Near-Field Flow Visualization of Vortex Generator Jets

Experimental investigation on flow visualization of a single pitched and skewed jet in crossflow was conducted by Prof. Compton and her graduate student John Stadnicki. To capture still images of a cross-section of the et flow, alight sheet formed by a pulsed Nd: YAG laser was used to illuminate smoke-tagged jet fluid. Through still images, they monitored the instantaneous location and structure of the jet fluid. By averaging still images, they compare the instantaneous structure to the mean flow field.

Faculty:
Prof. Debora Compton

Students:
John Stadnicki

Publications

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Use of Conventional Fluid Dynamics to Predict Sound Generated by Complex Flows

The research will enable the acoustic portion of a complicated flow field to be identified as a subsequent step in a CFD calculation even if the original calculation is only valid for incompressible flow. This method is called the acoustic projection method. The fundamental idea is not new in the sense that some researchers currently use methods based on Lighthill's acoustic analogy, take fluid dynamic results, and from them calculate, the sound radiated by the flow. However, the method used in this research allows the acoustics to be identified within the region containing the complex flow as opposed to only outside this region. Also, the outcome of this research will be a computational supplement to CFD codes which can be easily used and understood by those who are not experts in acoustics.

Faculty:
Prof. Sheryl Grace; Prof. Allan Pierce; Christophe Bailly (Ecole Central De Lyon, Lyon France)

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Panel Method Based Prediction of Sound Generated by a Multi-Element High-Lift Wing Section

The research provides a prediction tool for airframe noise generated by high-lift wing configurations. The goal of the project is to develop a design tool which will capture the important acoustic production mechanisms without fully modeling the viscous nonlinear fluid dynamics existing near a high-lift wing. The mechanisms which will be modeled include the oscillation of the vortex core which forms in the cove under the slat and the main airfoil element, the forced unsteady flow through the slat gap which interacts with the slat tracks, the upstream airfoil element wakes which convect past the downstream airfoil elements and induce fluctuating surface forces, and the vorticity created at side edges.

The prediction tool will consist of an unsteady panel method for calculating the unsteady aerodynamic forces coupled to an acoustic propagation model. The method will enable simultaneous aerodynamic and acoustic analysis of high-lift systems to be completed in a short time on a modern work station. Moreover, external forces such as ground effect can be included quite simply into the model.

Faculty:
Prof. Sheryl Grace; Prof. Luigi Morino (Univ. of Rome)

Students:
Trevor Wood

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Rayleigh Conductivity

Use of the Rayleigh conductivity parameter for analyzing low mach number high Reynolds number flow past wall openings and wall apertures. The analysis is used to determine frequency ranges in which unsteady disturbances will be amplified or absorbed by the shear layer which forms in the mouth of the wall opening.

Faculty:
Prof. Sheryl Grace; Prof. Michael Howe

Students:
Trevor Wood, Kelly Horan (former)

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The Aeromechanical Effect of Vane Clocking in Turbines

This research will evaluate and improve existing methods for predicting multi-stage effects in turbines. The evaluation will be based on comparisons of the computational predictions and previously obtained experimental data. Until this time, most multi-stage studies focused on the optimization of efficiency. In this research, the emphasis will be on the prediction of the unsteady blade loading. Once a valid unsteady aerodynamic prediction tool is identified, it will give General Electric Aircraft Engineering a method for determining the indexing which will simultaneously provide best efficiency and reduction of blade fatigue.

Faculty:
Prof. Sheryl Grace

Students:
Ruby Zenon

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Inverse Problem in Aeroacoustics & Unsteady Aerodynamics

Traditionally, in studying aerodynamically generated sound, one first identifies and quantifies the sources of sound and then calculates the scattered sound. This direct approach has been used to study sound generated by incident acoustic and vortical disturbances or turbulence interacting with a body as well as sound from jets.

In this research, we developed an inverse approach for the aeroacoustic problem of a streamlined body in a subsonic mean flow. The radiated sound is generated as a result of either the oscillatory motion of the body or the interaction of incident acoustic or vortical waves with the body. Our development of the inverse approach mirrors the development of the direct problem. We consider the case of a 2-D flat-plate airfoil and a 3-D rectangular wing in unsteady subsonic flow. We have demonstrated the feasibility of performing the aeroacoustic inversion for both of these cases.

