Advanced laser flow diagnostics provides valuable experimental data of complex flows. Such complex flows, including turbulent flows, multiphase flows and
flows in biological systems, are ubiquitously found in nature and industries. For better understanding, modeling and control of such flows, detailed full-field measurement is needed, which is now possible
through cutting-edge techniques such as Holographic Particle Image Velocimetry (HPIV), Stereoscopic PIV, Laser Induced Fluorescence, and multi-component Laser Doppler Velocimetry. The Laser Flow Diagnostics
Laboratory (LFD) is a multidisciplinary research laboratory that leads the development of HPIV and the application of these techniques to complex flow. The LFD research team is continually searching beyond
the limitations of existing knowledge, challenging the frontiers of turbulence and complex flow research by combining state-of-the-art optical diagnostics techniques with physics, theory, experiments, and
latest computation/visualization tools.
Development of High Resolution Holographic Particle Image Velocimetry
The latest advancement of flow diagnostics technology has brought about new opportunities to provide heretofore-unavailable detailed experimental data in turbulent flows. This is the result of a breakthrough in full-field quantitative visualization – holographic particle image
velocimetry (holographic PIV or HPIV). HPIV measures turbulent flow velocity fields instantaneously in three-dimensional (3D) space with spatial resolutions comparable to those of direct numerical
simulations (DNS). To explore the maximum performance capabilities of HPIV including spatial resolution, we develop a fully automated HPIV system based on off-axis holography, distributed
computing, and 3D data processing software. Fundamental issues regarding holographic particle imaging, including intrinsic aberration, speckle noise, and dynamic ranges are studied. The system has been
applied to a number of turbulent flows. Further research on HPIV will address more reliable and intelligent processing, extension of measurement capabilities including accuracy, resolution and dynamic
range, and extension to holographic movie. Application of this unique, cutting-edge measurement tool to address critical fluid dynamics questions is under way.
Development of Digital HPIV
In making holography an easy-to-use technique, digital holography is very promising. It records holograms directly to digital
media such as CCD sensors and reconstructs the holograms numerically. Practical implementation of digital holography was not feasible until recently when the technologies of digital recording devices
and computers have been advanced significantly. In LFD lab, we are developing a digital holographic PIV system for flow diagnostics. Since digital recording of holograms eliminates the need of wet chemical
processing, we can implement cinematic HPIV and real-time measurement. Such a technique has great potential in microfluidics, multiphase flow, and biomedical flow applications.
Particle-Turbulence Interaction
The aim of this research is to advance the state of knowledge on particle-turbulence interaction in dilute, disperse, two-phase
flow. This is achieved by using cutting-edge holographic PIV techniques to provide detailed, coupled, three-dimensional (3D) data of the particulate and fluid phases, comparing the data with computational
models, and developing new understanding of the fundamental physics. Particle-laden turbulent flows are important in numerous industrial processes such as particle synthesis, spray combustion, and
sedimentation transport, and in nature. In the atmosphere, cloud droplet formation and growth is strongly affected by the droplet interaction with fine-scale turbulence. The latest advancement of flow
diagnostics technology has brought about new opportunities to provide heretofore-unavailable detailed experimental data in dilute particle-laden two-phase turbulent flows. This research is supported NASA
Microgravity Fluid Physics Program.
Mixing and Vortex Dynamics
Fundamental understanding of mixing and vortex dynamics is essential to the improvement of many industrial mixing processes. The food, chemical
and pharmaceutical industries depend on efficient mixing technologies to manufacture many of the products we use every day. Through the interrogation of the flow fields using advanced laser flow
diagnostic techniques including HPIV and laser induced florescence and numerical simulation we are able to greatly improve our understanding of such processes and the flow physics. Problems studied at LFD
lab include vortex dynamics in flow past a surface-mounted tab, and mixing characteristics of jet in a confined cross flow.
COMBUSTION
The complexity of combustion systems often limits our ability to handle such phenomena without the help of computers. The research in combustion primarily focuses on
large-scale numerical simulations and modeling of a variety of chemically reacting flows.
Diffusion Flame-Vortex Ring Interaction: A Numerical Study (Madnia)
A laminar vortex ring is generated by a jet of fuel-inert species mixture that enters a quiescent medium
of the same composition and temperature. The fully formed vortex ring interacts with a quasi-steady diffusion flame
that is perpendicular to the ring's axis. Direct numerical simulation is used to solve the compressible
Navier-Stokes equations coupled with the energy and the species equations. The Arrhenius-type reaction between the two
chemical species is taken to be second order and irreversible. Both finite rate and infinitely fast chemical
reactions are considered.
Large Eddy Simulation of Two-Phase Metalized Combustion Systems (DesJardin)
This effort is to examine the ignition and combustion of fine aluminum particles dispersed in a carrier gas
containing multiple oxidizing agents. The focus of the research is to develop models for ignition and burning processes of aluminum particles.
