Research

Research by graduate students, postdoctoral researchers, research scientists, and faculty in LTC focuses on fundamental studies of fluid dynamics, turbulent flows, combustion, and advanced microsystems for flow and combustion applications. Listed below are some of the major research projects that have recently been conducted in LTC and a brief summary of each project. To obtain more information about any of these projects and the technical results obtained from them, consult the publications listed for each project and the associated doctoral dissertations.

Experimental Studies of Turbulent Shear Flow Properties via Dual-Plane Stereo PIV

Development and application of a new dual-plane stereo PIV (DSPIV) measurement technique is providing the first direct noninvasive experimental access to the full velocity gradient tensor fields at the intermediate and small scales of turbulent flows. DSPIV is based on two sets of independent stereo PIV measurements of all three velocity components in two thin, parallel, differentially-spaced light sheets with different frequencies. Interest in this study is in the quasi-universal scales of turbulent shear flows at high Reynolds numbers.

Mullin, J.A. & Dahm, W.J.A. (2006) Dual-plane stereo particle image velocimetry measurements of velocity gradient tensor fields in turbulent shear flow. Part 1: Accuracy assessments. Physics of Fluids Vol. 18 (3): Art. No. 035101, March 2006.

Mullin, J.A. & Dahm, W.J.A. (2006) Dual-plane stereo particle image velocimetry measurements of velocity gradient tensor fields in turbulent shear flow. Part 2: Experimental results. Physics of Fluids Vol. 18 (3): Art. No. 035102, March 2006.

Mullin, J.A. and Dahm, W.J.A. (2005) Dual-plane stereo particle image velocimetry (DSPIV) for measuring velocity gradient fields at intermediate and small scales of turbulent flows. Experiments in Fluids, Vol. 38, pp. 185-196.

Mullin, J.A. & Dahm, W.J.A. (2004) Direct assessments of multifractal scale-similarity in true dissipation and enstrophy fields from dual-plane stereo PIV (DSPIV). In Proceedings of the 10th European Turbulence Conference ( ETC -10), 29 June - 2 July, 2004, Trondheim, Norway.

Mullin, J.A. & Dahm, W.J.A. (2004) Direct experimental measurements of velocity gradient fields in turbulent flows via high-resolution frequency-based dual-plane stereo PIV (DSPIV). In Proceedings of the 12th International Symposium on Applications of Laser Techniques to Fluid Mechanics, July 12-14, 2004 , Lisbon , Portugal .

Mullin, J.A. and Dahm, W.J.A. (2003) Dual-plane stereo PIV (DSPIV) measurements of the velocity gradient tensor field at the small scales of turbulent flows. In Proceedings of the Third International Symposium on Turbulence and Shear Flow Phenomena (TSFP-3), 25-27 June 2003, Sendai, Japan.

Mullin, J.A. and Dahm, W.J.A. (2002) Highly-resolved three-dimensional velocity measurements via dual-plane stereo particle image velocimetry (DSPIV) in turbulent flows. AIAA Paper No. 2002-0290, 40th AIAA Aerospace Sciences Meeting, January, 2002, Reno , NV .

A New Multifractal Subgrid Scale Model for Large Eddy Simulations Turbulent Flows

This project is developing a new approach to subgrid scale modeling for large eddy simulations, based on the multifractal structure of the enstrophy and scalar dissipation fields in high Reynolds number turbulent flows. The resulting model computes the subgrid velocities explicitly, and shows dramatically higher correlations for subgrid stresses and energy transfer than traditional models in a priori tests using DNS data, and provides excellent results in a posteriori tests when applied in an LES code.

Burton, G.C. and Dahm, W.J.A. (2005) Multifractal subgrid-scale modeling for large-eddy simulation. Part 1. Model development and a priori testing. Physics of Fluids Vol. 17 (7): Art. No. 075111, July 2005.

Burton, G.C. and Dahm, W.J.A. (2005) Multifractal subgrid-scale modeling for large-eddy simulation. Part 2. Backscatter limiting and a posteriori evaluation. Physics of Fluids Vol. 17 (7): Art. No. 075112, July 2005.

Burton, G.C., Dahm, W.J.A., Dowling, D.R. and Powell, K.G. (2002) Subgrid scale modeling based on multifractal structure of the subgrid vorticity field. In Advances in Turbulence IX, Proc. 9th European Turbulence Conference, July 2-5, 2002 , Southampton , England .

