Novel Environment Enables PIV Measurements of Turbulent Flow around and within Complex Topographies

A novel flow facility developed to enable a broad spectrum of fluid mechanics experiments involving complex geometries and employing high-fidelity optical diagnostics is described in this paper. The development of the facility, which comprises two fully operational refractive-index-matched (RIM) flow tunnels, was guided by the ambition to overcome experimental roadblocks that often inhibit the experimental study of high Reynolds-number geophysical and environmental flows with modern techniques, like particle image velocimetry. The methodology described in this paper leverages and integrates new technology, including rapid prototyping methods to fabricate geometrically complex flow models and advanced optical methods for probing the physics of fluid flows. The aim of this paper is to provide a full technical description of the facility, to introduce the experimental protocol, and to quantify measurement uncertainties associated with imperfect index match. This protocol has been applied in a number of recent and ongoing research projects wherein measurements that would be impossible in a standard wind or water tunnel due to limited optical access have been successfully enabled, demonstrating a new spectrum of capabilities. Examples of results obtained for three different geophysical applications are presented in this paper to highlight the technical challenges that have been tackled and to discuss suitability for potential new applications.