Welcome! I'm Rui Ni, an Assistant Professor of Mechanical Engineering at Penn State. I'm directing the Fluid Transport Lab. Our research interests broadly revolve around experimental studies of turbulence, multiphase flow, heat transfer, physiological flow, and swarming insects. A persistent theme throughout most of these areas is the challenge to model and predict the complex behaviors of coexistent phases, the phenomena that they manifest in multiple time and length scales, and the emerging dynamics due to intra- and inter- phase couplings. To navigate in this research domain, the other part of our work is devoted to advancing experimental tools, including the non-invasive Lagrangian particle tracking system, visual-hull reconstruction, and the minimum-invasive method, such as miniaturized sensors.
We are working on improving the existing 3D particle tracking code to handle high tracer concentrations (up to 0.1 particle per pixel). The aim of this project is to demystify the high-concentration tracking algorithm in 3D and make it more transparent for students and non-experts to use. The other great feature of this new in-house code is the simple parallelization for computer clusters and quantification of propagation of experimental uncertainty. This will help us to better understand, evaluate, and eventually control the measurement uncertainties.
The V-ONSET facility provides a unique flow environment for us to probe the interfacial couplings between two phases in the Lagrangian framework. That includes bubble deformation and breakup physics, as well as simultaneous measurement of the surrounding turbulent flow.
Multiphase flow can often find its applications in boiling heat transfer and chemical and biological reactors. A common feature of these applications is the mass and heat exchange between two phases via complex interfaces. The aim of this project is to unveil the underlying physical processes and bridge the scale difference between the microscopic interfacial dynamics to macroscopic transport and mixing statistics.
A perfect geometrical reconstruction of a sophisticated 3D object requires infinite optical views covering all possible angles around the object. This is not always feasible or affordable for high-speed imaging, as the fast cameras are expensive. With the reduced number of cameras, the traditional Visual Hull method suffers from a problem that some virtual mass appears in the reconstructed volume, contributing to relatively large uncertainties. We have designed a novel virtual camera method to mitigate this problem. This framework is designed mostly for our bubbly flow application, but it can also be used for other applications. Please send Dr. Rui Ni an email if you want to collaborate on this idea.
In addition to bubbly flows, another large category of multiphase flows is the flow of gas-solid mixture. There are many applications in this area, including dust brownout by helicopters, dust ingestion into engines, and dust trail trailing ground vehicles. In FTL, we have repurposed a low-speed wind tunnel for a new dust tunnel. This tunnel provides a controlled environment to study problems, such as dust trail for ground vehicles and dusty aerodynamics for austere environments.
Multiphase flow is also ubiquitous in subsurface oil reservoir, where the environment is rather porous. If a porous medium flow is contaminated with fine particles, those particles can gradually deposit on the surface of grains, reducing the permeability of the reservoir and thus lowering the production efficiency of oil. Supported by the American Chemical Society PRF grant, we aim to provide new insights in this problem by visualizing the entire process in a refractive-index-matched porous flow system.