in the absolute pressure from 0.2 to 2 bar (2.9 to 29 psi). The force balance is currently equipped with force measuring devices designed to test lift loads of up to 960.8 N (216 lbf) and drag loads of up to 22.2 N (5 lbs). Calibration results revealed a lift force sensitivity of 2.32 µε/N (10.30 µε/lb) and a drag force sensitivity of 2.66 µε/N (11.85 µε/lb).
The force balance allows for the testing of hydrofoils used in marine hydrokinetic turbines which currently require pitch control for bi-directional flows. A bi-directional hydrofoil will possibly decrease the cost of hydrokinetic turbine production through negating the requirement of pitch control which increases the base cost of turbines and following maintenances. The hydrofoil was designed through the modification of the NACA 63-424 hydrofoils section. Calculations using JavaFoil revealed that at their maximum efficiencies, the original NACA 63-424 hydrofoil outperforms the experimental bi-directional hydrofoil with lift to drag ratios of 67.48 to 54.32 respectively. In certain scenarios the penalty of decreased performance can be outweighed by the decrease in overall turbine cost and maintenance.
A sting was designed to study the effects of super cavitation in relation to drag reduction. The sting has assisted cavitation capabilities with two ports for ventilation and pressure measurements. It utilizes a reversible mounting system to enable upstream and downstream cavitation testing. The sting can test multiple heads using an interchangeable cap system. More data will be collected as testing continues on the sting and the high performance hydrofoils.
Measuring the characteristics of 2-D hydrofoils is critical to better understand how to efficiently use them for marine hydrokinetic applications. Through the use of this force balance the UNH High Speed Six Inch Water Tunnel will help the UNH Center for Ocean Renewable Energy expand its capabilities in performing essential research.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Design of a high speed water tunnel force balance & testing of high performance hydrofoils for marine hydrokinetic turbines (2012). Ryan Therrien, Spencer Roux and Ben Comtois. Advisor: Martin Wosnik.