Design Optimizations for Turbulence Reduction of a Closed-Circuit Compressed Air Wind

Open Access
- Author:
- Fink, Jason
- Area of Honors:
- Aerospace Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Mark A Miller, Thesis Supervisor
Philip John Morris, Thesis Honors Advisor - Keywords:
- wind tunnel
fluid mechanics
aerodynamics
flow separation
boundary layer control
turbulence
CAD
pressure vessel
closed-circuit
rotary systems
mesh screens
test section
wide-angle diffuser
flow conditioning
settling chamber
return diffuser
rotational augmentation
UAVs
phase-lock imaging
airfoils
pressure drop - Abstract:
- Previous work on closed-circuit wind tunnel design have shown that using mesh screens can prevent turbulence and flow separation by inhibiting excessive boundary layer growth. There are advantages and disadvantages to using a closed return wind tunnel. It is advantageous to use one because the flow can be better controlled as this will be discussed further in the design considerations. The main disadvantage is that closed return tunnels are larger and require more materials to make fully functional. Therefore, the cost for these types of wind tunnels are higher than an open return wind tunnel. The goal for the new facility at Penn State is to achieve high pressures (500psi), and in result, high Reynold’s numbers using a pressure vessel. In this work, design optimizations were developed for the wide-angle diffuser, flow conditioning region, nozzle, test section, and the return diffuser to make the flow move more efficiently by mitigating unsteady flow and minimizing flow separation and turbulence. Several unique regions of the tunnel is its wide-angle diffuser, nozzle, and test section. The wide-angle diffuser is a short diffuser with a large area ratio and cone angle that requires its boundary layer growth to be controlled to prevent flow separation. The motivation for the wide-angle diffuser was to receive a large area ratio while keeping the length of the diffuser shorter than a typical diffuser would to save space within the facility. A typical diffuser would achieve the same area ratio with a longer length. It was decided to use one screen with a pressure loss coefficient of 2.65. The uniqueness of the nozzle was to include a point of inflection in its wall shape. Two cubic equations, one that describes the wall shape before the chosen inflection point, and one that describes the wall shape after the chosen inflection point, make up the contraction contour. Finally, the large diameter of the test section is important for the purpose of allowing large models to be tested such as aircraft models, airfoils, and wind turbines. Recommendations for future work will be made depending on the data received when eventually testing all of these design considerations.