Burton , G.C., Dahm, W.J.A., Dowling, D.R. & Powell, K.G. (2002) High Reynolds number assessment of a multifractal subgrid scale model. AIAA Paper No. 2002-2961, 32nd AIAA Fluid Dynamics Conference, June 24-27, 2002, St. Louis, MO.

Burton , G.C., Dahm, W.J.A., Powell, K.G. and Dowling, D.R. (2002) A new multifractal subgrid scale model for large eddy simulation. AIAA Paper No. 2002-0983, 40th AIAA Aerospace Sciences Meeting, January, 2002, Reno , NV .

Burton, G.C., Dahm, W.J.A., Dowling, D.R. and Powell, K.G. (2000) Multifractal scale-similarity in subgrid-scale turbulence modeling. In Advances in Turbulence VIII Proc. 8th European Turbulence Conference, pp. 523-526, June 27-30, 2000 , Barcelona , Spain .

Heat Release Effects on Entrainment and Mixing in Turbulent Diffusion Flames

This study addressed differences observed due to heat release between reacting and nonreacting versions of otherwise identical shear flows under conditions for which buoyancy effects are negligible. The piecewise linear variations of temperature with mole fraction provided to a general equivalence principle by which the scaling laws for nonreacting flows can be extended to predict effects of heat release by exothermic reaction. The resulting predicted effects of heat release, in both the near and far fields, show good agreement with experimental data from both planar and axisymmetric momentum-dominated turbulent jet diffusion flames.

Diez-Garias, F.J. and Dahm, W.J.A. (2007) Effects of heat release on turbulent shear flows. Part 3. Buoyancy effects due to heat release in jets and plumes. Journal of Fluid Mechanics Vol. 575, pp. 221-255.

Dahm, W.J.A. (2007) Scaling relations forflare interactions, flame lengths, and crosslightling requirements in large flare fields. 2007 Joint American-Japanese Flame Research Committee International Symposium, 22-24 October 2007, Waikoloa, HI.

Dahm, W.J.A. (2005) Effects of heat release on turbulent shear flows. Part 2. Turbulent mixing layers and the equivalence principle. Journal of Fluid Mechanics, Vol. 540, pp. 1-19.

Diez, F.J. & Dahm, W.J.A. (2004) Improved prediction of buoyancy effects on flame length and combustion properties of flares. In Proceedings of the AFRC-JFRC 2004 Joint International Combustion Symposium, 10-13 October 2004, Maui, HI.

Dahm, W.J.A. (2001) Improved prediction of flame properties in airfuel and oxy-fuel combustion systems. Proc. 2001 Joint AFRC/JFRC/IEA International Combustion Symposium, September, 2001, Kauai , Hawaii .

Tacina, K.M. and Dahm, W.J.A. (2000) Effects of heat release on turbulent shear flows. Part 1. A general equivalence principle for nonbuoyant flows and its application to turbulent jet flames. Journal of Fluid Mechanics, Vol. 415, pp. 23 - 44.

Tacina, K.M. and Dahm, W.J.A. (1999) An equivalence principle for heat release effects in nonbuoyant turbulent shear flows and its application to turbulent jet flames. Proc. 1999 Joint Technical Meeting of the U.S. Sections of the Combustion Institute, pp. 344-347, Washington, D.C., March 14-17, 1999, The Combustion Institute, Pittsburgh.

Electrokinetic Microactuator Arrays for Drag Reduction by Active Sublayer Control

This project is developing microactuator arrays for active control of streamwise sublayer vortical structures in turbulent boundary layers for vehicle drag reduction, based on electrokinetic pumping to induce volume displacements in the sublayer under an impulsively applied electric field. Several such arrays have been fabricated from a basic three-layer design. Our current MEKA-5 is a full-scale hydronautical array with 25,600 individual electrokinetic microactuators on 350 µm spacing in a 7 x 7 cm mylar tile, with a novel unit-cell array architecture that provides dramatic reductions in both the sensor and processing requirements needed to achieve practical sublayer control on real vehicles.

Diez, F.J. and Dahm, W.J.A. (2004) Design and fabrication of unsteady electrokinetic microactuator arrays for turbulent boundary layer control. Journal of Micromechanics and Microengineering, Vol. 14, pp. 1307-1320.

