Turbulent and Multiphase Flows
Preferential
concentration of particles (solid particles or droplets) by turbulence, the
spatial characteristics, and dynamics of clusters of particles, and their
impact on the carrier fluid, are of upmost importance to a vast array of
applications. Industrial and energy processes, pollution dispersion and risk
mitigation, vehicle aerodynamics and system damage in dusty flow operations, are
few of them.
Our group has built the US longest vertical channel flow facility to study turbulent-particle laden flows. With a total channel length of 225 times its width, fully developed turbulence is ensured at the 2m long acrylic test section. It can operate at Reynolds numbers based on channel width up to 82000 (friction Reynolds number about 2000). Its modular design enables a wide range fundamental research on wall-bounded turbulence and particle-laden flows such as the impact of surface roughness, heat transfer or electrostatic effects.
Ongoing efforts: Clustering temporal statistics, formation and desintegration of particle clusters by turbulence; Adjoint-based Training of Embedded Neural-Network Models for Particle-laden Turbulence
Graduate researchers: German Saltar Rivera, Abel Viji George
Postdoc: Tuhin Bandopadhyay,
Collaborators: Jonathan Freund
PLUME SURFACE INTERACTIONS
What happens when a rocket operates near a surface ?
During the final descent of a powered space exploration vehicle onto the landing site, the high-speed plume interacting with the surface can significantly alter the local topography and create dense clouds and sheets of eroded material. Mission risks associated to plume-surface interactions (PSI) vary widely with thruster, atmosphere, and surface properties, all playing critical roles on surface erosion, crater formation, regolith entrainment and ejecta dynamics. Advancing our understanding of plume surface interactions and developing models that capture the leading physics are essential for future space exploration missions,
Our group at UIUC uses two sub-scale, inert-gas, PSI facilities and diverse measurement techniques to understand the complex interplay between flow, particles and granular media dynamics. Experiments in vacuum are used to reproduce flow physics relevant to planetary and Lunar landings using jets up to Mach 5. Tests at ambient pressure expand the envelop of non-dimensional numbers and are directly relevant to vertical take-off and landing on Earth. Non-intrusive characterization of flow, ejecta dynamics and cratering is achieved by combining multiple diagnostics such as high-speed Schlieren, Nitric Oxide Planar Laser Induced Fluorescence, surface pressure sensors, planar particle-tracking velocimetry, high-speed imaging with volumetric illumination, 3D photogrammetry, and millimeter wave interferometry. Our work is advancing the state of the art knowledge on PSI and the development of semi-empirical models with predictive capabilities. Our dataset are open to the community for validation of computational tools.
In collaborations with researchers at University of Michigan, we are developing data driven engineering models for crater formation and erosion to support future mission design and risk mitigation strategies. We leverage half-space crater evolution data from NASA Physics-Focused Ground Test (PFGT) campaign, carried out at Marshall Space Flight Center during 2021 and 2022, in addition to that from our 3D experiments.
Graduate researchers, current: Callahan Eshleman, Liam Heuser, Lorenzo Bruni, Claudia Jimenez Cuesta.
Collaborators: Joshua Rovey, Fabien Evrard, Jesse Capecelatro
Underexpanded jet impingment phenomenology
Summary of diagnostics and representative data outputs
Measurements in optically opaque particle clouds
Seeing through dense clouds with mm-waves
How can we measure the amount of suspended material in a dust storm, the water content in very dense clouds, or the ejecta concentration lifted by a rocket impinging on the ground? When light attenuation in the visible part of the spectrum is too large, and scattering of light by particles is also unfeasible, we still can make quantitative measurements.
The secret is to vary the wavelength, move away from the optical regime. As the wavelength increases the extinction produced by a particle decreases rapidly. By using COTS radars, conventionally used in the automotive industry as distance sensors, but exploiting in a different way, our group at UIUC has developed a new instrument capable of measuring volume fraction of suspended material. The new instrument is light, compact, affordable, and paves the way for flight instruments that can be used in harsh environments.
Graduate researchers: Liam Heuser, Nicolas Rasmont (graduated)
Collaborators: Joshua Rovey
Phase shift measurement concept
FMCW Radar interferometry concept
Tomography
Time-resolved radial distribution of particle concentration
Supersonic particle-laden flows
Momentum exchange between particles and fluid can significantly alter the otherwise single phase flow. Precipitation, clouds, atmospheric debris, or water mist at low altitude, all behave as inertial particles when interacting with a high speed vehicle. Non only they can damage the vehicle under impact, they also affect the flow field around the vehicle. Experiments are performed in our group using an underexpanded Mach 1 jet loaded with glass beds of 117 um nominal diameter in a setup that allows independent control of the particle feeding rate and the particle discharge velocity and position within the jet settling chamber, as well as the air mass flow. Well controlled experiments are key to validate drag models for high loading compressible flows. Due to the particle inertia, particle and flow acceleration within the nozzle need to be quantify for apples-to-apples comparisons of flow modifications and particle statistics in different experiments (numerical or experimental.
Schlieren flow visualization, Mach 1 underexpanded jet with increasing particle loading
Mach disk position variation with particle loading and jet expansion
Magnetic Resonance Imaging for fluid dynamics.
Three-dimensional flows, and particularly in complex internal flow configurations or along complex topographies, pose major challenges to designers, to numerical predictions, and to conventional experimental approaches. What can we do to study these flows of much practical interest where high-fidelity simulations are unaffordable, low fidelity ones not sufficient for design optimization, and, due to limited optical access, intrusive point-wise measurements are often times the only option? The answer is Magnetic Resonance Imaging (MRI). MRI is extensively used in the medical field, but its potential extends to many disciplines, including fluid dynamics.
Our
group is working with researchers at the Biomedical Imaging Group (BIC)
at Beckman Institute to advance MRI based techniques for
three-dimensional velocimetry and concentration measurements, MRV and
MRC, respectively. Our test sections consist on SLA models that
reproduce the flow configuration under study and instead of a wind
tunnel we use water flow loops that ensure a constant and uniform flow
velocity at the inlet. Prototype to 3D results times are reduced
compared to the use of conventional wind tunnel testing, and
non-dimensional aerodynamic parameters are equally matched.
What for? Anything and everything where laser-based diagnostics cannot provide data because of a wall, because of complex geometry, etc. Ideal for design optimization as we can measure 3D flow fields much faster than in classical wind tunnels from concept to data. Data collected on different designs can be used to build a wide dataset for ML approaches.
Postdoc:: Tuhin Bandopadhyay,
Collaborators: Andrew Banko (West Point, USMA), Brad Sutton.
MRI setup
Flow over an inhomogeneous roughness array with jet in cross flow. Test section (top left), 3D velocity field (bottom), in-plane velocity showing jet updrift (top right)
3D velocity flow field around a generic stadium for varying wind angles, ventilation dynamics
Parachute fluid and structural mechanics
Fluid Structure interactions in flexible and porous materials
Graduate researchers: Cutler Phillippe,
Collaborators: Francesco Panerai, David Ehrhardt
