Accessing quantitative heat transfer with Temperature Decline Thermography

Abstract

Analyzing local heat transfer on complex components in fluid flows is crucial for the optimization of modern aerodynamical systems. Many flow situations like in gas turbines, are difficult to access and require fast measurement techniques which offer two-dimensional information with negligible impact on flow conditions. Therefore, a transient measurement technique based on infrared thermography is investigated to access local heat transfer coefficients without contact by means of a calibration. A flat plate in a free-jet is used as a calibration vehicle where results are compared to the flat plate Nusselt correlation in laminar flow. To transfer the observed linear calibration relation to different flow conditions, a turbulent boundary layer is generated and results are compared to the turbulent Nusselt correlation. Good agreement of converted measurement data and theory is obtained. Temperature Decline Thermography (TDT) was introduced by the authors to qualitatively measure laminar-turbulent transition. In this work TDT is extended to access quantitative heat transfer coefficients.