The video depicts a fog machine producing fog in a secluded area with a vent.

Team First – Fog Flow

Cooper Wyrick

Team First

MCEN 4151-001

September 16th, 2025

Teammates: Zach Taylor, Kai Hansen

This project was part of the “Team First” assignment in Flow Visualization, where our group aimed to capture and reveal fluid flow phenomena through a collaborative setup. We chose to work with a fog machine in a dark, ventilated room to visualize turbulent and laminar air motion. The intent of our image and video was to capture the upward dispersal of fog illuminated by a single light source. We wanted to highlight the chaotic vortices and the overall dissipation pattern as the fog interacted with airflow from a ventilation system. Our process included multiple test runs with adjusted camera and lighting angles before producing the final shot. One team member operated the fog machine, another assisted with camera positioning, and I managed lighting.

The flow apparatus consisted of a ground fogger by Intertek using Fogger Endcap 240 11 6314 solution. The fog was released into a dark room with a ventilation system pulling the air upward and away. A light from an iPhone SE was placed below the fog stream to highlight its motion. The Samsung Galaxy S25 camera was positioned perpendicular to the light beam, to record in slow motion. The fog was initially released at an approximate velocity of 2 m/s based on visual inspection, then slowed to 0.5 m/s as it dispersed under the influence of the ventilation system 2 meters above. The schematic diagram below shows the setup.

Figure 1: Schematic of Setup

From a fluid mechanics perspective, this is a turbulent jet interacting with forced convection from a ventilation system. The fog exhibited chaotic mixing typical of turbulent flow. A Reynolds number estimate can be made assuming U = 2 m/s at the exit of the fog machine. The diameter of the slot where fog left the fog machine was approximately .05 meters (2 inches). The flow rate at the exit of the fog machine can be calculated from these values as Q = UA = 2(m/s) * π(.025)2(m2) = 0.003926 m3/s. The kinematic viscosity of stage fog can be approximated as the same as air at room temperature at sea level and 1 atm. This value is v = 1.460 × 10⁻⁵ m²/s (“Resources” 2025).

Re = UD/v = (2 (m/s) *.05 (m))/1.460 x 10-5(m2/s) = 6,849.315

Equation 1: Reynold’s Number of the Flow

This Reynold’s number indicates turbulent flow upon exiting the fog machine. As the fog speed approaches 0.5 m/s, a laminar flow is established as the Reynold’s number becomes 1,712.3.  Forces acting include buoyancy due to the temperature difference, inertia of the fog jet, and entrainment from the ventilation airflow.

In The Fluid Mechanics of Natural Ventilation (P.F. Linden, 1999), Linden explains that pressure differences caused by buoyancy and wind drive exchange flows through vents. This means that the stage fog, being suspended droplets in air, is carried along with the entrained airflow and pulled into the vent by the same pressure-driven mechanism.

The visualization technique relied on fog as a seeding material for airflow. The fog solution Fogger Endcap 240 11 6314 was used, providing visible vapor. The dark room environment created high contrast between illuminated fog and background. Lighting was provided by an iPhone SE flashlight, aimed upward from below the fog stream. This backlighting emphasized the motion of the fog by scattering light through fog particles. The room’s ventilation provided additional motion and dispersion.

The final visualization was captured using a Samsung Galaxy S25 in slow-motion video mode, positioned about 8 inches from the fog. The light source (iPhone SE flashlight) was 2 inches below the fog. The focal length was a 24mm equivalent. The aperture was F 1.7. The shutter speed was ⅛. The ISO setting was 3200 (DXOMARK 2025). The video field of view spanned approximately 533×300 mm across the fog plume. Slow-motion was enabled at 240 frames per second to better reveal turbulent spirals. Post-processing was completed using the Colourtone app, where contrast and temperature were increased to sharpen the visual appearance of the fog and highlight its warm glow under the lighting. The video was also cropped to focus on the transition between turbulent to laminar flow. The original video’s dimensions were 1280 x 720 pixels. The edited video was 916 x 516 pixels.

The video reveals chaotic mixing as fog interacts with ventilation currents. I like how the lighting highlights edges on the rising fog, emphasizing vortices and flow structures. The slow-motion recording made otherwise imperceptible eddies more visible, helping us better appreciate the turbulent physics. A limitation of the video is that exposure settings were not controlled, and some areas appear over-bright, losing detail. Additionally, the field of view was narrow, so we did not capture the larger-scale dispersion. In future work, I would like to try using a laser sheet or stronger directed lighting to better highlight velocity gradients and possibly apply particle image velocimetry (PIV) techniques. Overall, the intent of revealing turbulent fog motion and interaction with surrounding ventilation was fulfilled, and the project helped me better appreciate how lighting and framing affect fluid visualization.

Appendix

DXOMARK. “Samsung Galaxy S25 Ultra Camera Test – Retested.” DXOMARK, 25 June 2025, www.dxomark.com/samsung-galaxy-s25-ultra-camera-test-retested/. Accessed 1 Oct. 2025.

Linden, P. F. “The Fluid Mechanics of Natural Ventilation.” THE FLUID MECHANICS OF NATURAL VENTILATION, maeresearch.ucsd.edu/linden/pdf_files/75l99.pdf. Accessed 1 Oct. 2025. 

“Resources | Aerodynamics for Students.” Aerodynamics4students.com, 2025, www.aerodynamics4students.com/properties-of-the-atmosphere Accessed 1 Oct. 2025.