Optical Gas Flow Diagnostics

01 | Problem Statement | Invisible Boundary Challenges

• Problem: Critical fluid boudnaries, gas flows, and mixing layers are inherently invisible to standard camera sensors.

• Challenge: Physical sensors block, drag, and deform the fluid dynamics they attempt to measure.

• Engineering Goal: Construct a non-invasive, high-speed optical system to visualize gas density gradients from a concentric CO2/nitrogen flow tube.

02 | Analysis & Design Process | Optical Physics & Mechanics

• Density-Drive Refraction: Local density changes caused by flow of CO2 and nitrogen alter the gas's refractive index, bending the laser beam at different angles.

• Optical Path: A laser beam is routed through mirrors, lenses, and an iris, then focused onto a knife-edge and imaged with a camera.

• Schlieren Technique: Knife-edge blocks part of the beam, converting first-order refraction angles into bright & dark contrast.

• Shadowgraph Technique: Removing the knife-edge projects deflected beams directly onto the sensor, mapping second-order density fluctuations.

03 | Manufacturing & Testing | Testing & Flow Visualization

• Schlieren results: Clearly imaged turbulence and uneven flow at the gas outlet, exposing invisible flow characteristics.

• Shadowgraph Comparison: Same flow appeared smoother with less fine-scale detail, confirming Schlieren's higher sensitivity to small fluctuations.

• Alignment Control: Achieved a usable image by isolating ambient light, correcting imperfections in the laser beam, and keeping dust off the image filter.

Luke Stratakos | lstratak@stanford.edu | linkedin.com/in/luke-stratakos/