Confessions of a Hot-Wire User: High-Resolution or High-Illusion in Wall-Bounded Turbulence?
Ramis Örlü
Abstract: For nearly a century, and still today, hot-wire anemometry has shaped how we see turbulence, particularly in wall-bounded flows. Its reputation for unrivaled temporal and spatial resolution made it the trusted companion of generations of turbulence researchers–including myself. Yet this status also masks important limitations. Hot-wire anemometry remains central to studies of near-wall turbulence and has fueled several long-standing as well as more recent debates. These debates concern not only the magnitudes of turbulence quantities but even their qualitative trends, and the differences between proposed scaling laws often fall within the uncertainties of the measurements themselves. Over the years, a range of best practices and corrections for spatial and temporal resolution, near-wall interference, blockage, and other effects have become so routine, so adapted, and so accepted that they are no longer explicitly mentioned. In retrospect, we may have been too confident, and some of these practices and corrections may no longer be appropriate in the context of today’s quests. As someone who has spent much of a career working with hot-wire data, I find myself asking: have I always been studying turbulence itself, or sometimes the limitations of the probe I relied on? While laser-optical techniques have pushed the boundaries of spatial and temporal resolution, hot-wire anemometry continues to occupy a peculiar position: widely used, yet inherently constrained.
This keynote revisits both the legacy and the continuing role of hot-wire anemometry in wall-bounded turbulence research, asking whether it still provides our sharpest lens on turbulence or whether it has become an illusion of resolution we hesitate to give up.
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