These particles are often employed for use in the design of explosives and are also used as an additive in propellants to enhance specific
thrust. The goal of this effort is use the aluminum particle models to simulate and understand the flow dynamics of highly energetic shock
induced dispersal events.
Modeling and DNS of Hydrocarbon Flame-Vortex Interactions (Madnia)
The main objective of this study is to gain a fundamental understanding of the physicochemical processes
that occur during the combustion of non-premixed laminar hydrocarbon fuels. The main thrust of this research is to
conduct direct numerical simulations (DNS) of non-premixed flame-vortex interactions with inclusion of
"realistic" chemistry models. The DNS-generated results will then be used to develop kinetic mechanisms for unsteady
combustion systems.
Numerical Simulation and Modeling of Fire Suppression (DesJardin)
The objective of this research is to develop an advanced modeling and simulation framework for predicting the
suppression of large scale fires using water mists and sprays. The modeling is based on Large Eddy Simulation (LES) techniques using
probabilistic based subgrid scale (SGS) models to account for multiphase coupling of buoyantly driven turbulence, combustion, suppression
thermo-chemistry, droplet transport and thermal radiation heat transfer. The main challenge in controlling large fires is predicting the
performance of the delivery system that depends on the understanding of dynamics of flame suppression processes in highly turbulent, strongly
radiating, multiphase, combusting flows. One of the goals of this research is to provide a high fidelity predicative tool to simulate these
processes. Such a tool will allow fire protection engineers to design better fire suppression systems to insure fire safety for our nations’
critical infrastructures.
COMPUTATIONAL FLUID DYNAMICS
Computational Fluid Dynamics (CFD) research in the MAE department includes the development of spatially and temporally high-order accurate schemes to perform
Reynolds Average Navier-Stokes (RANS), Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS) of
complex flows on massively parallel supercomputers.
Imaged-based Patient-Specific Blood Flow Modeling (Meng)
To enable clinicians to make scientifically sound clinical decisions on diagnosis and treatment of vascular
diseases, we need to develop anatomically realistic patient-specific models. Using computerized image processing, scientific visualization and CFD that are based on a patient’s medical images and other
data, a realistic model of the three-dimensional vessel geometry and the blood flow field can be built for each patient. The computational model can further incorporate various “virtual interventions” to
predict the hemodynamic and biological response, thus helping to assess risk and recommend the most effective treatment. When the whole process is streamlined from imaging to 3D reconstruction to CFD
simulations to analysis, its impact in improving human health will be tremendous.
Modeling of Turbulent Flows (Taulbee)
In attempting to find a universal theory to predict various turbulent flows, researchers are utilizing equations involving higher-order
correlations in fluctuating velocities and pressure; hence dynamic equations for the Reynolds stresses are solved in
addition to the mean momentum equations. Improvements are sought for the closure relations for the unknown
correlations in the dynamic equations. Numerical solutions are carried out for shear flows (jets, wakes, plumes, etc.), and
comparisons are made between calculated and experimental results to verify the closure hypothesis.
Fluid-Structure Modeling of Composite Structure Response from a Fire (DesJardin)
Up to 60% of the total heat transfer in a hydrocarbon fire comes from thermal radiation. The radiation heat
transfer can cause significant degradation of structural integrity and ultimately material failure. The focus of this research is to model the
response of composite structures from a pool fire. The activities include development of a thermo-mechanical damage model for composite
materials, a near-wall turbulence model for wall fires, and numerical algorithms to couple CFD and FEM based solid mechanics codes together using
level set methodologies. The ultimate goal of this effort is to predict failure of a composite structure from a fire.
Turbulence-Chemistry Interactions in Reactive Turbulent Shear Flows (Madnia)
Since the mean shear is present in most of the turbulent flows, the study of homogeneous shear flows can
reveal many features of compressibility in practical turbulent flows. The influence of chemical reaction
on the development of compressible turbulent shear flows is being studied by solving the Navier-Stokes
equations, the energy equation, and the transport equations for the reactive scalars.
Turbulent Transport and Modeling of a Passive Scalar in Grid Turbulence (Madnia)
Numerical simulations are conducted to study the structure and development of the scalar wake produced by a
single line source in decaying isotropic turbulence. The structure of the scalar wake will be studied by analyzing
each term in the transport equations for scalar moments. This is particularly useful for assessing the behavior and
predictions of different turbulent closures.
THERMAL/CHEMICAL/MECHANICAL SYSTEMS MODELING
Often, engineering systems are composed of a combination of subsystems or phenomena whose individual behaviors are fairly well understood while the interactive
combination that defines the system is not. In approaching such problems, the physics of each subsystem and the ability to model and compute its behavior is first established. Then the interfaces between the subsystems are
similarly investigated. Finally, a complete model and computational approach are established. Often, the level of detail in the model and the ability to compute the resulting equations must be weighed against each other.
