Session: Student Poster Competition

Submission Number: 187095

Rapid Prototyping of a Constant-Velocity Acrylic Test Section for High-Subsonic Wet Wind Tunnels 

The formation and shedding of Coarse Water Droplets (CWD) from the trailing edges of Low-Pressure (LP) steam turbine blades is a primary cause of blade erosion and thermodynamic efficiency loss in power generation systems. To investigate the fundamental physics of this film-shedding process, Professor Vincent McDonell’s UC Irvine Combustion Laboratory utilizes a specialized high-speed experimental facility in support of ongoing research sponsored by Mitsubishi Heavy Industries. This poster details the rapid design, fabrication methodology, and aerodynamic validation of a cost-effective, constant-velocity acrylic test section engineered to support high-subsonic flow testing while maintaining critical optical access for non-intrusive diagnostics.

The experimental study employs a 100mm chord NACA 0012 airfoil. In conventional straight-duct test sections, the physical blockage of the airfoil accelerates the flow, skewing aerodynamic data. To counteract this and simulate a more uniform turbine passage flow, a modified acrylic test section was designed where the side walls converge inward at a 3.8-degree angle. This convergence joint was strategically aligned with the maximum thickness point of the airfoil. Pre-test Computational Fluid Dynamics (CFD) analysis, utilizing an SST k-ω turbulence model, predicted that this geometric modification would successfully shift the flow field, resulting in a velocity profile approximately 10% closer to a constant velocity from the leading edge to the trailing edge compared to a standard straight duct.

To realize this design under strict timeline and budget constraints, the project utilized rapid design/build/test principles. The test section was entirely self-manufactured in-house using laser-cut acrylic plates, manually machined via drill press, and structurally secured using self-tapping screws. This methodology yielded a highly sturdy, leak-free apparatus with pristine optical clarity.

Empirical aerodynamic testing was successfully conducted at a baseline velocity of 40 m/s. The physically gathered data closely matched the predictive CFD calculations, successfully validating the constant-velocity design intent. Furthermore, the acrylic structure demonstrated excellent mechanical integrity, with no damage or fatigue observed during operation. While the ultimate goal of the test section is to simulate aggressive turbine passage flows approaching Mach 0.6 (175 m/s), unexpected facility infrastructure limitations (compressor maintenance) restricted this initial physical validation phase to the 40 m/s baseline. Future work will utilize this validated test section to push into the Mach 0.6 regime to further investigate high-frequency turbulent behaviors and high-speed two-phase atomization.

Presenting Author: Caleb Commisso University of California, Irvine

Presenting Author Biography: Caleb Commisso is a second-year undergraduate research assistant at the UC Irvine Combustion Laboratory, specializing in propulsion test hardware fabrication and high-speed flow diagnostics. In support of the Mitsubishi Heavy Industries (MHI) sponsored research group under Prof. Vincent McDonell, Caleb engineers and rapidly fabricates optically accessible, constant-velocity wind tunnel test sections. His work focuses on bridging the gap between theoretical CFD models and experimental reality, utilizing precision machining and strict GD&T to ensure structural integrity under high-dynamic-pressure loads (up to 175 m/s). In addition to hardware fabrication, Caleb is currently working on stereoscopic high-speed visualization and data analysis of two-phase liquid film breakup regimes.

He is a UCI UROP Fellow and will study at Cambridge University this summer.

Authors:

Caleb Commisso University of California, Irvine
Brandon Esquivas UC Irvine Combustion Lab
Soichiro Tabata Mitsubishi Heavy Industries, LTD.
Shigeki Senoo Mitsubishi Heavy Industries, LTD.
Vincent McDonell UC Irvine Combustion Laboratory