Faculty:
Prof. Sheryl Grace

Students:
Trevor Wood

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Volume and Rigidity of the Corpera Cavernosa

Use of fluid dynamics (hemodynamics) and structural mechanics to study male impotence as a function of geometry, intracavernosal pressure and cavernosal as well as tunical material properties. Theoretical determination of penile buckling forces and non-invasive determination of cavernosal tissue fibrosis.

Faculty:
Prof. Daniel Udelson

Students:
Richard Terry(former), James L'Esperance (former), Christopher Arend (former), Daniel Sciortino (former), Justin Chavez and Haibiao Luo.

Related Projects:
Clitoral and Vaginal Mechanics
Corporal veno-occlusion

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Flow-Structure Interaction Noise Predicted from RANS (Reynolds Average Navier-Stokes) Computations of the Blocked Wall Pressure

Use of fluid dynamics (hemodynamics) and structural mechanics to study male impotence as a function of geometry, intracavernosal pressure and cavernosal as well as tunical material properties. Theoretical determination of penile buckling forces and non-invasive determination of cavernosal tissue fibrosis.

Faculty:
Prof. Michael Howe

Related Projects:
A New Approach to 2-D LAS Simulation of Aerodynamic Flow

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Vibration Damping of Flaps and Airfoils

Faculty:
Prof. Michael Howe

Related Projects:
Non-Equilibrium Modeling of Complex Turbulent Flows

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Nonlinear Waves in Bubbly Liquids

Even when present at volume fractions of less than one percent, gas bubbles in a liquid have a strong effect on the propagation, scattering and attenuation of sound in the medium. This is important in ocean acoustics since the region near the ocean surface has a substantial gas content, entrained by the breaking of surface waves. We are interested in sound propagation in bubbly liquids, particularly at frequencies which are near the resonant frequency of individual bubbles at which nonlinear effects become significant. We have identified a novel equation-of-state which relates the pressure in the bubbly mixture to the density and its first and second time derivatives. With this as a starting point, we are currently analyzing a number of linear and nonlinear wave propagation problems in bubbly liquids.

Faculty:
Prof. Ali Nadim; Prof. Paul Barbone; Prof. Daniel Goldman (Johns Hopkins University)

Students:
Jerome Cartmell

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Nonlinear Oscillations of Gas Bubbles in Acoustic Fields

In this study, we consider the detailed interaction between sound waves and small groups of gas bubbles. For the case of a single bubble in an oscillatory pressure field, we have been able to improve Blake's static threshold for acoustic cavitation to account for nonlinear dynamic effects. We are now examining the coupling between breathing and shape modes in a single bubble, as well as the interaction between two bubbles in a sound field. By doing so, we hope to extend what is currently known about so-called primary and secondary Bjerknes forces (which respectively model the force arising on a bubble in a oscillatory pressure gradient and that between two oscillating bubbles) into the nonlinear regime.

Faculty:
Prof. Ali Nadim; Prof. Tasso Kaper (Math Dept. Boston University)

Students:
Anthony Harkin

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Effects of Surfactants on Shape Oscillations of Drops and Bubbles

When surfactants are present at an interface, they tend to lower the surface tension and impart rheological properties (e.g., surface viscosity) to the interfacial layer. In this work, we examine the effects of surfactants on the shape oscillations of liquid drops and gas bubbles. A principal goal is to obtain analytical results for the enhanced damping rate of small amplitude shape modes, due to surfactant diffusion and Marangoni effects, together with surface shear and dilatational viscosity. At the same time, we study large amplitude oscillations of drops and bubbles using the Boundary Integral Method for potential flow. We have extended this numerical method to include the effects of surfactant transport and interfacial rheology. Also, although the method is primarily applicable to potential flows, we have found a way to include weak viscous effects from the bulk fluid phases.

Faculty:
Prof. Ali Nadim

Students:
Brian Rush

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Dynamics of Chains of Particles in Magnetic Fluids

An important mechanism in MagnetoRheological (MR) and ElectroRheological (ER) Fluids is the formation of particle chains when an external magnetic or electric field is applied. These chains are considered to be the primary entities which modify the rheological behavior of the fluid in the presence of the field, enhancing its viscosity by several orders of magnitude. We have been studying the dynamics of such chains at a fundamental level, starting with the dynamics of two permanent or induced dipoles in a rotating magnetic field, in which we take complete account of hydrodynamic interactions between the particles. We are also devising ways to simulate the dynamics of longer chains through pairwise additivity of hydrodynamic interactions.

