Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 99409

99409 - Parametric Study of an Active Grid Turbulence Generator to Reproduce Real-World Tidal Flow Conditions 

Active grid turbulence generators are custom-engineered laboratory devices used to induce turbulence in a fluid flow. Over the past three decades, researchers have closely studied and reported on the success of using an active grid in a wind tunnel; however, the literature on an active grid’s application in a water tunnel is near non-existent. The current work aims to serve as a flagship study on the use of an active grid in a water tunnel setting.

Analogous to wind tunnel studies, active grids in a water tunnel are tremendously useful in mimicking conditions in actual environmental flows for which energy capturing technology can be deployed. Tidal flows at highly energetic sites are inherently turbulent and directly influence the available energy extraction, operation, and maintenance of tidal energy converters. Field studies and demonstration projects in these environments are often cost, risk, time, and resource-intensive. Lehigh University’s Tidal Turbulence Testing Facility (T3F) has the unique capability of reproducing tidal energy site conditions in its laboratory-scale water channel. This capability is made possible by T3F’s active grid turbulence generator; currently, the only such device made for use in water in the United States. Through a detailed parametric study, the active grid and channel inflow parameters were tested such that desired turbulence statistics could be produced in the water tunnel. Fine-tuning these operating parameters has produced flows with turbulence intensity values of ~30%, mimicking the upper bounds of what is found at highly energetic tidal sites. Features such as mean velocities, turbulence intensity values, integral length scales, and power spectra will be discussed in determining the successes and ongoing challenges of recreating turbulence flow innate to tidal currents via a laboratory twin water channel. The anisotropic behavior of turbulence is also analyzed to aid in the visualization of complex fluid flow. The Reynolds-stress anisotropy tensor is employed to obtain various properties of anisotropic turbulence which can be used in turbulence modeling and visualization. Results can be plotted on an invariant map known as the Lumley triangle. These maps feature critical points and curves which correspond to particular states of the Reynolds-stress tensor and the consequent shape of the produced turbulence. Controlling the shape of turbulence is another necessary tool in the pursuit of recreating tidal conditions in a laboratory setting.

Development and benchmarking of a laboratory tidal current twin will allow early-stage tidal energy converter (TEC) developers (TRL: 1-5) to perform design iterations and structural health monitoring in a framework of tidal site-specific turbulence. Developers can identify failure modes and perform design iterations at lower TRL (≤5) levels that would make the design more robust and provide additional confidence before open water testing (TRL>6). The turbulence inflow datasets can be used for developing synthetic turbulence protocols that can be included as representative tidal turbulence spectrum for TurbSim. This data can be used in formulating international standards, such as those related to IEC TC 114, to improve load prediction standards for tidal rotors.

The authors acknowledge funding support from NSF Partnership for Innovation - Technology Transfer (PFI-TT Program, Award # 1919184).

Presenting Author: Christopher Ruhl Lehigh University

Presenting Author Biography: Chris Ruhl is currently in the third year of his PhD program in the Department of Mechanical Engineering and Mechanics. He obtained his Bachelor of Science degree in Mechanical Engineering from Lehigh in 2016 and his Master of Engineering degree in Technical Entrepreneurship from Lehigh in 2017. Upon completion of his master's, Chris worked for a software company in New York City from 2017-2019, before transitioning to his role as a civilian mechanical engineer for the U.S. Army in 2019 at the Aberdeen Proving Grounds. Ultimately, Chris decided to return to his alma mater in Fall of 2019 to begin the pursuit of his PhD in mechanical engineering. Chris’s current studies focus on the production and characterization of turbulent flow using an active grid turbulence generator as well as turbulent flow interactions with tidal stream turbine devices. Chris was a member of the Lehigh University Football team from 2012-2016.

Authors:

Christopher Ruhl Lehigh University
Arindam Banerjee Lehigh University