Laboratory for Turbulence and Complex Flow

Department of Mechanical Science and Engineering
University of Illinois at Urbana-Champaign

Current Research

Turbulence

Realistic Roughness Effects in Wall Turbulence

Ph.D. Student: Yanhua Wu

Master’s Students: Blake Johnson and Adam Rosenbaum

Funding: Core and DURIP grants from the Air Force Office of Scientific Research (Dr. John Schmisseur, Program Manager).

Synopsis: Realistic roughness refers to highly-irregular roughness patterns created by damage to a flow surface through scratching, pitting and/or deposition of contaminants.  Although the influence of both discrete and distributed roughness on the character of wall-bounded flows has been studied extensively in the past, recent research indicates that these “simulated” roughness conditions are not representative of the influence of realistic roughness.  To this end, surface profiles from damaged turbine blades are replicated in a flat-plate turbulent boundary layer in order to document their effect on the behavior of wall turbulence.

Publications: Wu, Y. & Christensen, K. T.  2010.  Spatial Structure of a Turbulent Boundary Layer with Irregular Surface Roughness. J. Fluid Mech., 655, 380-418.

Mejia-Alvarez, R., Wu, Y. & Christensen, K. T. 2009. Modifications of the Structure of Turbulent Flow by a Rough Surface. 47th AIAA Aerospace Sciences Meeting, AIAA Paper 2009-0399.

Wu, Y. & Christensen, K. T. 2008. Structural Characteristics of Flow Over a Highly-Irregular Surface Topography. 46th AIAA Aerospace Sciences Meeting, AIAA Paper 2008-0648.

Wu, Y. and Christensen, K. T. 2007. Turbulence Modifications in the Roughness Sublayer of Flow over a Highly-Irregular Surface Topography. 37th AIAA Fluid Dynamics Conference, AIAA Paper 2007-3995.

Wu, Y. and Christensen, K. T.  2007.  Outer-Layer Similarity in the Presence of a Practical Rough-Wall Topography. Phys. Fluids 19 (8), 085108..

Wu, Y. and Christensen, K. T. 2007. The Validity of Outer-Layer Similarity in the Presence of Highly-Irregular Surface Roughness. 45th AIAA Aerospace Sciences Meeting, AIAA Paper 2007-0528.

Wu, Y. and Christensen, K. T.  2006.  Reynolds-Stress Enhancement Associated with a Short Fetch of Roughness in Wall Turbulence.  AIAA J. 44 (12), 3098-3106.

Wu, Y., Natrajan, V. and Christensen, K. T.  2006.  Reynolds-Stress Enhancement Associated with a Short Fetch of Roughness in Wall Turbulence.  44th AIAA Aerospace Sciences Meeting, AIAA Paper 2006-1117.


Low-Order Models of Highly-Irregular Surface Roughness in Wall Turbulence

Ph.D. Student: Ricardo Mejia-Alvarez

Master’s Students: Blake Johnson

Funding: Young Investigator Award from the Air Force Office of Scientific Research (Dr. John Schmisseur, Program Manager).

Synopsis: The research described above is extended by considering the development of low-order models of highly-irregular surface topologies commonly encountered in practical wall-bounded turbulent flows. The goal is to develop simpler representations of these topologies, which can contain beyond 100 topologically-relevant scales, that mimic the overall impact of the complete surface on the flow. These simplified surfaces could then be used in realistic large-eddy or direct numerical simulations of these complex flows. In this regard, we hope to develop a general methodology for identifying a subset of the full topological scales that generate the most significant impact in the flow.

Publications: Mejia-Alvarez, R. & Christensen, K. T.  2010.  Low-Order Representations of Irregular Surface Roughness and Their Impact on a Turbulent Boundary Layer. Phys. Fluids, 22 (1), 015106 (20 pp).

Johnson, B. & Christensen, K. T.  2009.  Turbulent Flow Over Low-Order Models of Highly-Irregular Surface Roughness. AIAA J., 47 (5), 1288-1299.

Johnson, B. & Christensen, K. T.  2009.  Turbulent Flow Over Low-Order Models of Highly-Irregular Surface Roughness. AIAA J., 47 (5), 1288-1299.