Faculty:
Prof. Ali Nadim

Students:
Kathleen Mahoney (former)

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Volume-of-Fluid Method for Simulating Flows with Interfaces

The volume-of-fluid (VOF) method is a useful numerical tool for studying flows of immiscible fluids with interfaces and capillary effects. In VOF, a fixed Cartesian grid is used and the interface is localized by means of a volume-fraction field which provides the fraction of each computational cell which is occupied by one of the two phases. Surface tension effects are incorporated by smearing the capillary stresses as a body force acting over a small number of cells surrounding the interface. We are currently using this method to simulate the compressible collapse of a nonspherical gas bubble, trying to assess the relative importance of shock versus jet formation in sonoluminescence. We are also developing ways to combine with VOF method with "level-sets" in order to achieve a more accurate representation of curvature.

Faculty:
Prof. Ali Nadim; Prof. Stephane Zaleski (University of Paris 6); Prof. Hossein Haj-Hariri (University of Virginia)

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Dynamics & Rheology of Complex Fluids

The field of Complex Fluids encompasses such multiphase systems as suspensions, emulsions, polymeric solutions, colloids, ferrofluids, electrorheological (ER) fluids and the like. These systems are characterized by the existence of complex microstructural elements which are suspended in a liquid host. The microstructural entities may be orientable and/or deformable and their dynamics and interactions are determined by hydrodynamic, electrostatic, magnetic, elastic, interfacial and Brownian forces. Our studies of such systems focus on modeling the detailed dynamics of the microstructure and on determining the macroscopic (rheological) behavior of the complex fluid they're from. We are currently interested in time-dependent flows of polymer solutions (modeled as elastic dumbbells), of microemulsions with surfactants and interfacial rheology, and of colloidal magnetic fluids (ferrofluids).

Faculty:
Prof. Ali Nadim; Prof. Howard Brenner (Massachusetts Institute of Technology); Prof. Daniel Lhuillier (University of Paris 6)

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Integrated Plasma Deposition Processing for Advanced Control of Coating Structure

Plasma spray deposition is a process used to deposit metal or ceramic coatings for thermal or corrosion protection, with applications to jet engine components and fuel cells. The process features complex plasma/particle and particle/substrate interactions, which involve significant distributions and variations. The research is focused on understanding the sources of these distributions and their effect on coating quality, and using this knowledge base to mitigate these effects through development of an intelligent control system. This requires a deeper understanding of the fundamental processing/structure relationships, which are studied using a combined experimental and modeling approach.  A major focus of the research is on the development of new sensing capabilities to more effectively study the fundamental processing/structure relationships and to enable feedback control schemes that exploit those relationships.  This work is funded by NSF.

Professors: M. Gevelber, D. Wroblewski, S. Basu
Students: M. Van Hout (MS), D. Willoughby (MS)

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Refractive and clear air turbulence in the upper troposphere and lower stratosphere

Turbulence in the Upper Troposphere and Lower Stratosphere (UTLS) can adversely impact performance of a range of aerospace systems; optical Turbulence (OpT) from fluctuations in temperature and humidity can disrupt communications, radar, and high energy laser systems and Clear Air Turbulence (CAT) can lead to aircraft upset. The main thrust of this project is characterization and analysis of turbulent layers in the stably stratified regions of UTLS, using high resolution turbulence data collected from Air Force sponsored aircraft measurement campaigns.  The research includes the study of layer formation and evolution, analysis of statistical descriptors of the flow, such as structure functions, and the identification and characterization of coherent structures.  The work also involves collaboration with Direct Numerical Simulation (DNS) researchers, to provide insights that can’t be gleaned from measurements or DNS alone, and to aid in validation of the simulations.  This work is funded by AFRL.

Professors:      D. Wroblewski
Collaboraters:  O. Cote (AFRL), J. Hacker (Flinders University, Australia), R. Dobosy (NOAA), J. Werne (NWRA/CORA).

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