Wind Tunnel Flow Visualization

Overview

Flow visualization techniques are essential for understanding airflow dynamics around models. Laser sheet visualization stands out as a useful and effective tool. This report explores the intricacies of laser sheet visualization, its operational principles, advantages, limitations, and applications in fields ranging from aerodynamics to medicine.

Process

In wind tunnel experiments employing laser sheet visualization, the experimental setup is crucial for obtaining accurate and reliable results. The following outlines the detailed experimental procedure and precautions necessary for conducting such experiments effectively: 

Materials Required:  

• Test Object: A model representing the object of interest, a delta wing model was used

• Fine Mist: A mist generator capable of producing a finely dispersed mist of seed material, smoke was used, which will serve as the tracer particles. 

• High-Quality Laser: A laser source emitting a monochromatic beam with sufficient power and stability for illuminating the mist effectively.  

• Wind Tunnel: A wind tunnel facility equipped with a controllable airflow system, where the experiment will be conducted.

 Experimental Setup: 

• Position the test object securely within the wind tunnel, ensuring it is properly aligned for the desired flow conditions.  

• Install the mist generator at an appropriate location upstream of the test object, ensuring uniform dispersion of the mist throughout the airflow.  

• Align the laser source to illuminate the mist sheet generated by the mist generator, ensuring that the laser sheet intersects the region of interest around the test object.  

• Adjust the intensity and focus of the laser beam to achieve optimal illumination of the mist sheet, maximizing visibility of the flow patterns. 

Observations

The motion of gases is invisible to the observer during direct observation of the experiment; however, the use of laser techniques allows the observer to understand flow visualization. This visualization can also be captured with the use of digital cameras such as an iPhone. Throughout the experiment, our group used our iPhones to capture flow visualization in the wind tunnel, as depicted in many of the figures in this report. The wind tunnel allows angle of attack adjustment of the object being tested. An observer can easily identify changes in gas flow resulting from the new angle of attack. This flow change can be used to identify vortices, flow disruptions, common flow patterns, and much more. During the experiment, our group identified different scenarios of flow disruption over the airfoil that led to a loss of lift, also known as a stall. The presence of an observer serves as an important check and balance in airfoil testing because it allows a simple eye test of flow over an airfoil. One should never rely solely on a flow visualization test to approve the commercial use of an airfoil; however, it is a simple tool that can immediately identify basic patterns and behaviors of gas flow over an airfoil.

References 

1. NASA Glenn Research Center. "Tunnel of Air." NASA Glenn Research Center, n.d., https://www.grc.nasa.gov/www/k-12/airplane/tunvlaser.html. Accessed April 8, 2024 

2. Dr. Taghavi’s AE 445 Flow Visualization Slides. Accessed April 9, 2024 

Gallery