Johnson, B. & Christensen, K. T. 2008. Low-Order Models of Highly-Irregular Surface Roughness. 38th AIAA Fluid Dynamics Conference, AIAA Paper 2008-3961.


Outer-Layer Structure in Wall Turbulence

Ph.D. Students: Yanhua Wu and Vinay Natrajan

Funding: Core and DURIP grants from the Air Force Office of Scientific Research (Dr. John Schmisseur, Program Manager) and the University of Illinois.

Synopsis: Instantaneous, high-resolution velocity field measurements have been made in the streamwise-wall-normal plane of turbulent channel flow and a zero-pressure-gradient turbulent boundary layer over a broad Reynolds-nunber range using particle-image velocimetry (PIV). These extensive datasets are used to study the underlying characteristics of hairpin vortices and hairpin vortex packets that densely populate the outer layer of wall turbulence. Of particular interest are the population trends of the individual hairpin structures both with Reynolds number and wall-normal position, the average spatial characteristics of the larger-scale vortex packets and the role played by these structures in subgrid-scale modeling for large eddy simulation (LES) of wall turbulence. In addition, the existence of spanwise vortices with rotation counter to that of the hairpin heads is studied with particular interest in understanding their origin as well as how they might be related to the hairpin packet model of the outer layer.

Publications: Natrajan, V., Wu, Y. & Christensen, K. T. 2007. Spatial Signatures of Retrograde Spanwise Vortices in Wall Turbulence. J. Fluid Mech. 574, 155-167.

Wu, Y. & Christensen, K. T. 2006. Population Trends of Spanwise Vortices in Wall Turbulence. J. Fluid Mech. 568, 55-76.

Natrajan, V. & Christensen, K. T. 2006. The Role of Coherent Structures in Subgrid-Scale Energy Transfer Within the Log Layer of Wall Turbulence. Phys. Fluids 18 (6), 065104.


Heated Jets in Cross-Flow

Collaborators: Prof. Greg Elliott (Aero., Illinois) and IllinoisRocstar LLC

Ph.D. Student: Blake Johnson

Funding: STTR Grant through the Office of Naval Research

Synopsis: Existing research on the behavior of jets in cross flow has focused primarily on transport of momentum in the case of the unheated (isothermal) plume. Natural and engineering phenomena such as dispersion of volcanic plumes and the emission of exhaust gases into cross-winds inspire research of thermal and momentum transport of heated jets in cross flow. Wind-tunnel tests are performed using a rake of thermocouples and Pitot-static probes to measure temperature and velocity fields in both the near- and far-field regions of heated plumes. A number of flow parameters are studied including temperature ratio, velocity ratio, flush/raised stack geometry, circular and rectangular jets, rectangular stack aspect ratio and orientation relative to cross-flow, and the behavior of arrays of multiple rectangular stacks. PIV measurements will also be made to investigate the onset of dominant far-field flow structures and the turbulent interaction of the jet with the cross-stream in the near-field region. All data is utilized to validate LES computations performed by IllinoisRocstar LLC for equivalent configurations.

Publications: Johnson, B., Elliott, G. & Christensen, K. T. 2009. An Experimental Study of a Heated Circular Stack Emitting into a Crossflow. 39th AIAA Fluid Dynamics Conference, AIAA Paper 2009-4171.


Polymer-Induced Turbulence Modifications in Impinging Jets

Master’s Student: Ricardo Mejia-Alvarez

Funding: The University of Illinois

Synopsis: Impinging jets are of enormous engineering interest because of their occurrence in a broad range of technologically-relevant applications, including cooling, heating and drying operations, drilling, cutting, mixing and fire-fighting.  The present effort attempts to assess the turbulence modifications imposed in this flow configuration via the addition of a minute amount of polymer to the flow.  In particular, any alterations of the complex vortex interactions that are observed in the impingement zone of Newtonian impinging jets will be studied as well as any convective heat-transfer enhancement that might be garnered in this region through the addition of polymer. These goals are accomplished via detailed PIV experiments of the flow within the impingement zone at low and high Reynolds numbers, various nozzle-to-plate spacings and multiple polymer concentrations.  Simultaneously, a constant heat flux is applied to the impinging surface and instantaneous fluid temperature fields are acquired over the same field of view in the impingement zone using laser-induced fluorescence (LIF) techniques.