Performance of a High-Pressure Safety Relief Valve(Felske)
Safe storage of gases in tanks at high pressures requires a valve to relieve unexpected pressure excursions. One
design involves a spindle moving in a bore in the valve body, which seals at design pressure and rapidly opens with
over-pressure. Gas dynamic behavior (including transient wave/shock structures) accelerates the spindle upon opening
such that it reaches a high velocity (~15m/s) before impacting a shoulder that protrudes into the bore. Plastic
deformation of the shoulder and the spindle occurs, sometimes to an extent where the valve is rendered nonfunctioning.
The research involves modeling the combined gas dynamics/solid mechanics behavior such that modifications to
the spindle/shoulder materials and contact geometry result in a more robust design.
Modeling the Stress/Deformation/Thrust Behavior of High-Performance Swimming Fins (Felske, Mollendorf, Pendergast)
Theoretical and numerical analyses are being performed of the stress, deformation, and thrust produced in high-performance swim fins under the pressure forces developed
during use. This is a problem involving coupled fluid-structure behavior in which the deformation of the solid can be
very large and hyperelastic. The analytical/numerical results are being compared with data recently acquired at the
Center for Special Environments.
Multi-Recompression Heater (MRH; Felske, Lordi, Mollendorf)
The MRH is a rotary mechanical device designed to cleanly heat a gas stream by compression to a few
thousand degrees Kelvin. The MRH has potential application to a number of environmental problems, including the
destruction of hazardous chemicals and the formation of chemicals with minimal waste. In these chemical
applications, pyrolisis rather than combustion is utilized, thereby avoiding the unwanted reaction products attendant to
combustion. Also, being a compression process, it has the advantage of a more uniformly heated stream. The next step in
our research is to complete the detailed design, fabrication, and testing of a demonstration device: 100 horsepower,
2 atm outlet pressure, 6 _ rotor diameter and length, 10,800 RPM, 0.1 lbm/sec argon flow, with an outlet
temperature of 2000K. Presently being considered are the thermal/mechanical issues: materials selection, bearing
design, thermoelastic behavior, stress levels, and cooling requirements. Measurements of compressive heating are
being made on a Roots blower. Theoretical studies have focused on the key issues of heat transfer, structural
properties, clearances, and the detailed gas dynamics of leakage flows.
PARTICULATE LIGHT SCATTERING
The scattering of light is ubiquitous in nature (blue sky) and in scientific and engineering systems. Sometimes particles are artificially introduced into a fluid to
produce a desired effect (flow visualization). Other times, such as in fuel-rich combustion, particles occur naturally and may be either desirable (production of carbon black) or undesirable (soot in diesel exhaust). In all
cases, manipulation of process variables to enhance the desired effect needs to be monitored. The most effective way to do this is noninvasively, by light scattering. Serious difficulties in interpreting the measurements
stem from the complex shape and composition of the particles.
The research is mostly concerned with the application of theory of dynamical systems to the problems of stability and transition phenomena in fluid dynamics, such as the
viscous and inviscid stability problem in a compressible boundary layer, the interaction of shock waves, and the
structure of the Mach stems. These problems will be reduced or approximated by a low-order dynamical system.
Bifurcation and their stability will then be investigated.
Boundary Layer Separation
Solutions of Prandtl's boundary layer equations near the point of separation are studied. The question of existence and uniqueness are investigated.
Simple models will be constructed to exhibit the separation phenomena. Numerical methods will be established to solve
the boundary layer continuation problem, including the point of separation.
Stability of the Hypersonic Boundary Layer
An analytic approach to the stability analysis is developed based on the WKB method. It is applicable to both insulated walls or walls with heat transfer. Using this model, it is also possible to extend the
analysis to include the effects of pressure changes, such as in a corner.
Nonlinear Response of Hysterically Damped Systems Dampers
These are known to be very effective devices in earthquake engineering. By using nonlinear dynamic system methods, such as the averaging method, the response of hysterically damped systems is analyzed, with emphasis on
base isolation systems. This will render a more effective nonlinear model for practical engineers.
EXPERIMENTAL FLUID MECHANICS
Many applications in mechanical and aerospace engineering involve aspects of fluid mechanics. Experimental investigations of both
fundamental and applied fluid mechanics problems yield new information on important physics that can be used to design and improve real
engineering systems. Both traditional instrumentation (e.g. hot-wire anemometry, laser Doppler anemometry, pitot probes, schlieren flow
visualization, thermocouples) as well as modern diagnostics (stereoscopic/holographic particle image velocimetry, laser induced fluorescence)
will be used to explore problems of current interest. A thorough understanding of experimental design, uncertainty analysis, digital signal
processing, and instrumentation is required to effectively conduct experimental research. Current interests include: fundamentals of turbulent
shear flows, boundary layer separation, stability transition and bifurcation, flow control, aero-acoustics, compressible flow, reacting flow, and
multi-phase flow. Collaboration with researchers in the areas of computational and theoretical fluid dynamics will help maximize scientific and
engineering contributions. Emphasis is maintained on understanding physical processes involved in a wide range of fluid mechanics applications.
