Event-triggered background-oriented schlieren: high-frequency visualization of a heated jet flow

Area of Science:

• Fluid dynamics
• Optical diagnostics
• Flow visualization

Background:

• Traditional high-frame-rate background-oriented schlieren (BOS) techniques suffer from short operating times.
• There is a need for continuous, cost-effective flow visualization methods capable of high frame rates.

Purpose of the Study:

• To introduce and validate a novel event-triggered background-oriented schlieren (EBOS) technique.
• To demonstrate the capability of EBOS for continuous, high-frame-rate flow measurement.
• To assess the accuracy and applicability of EBOS in characterizing flow dynamics.

Main Methods:

• Development of an event-triggered BOS system combining an event-triggered camera and pulsed laser speckle projection.
• Reconstruction of BOS images using event data from pulsed laser speckle projection.
• Processing of BOS images to determine flow density and temperature distributions.

Main Results:

• The EBOS technique enables continuous visualization and recording of flows at kiloframes per second (kFPS) frame rates.
• Temperature measurements of a hot air gun showed agreement with thermocouple data within a 10.8% error margin.
• The technique successfully captured the evolution of jet temperature for over 150 seconds and visualized unsteady turbulent structures.

Conclusions:

• The developed EBOS technique provides a cost-effective solution for continuous, high-frame-rate flow visualization.
• EBOS accurately measures temperature distributions and dynamic flow structures, overcoming limitations of existing BOS methods.
• This technique opens new possibilities for studying transient and turbulent phenomena in fluid flows.