On the relevance of time-resolved temperature maps in bounded flow investigations

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Kurzfassung

A strong interdependence exists between the thermal and momentum boundary layers. This relationship—historically referred to as the Reynolds analogy—establishes a connection between heat transfer and fluid friction in bounded flows, asserting that the same flow-induced structures govern both processes. As a direct consequence, the behavior of the flow over a slightly heated surface can be inferred from the evolution of the wall temperature field, Tw(x, y, t), where local temperature gradients are typically correlated with the distribution of wall shear stress. However, this assumption may induce misleading results in the experimental analysis of boundary layers about, e.g., the detection of flow separation and reattachment, which do not necessarily occur at the minima and maxima of the time-averaged wall temperature: in fact, this kind of distribution can also originate as the consequence of other flow dynamical phenomena, such as laminar-turbulent transition. Such effects complicate the interpretation of thermal measurements and may lead to misinterpretations or spurious correlations. This risk of misinterpretation can be avoided by using an alternative approach, which considers a complementary description of the surface flow in terms of the celerity of displacement of thermal perturbations of T ′(x, y, t) = Tw(x, y, t)−T w(x, y) (blobs) under the influence of τw. This representation does not rely, at least to a first-order approximation, on spatial temperature gradients ∂T/∂xi. Recent advances in Temperature-Sensitive Paint (TSP) applications have greatly enhanced this technology, enabling non-intrusive measurements of the surface temperature distribution Tw with high-resolution in both space and time. This technique offers an innovative and visually compelling means of investigating near-wall fluid dynamical processes, allowing instantaneous observation of complex flow phenomena and their evolution.

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• On the relevance of time-resolved temperature maps in bounded flow investigations. (deposited 05 Aug 2026 14:53) [Gegenwärtig angezeigt]