Microscale Fluid Mechanics

Development of Velocity and Temperature Measurement Methods for Complex, Three-Dimensional Microvascular Networks

Ph.D. Students: Vinay Natrajan and Rajat Saksena

Funding: A MURI Grant from the Air Force Office of Scientific Research (Prof. Scott White, PI; Dr. Les Lee, Program Manager) and a gift from the MechSE Kritzer Fund at Illinois.

Synopsis: Microscopic particle-image velocimetry is being adapted to the study of flow within three-dimensional microvascular systems.  In addition, a laser-induced fluorescence method for measuring temperature fields in microfluidic systems is being developed and applied to assess the cooling capabilities of such systems.  This work is part of a larger effort in the development of self-healing and self-cooling composite materials using complex microvascular networks.

Publications: Kozola, B. D., Shipton, L. A., Natrajan, V. K., Christensen, K. T. & White, S. R. 2010. Characterization of Active Cooling and Flow Distribution in Microvascular Polymers. Journal of Intelligent Material Systems and Structures, in press.

Natrajan, V. K. and Christensen, K. T.  2009.  Two-Color Laser-Induced Fluorescent Thermometry for Microfluidic Systems. Meas. Sci. Tech. 20 (1), 015401 (11pp).

Natrajan, V. K. & Christensen, K. T. 2008. Fluorescent Thermometry. In Encyclopedia of Microfluidics and Nanofluidics, D. Li (ed.), Springer-Verlag (New York, NY), pp. 750-759.

Natrajan, V. K. & Christensen, K. T. 2008. Methods for Temperature Measurement. In Encyclopedia of Microfluidics and Nanofluidics, D. Li (ed.), Springer-Verlag (New York, NY), pp. 1994-2005.

Natrajan, V. K. & Christensen, K. T. 2008. A Two-Color Fluorescent Thermometry Technique for Microfluidic Devices. 46th AIAA Aerospace Sciences Meeting, AIAA Paper 2008-0689.

Yamaguchi, E., Natrajan, V. and Christensen, K. T. 2006. Development of a Two-Dye LIF Technique for Measuring Fluid Temperature Fields in Microfluidic Devices. ASME Joint U.S.-European Fluids Engineering Summer Meeting, ASME Paper FEDSM2006-98128.


The Structure of Transition and Turbulence in Wall-Bounded Flows at the Microscale

Ph.D. Student: Vinay Natrajan

Funding: University of Illinois.

Synopsis: Microscopic particle-image velocimetry is utilized to study the structure of transition and turbulence in 500-micron glass capillaries.  High-resolution, instantaneous velocity measurements are made in the streamwise-wall-normal plane of the capillary over a broad Reynolds number range (1800 < Re < 4500) to study the structural phenomenology of transition and turbulence at the microscale. Measurements at the highest Reynolds number are compared to a direct numerical simulation of turbulent pipe flow at Re = 5300 to establish the efficacy of microscopic PIV in resolving the relatively small instantaneous velocity fluctuations that exist in such flows.

Publications: Natrajan, V. K. & Christensen, K. T.  2010.  The Impact of Surface Roughness on Flow Through a Rectangular Microchannel from the Laminar to Turbulent Regimes. Microfluid. Nanofluid., in press. 

Natrajan, V. & Christensen, K. T. 2009. Structural Characteristics of Transition to Turbulence in Microscale Capillaries. Phys. Fluids, 21 (3), 034104 (19 pp).

Natrajan, V. K. & Christensen, K. T. 2008. Structural Characteristics of Transitional Capillary Flow. 38th AIAA Fluid Dynamics Conference, AIAA Paper 2008-4277.

Natrajan, V. & Christensen, K. T. 2007. Microscopic Particle Image Velocimetry Measurements of Transition to Turbulence in Microscale Capillaries. Exp. Fluids 43(1), 1-16.

Natrajan, V. K. & Christensen, K. T. 2007. A Microscopic Particle Image Velocimetry Study of Transition to Turbulence in Microscale Capillaries. 37th AIAA Fluid Dynamics Conference, AIAA Paper 2007-3990.

Natrajan, V., Yamaguchi, E. & Christensen, K. T. 2007. Statistical and Structural Similarities Between Micro- and Macro-Scale Wall Turbulence. Microfluidics and Nanofluidics 3 (1), 89-100.


Studies of Thermal Transport Through Smooth- and Rough-Wall Microchannels

Ph.D. Student: Vinay Natrajan

Funding: University of Illinois.

Synopsis: Using a recently-developed non-invasive fluorescent thermometry method for fluid-temperature measurement in microfluidic devices, the physics of thermal transport is studied in smooth- and rough-wall microchannels over a broad Reynolds-number range spanning the laminar, transitional and turbulent flow regimes. The goal of this effort is to carefully document the average Nusselt-number behavior across these flow regimes for smooth-wall flow at the microscale and contrast it with well-accepted heat-transfer correlations developed from macroscale experiments. Our goal is to then assess the impact of surface roughness on this baseline smooth-wall behavior.

Publications: Natrajan, V. K. and Christensen, K. T.  2010.  Non-Intrusive Measurements of Convective Heat Transfer in Smooth- and Rough-Wall Microchannels: Laminar Flow. Exp. Fluids, in press. 

Natrajan, V. K. and Christensen, K. T.  2010.  Non-Intrusive Measurements of Convective Heat Transfer in Smooth- and Rough-Wall Microchannels: Transitional and Turbulent Flow. Exp. Fluids, submitted.

Natrajan, V. K. & Christensen, K. T. 2009. Studies of Flow and Heat-Transfer in Smooth- and Rough-Wall Microchannels. ASME International Mechanical Engineering Congress & Exposition, IMECE2009-12190.

Natrajan, V. K. & Christensen, K. T. 2009. An Experimental Study of Thermal Transport in Transitional Flow Through Rough-Wall Microchannels. 39th AIAA Fluid Dynamics Conference, AIAA Paper 2009-3584.

Natrajan, V. K. & Christensen, K. T. 2009. An Experimental Study of Thermal Transport in Transitional Flow at the Microscale. 47th AIAA Aerospace Sciences Meeting, AIAA Paper 2009-1123.


Biological Fluid Mechanics

Experimental Studies of Flow Within a Pediatric Ventricular Assist Device

Co-PI’s: Drs. I. Cestari and M. Muramatsu (Univ. Sao Paulo, Brazil)

Visiting Ph.D. Student: Eduardo Ferrara (Univ. Sao Paulo, Brazil )

Funding: The University of Illinois and the Sao Paulo State Foundation for the Support of Research.

Synopsis: Cardiac transplantation is a well-established treatment option for patients with heart failure and ventricular assist devices (VAD's) serve a vital role as a bridge to transplantation.  However, the design of pediatric and neonatal VAD’s is complicated by the small dimensions of the devices and higher beating frequencies that can increase the occurrence of thrombosis and hemolysis.  Prototype pediatric and neonatal VAD’s have been designed at the University of Sao Paulo and a parameter-space study of the flow within these devices is being pursued using PIV.  The goal is to identify flow behavior that can lead to thrombosis and hemolysis.  This work is a collaboration with the Bioengineering Division of the University of Sao Paulo in Brazil .

Publications: Ferrara, E., Muramatsu, M., Christensen, K. T. and Cestari, I. A.  2010.  Particle-Image Velocimetry Study of a Pediatric Ventricular Assist Device. ASME J. Biomech. Eng., 132 (7), 071004 (6 pp).

Christensen, K. T., Ferrara, E., Muramatsu, M. & Cestari, I. A. 2005. The Influence of Beating Frequency on the Flow Within a Pediatric Ventricular Device.6th International Symposium on Particle Image Velocimetry.

Christensen, K. T., Ferrara, E., Muramatsu, M. & Cestari, I. A. 2005. PIV Study of Flow Within a Pediatric Ventricular Assist Device. 35th AIAA Fluid Dynamics Conference, AIAA Paper 2005-5003.

©2008 Laboratory for Turbulence and Complex Flow

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