Diez, F.J. and Dahm, W.J.A. (2003) Electrokinetic microactuator arrays and system architecture for active sublayer control of turbulent boundary layers. AIAA Journal, Vol. 41, No. 10, pp. 1906-1915.

Diez, F.J. and Dahm, W.J.A. (2002) Micro electro kinetic actuator (MEKA) arrays for active sublayer control of turbulent boundary layers. AIAA Paper No. 2002-0267, 40th AIAA Aerospace Sciences Meeting, January 2002, Reno , NV .

Dahm, W.J.A. and Diez-Garias, F.J. (2001) Electrokinetic microactuator arrays for sublayer control in turbulent boundary layers. Proc. 2nd Symposium on Smart Control of Turbulence, March 4-6, 2001, Tokyo, Japan.

Diez-Garias, F.J., Dahm, W.J.A. and Paul, P.H. (2000) Electrokinetic microactuator arrays for sublayer control of turbulent boundary layers. Proc. EUROMECH Colloquium 415 on Shear Flow Control, July 24 - 26, 2000, TU Berlin, Germany.

Diez-Garias, F.J., Dahm, W.J.A. and Paul, P.H. (2000) Microactuator arrays for sublayer control in turbulent boundary layers using the electrokinetic principle. AIAA Paper No. 2000-0548, 38th AIAA Aerospace Sciences Meeting, January 10 - 13, 2000 , Reno , NV .

Experimental Studies of Entrainment and Mixing in a Supersonic Turbulent Wake Flow

Experimental results have been obtained for entrainment and mixing in confined, supersonic, planar, turbulent, bluff-body wakes to clarify the generic effects of compressibility in turbulent shear flows. The principal effect in such confined wakes is found to be a local self-induced forcing where reflected expansion waves from the near-field recompression region interact with the large-scale structure of the wake. This leads to a dramatic downstream increase in the wake growth rate and entrainment rate. The presence of a subsonic upstream path at relatively low supersonic Mach numbers changes the wake scaling constants from unforced to forced incompressible values.

Nakagawa, M. and Dahm, W.J.A. (2006) Scaling properties and wave interactions in confined supersonic turbulent bluff-body wakes. AIAA Journal Vol. 44, No. 6, pp. 1299-1309.

Nakagawa, M. and Dahm, W.J.A. (2005) The virtual origin of incompressible and supersonic turbulent bluff-body wakes. AIAA Journal Vol. 43, No. 3, pp. 697-700.

Nakagawa, M. and Dahm, W.J.A. (2000) Control of entrainment and mixing in supersonic turbulent shear flows by expansion wave interactions. Proc. EUROMECH Colloquium 415 on Shear Flow Control, July 24 - 26, 2000, TU Berlin, Germany.

Nakagawa, M. and Dahm, W.J.A. (2000) Velocity measurements in the near-field of supersonic planar turbulent wakes. AIAA Paper No. 2000-2229, AIAA Fluids 2000 Fluid Dynamics Meeting, June, 2000, Boulder, CO.

Nakagawa, M. and Dahm, W.J.A. (2000) Experimental results on the near-field structure of supersonic planar turbulent wakes. AIAA Paper No. 2000-0664, 38th AIAA Aerospace Sciences Meeting, January 10 - 13, 2000 , Reno , NV .

Nakagawa, M. and Dahm, W.J.A. (1999) Compressibility effects on entrainment and mixing in supersonic planar turbulent wakes. AIAA Paper No. 99-3582, 30th AIAA Fluid Dynamics Conference, June 28 - July 1, 1999, Norfolk, VA.

Experimental Assessment of Fractal and Multifractal Scale-Similarity in Turbulent Flows

Experimental assessments of fractal and multifractal scale similarity in various fields have been obtained from fully-resolved four-dimensional spatio-temporal measurements of a turbulent flow. An objective statistical criterion based on the maximum allowable scale-to-scale variation in multiplier distributions allows accurate discrimination between multifractal and non-multifractal scaling. Results show that the scalar dissipation field clearly demonstrates a scale-invariant similarity consistent with a random multiplicative cascade process corresponding to a bilinear multiplier distribution.

Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1996) Experimental assessment of fractal scale similarity in turbulent flows. Part 1: One-dimensional intersections. Journal of Fluid Mechanics, Vol. 327, pp. 35 - 72.

Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1997) Experimental assessment of fractal scale similarity in turbulent flows. Part 2: Higher dimensional intersections and nonfractal inclusions. Journal of Fluid Mechanics, Vol. 338, pp. 89 - 126.

Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1997) Experimental assessment of fractal scale similarity in turbulent flows. Part 3: Multifractal scaling. Journal of Fluid Mechanics, Vol. 338, pp. 127 - 155.

Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1998) Experimental assessment of fractal scale similarity in turbulent flows. Part 4: Effects of Reynolds and Schmidt numbers. Journal of Fluid Mechanics Vol. 377, pp. 169 - 187.

Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1995) Experimental study of the fractal scaling properties of turbulent flows. Proceedings of the Tenth Symposium on

Turbulent Shear Flows, pp. P2.61 - P2.67, Penn State University, University Park, PA.

Diffusion Flame-Vortex Ring Interaction Under Microgravity Conditions

Flame-vortex experiments in microgravity provide a carefully controllable environment for fundamental combustion science studies on turbulent flame processes. This project has provided results for the roll-up and burning of a diffusion flame in a laminar vortex ring formed by impulsively issuing fuel from a round nozzle into an oxidizer environment, using experiments based on flame luminosity imaging (FLI) and wavelength modulation spectroscopy ( WMS ), as well as numerical simulations that augment the experimental results.

Chen, S.-J. and Dahm, W.J.A. (1998) Diffusion flame structure of a vortex ring under microgravity conditions. Proceedings of the Combustion Institute, Vol. 27, 2579-2586.

Chen, S.-J., Dahm, W.J.A. and Tryggvason, G. (2000) Effects of heat release in a reacting vortex ring. Proceedings of the Combustion Institute, Vol. 28, pp. 515-520.

Dahm, W.J.A., Chen, S.-J., Silver, J.A., Mullin, J.A. and Piltch , N.D. (2001) Mixture fraction measurements via WMS -ITAC in a microgravity vortex ring diffusion flame. To appear in Proceedings of the Combustion Institute, Vol. 29.

Chen, S.-J., Silver, J.A., Dahm, W.J.A. and Piltch , N.D. (2001) Mixture fraction measurements via WMS -ITAC in a laminar diffusion flame. To appear in Proceedings of the Combustion Institute, Vol. 29.

Chen, S.-J. and Dahm, W.J.A. (1999) Experiments on diffusion flame structure of a laminar vortex ring. Proc. 1999 Joint Technical Meeting of the U.S. Sections of the Combustion Institute, pp. 461-464, Washington, D.C., March 14-17, 1999, The Combustion Institute, Pittsburgh.

Chen, S.J. and Dahm, W.J.A. (2000) Experimental results on the coupling between fluid dynamics and combustion in a laminar vortex ring. AIAA Paper No. 2000-4333, 38th AIAA Aerospace Sciences Meeting, January 10 - 13, 2000 , Reno , NV .

Chen, S.-J. and Dahm, W.J.A. (2000) Results from numerical simulation of the diffusion flame-vortex ring interaction. AIAA Paper No. 2000-2468, AIAA Fluids 2000 Fluid Dynamics Meeting, June, 2000, Boulder, CO.

Micro Internal Combustion Swing Engine (MICSE) for Portable Power Generation Systems

This project is developing palm-sized portable power generation systems based on the micro internal combustion swing engine (MICSE). A swing engine is a rotationally oscillating free-piston engine in which combustion occurs in four chambers separated by a single rotating swing-arm in a single base structure. The resulting efficient use of both chamber space and system mass permits lower weight and smaller size at the same power than linear free-piston engines. Successful development of such integrated microengines and generators requires careful consideration of key flow and combustion issues.

Dahm, W.J.A., Ni, J., Mayor, R., Qiao, G., Dyer, S., Benjaminm, A., Gu, Y., Lei, Y., Papke, M. and Mijit, K. (2002) Micro internal combustion swing engine (MICSE) for portable power generation systems. AIAA Paper No. 2002-0722, 40th AIAA Aerospace Sciences Meeting, January, 2002, Reno , NV .

Planar Laser Induced Fluorescence (PLIF) Measurements of Combustion Processes in Turbulent Flames

Planar laser induced fluorescence (PLIF) provides experimental access to key mixing and combustion chemistry information in turbulent flames for use in developing models of turbulent reacting flows. Studies of turbulent combustion processes conducted with various PLIF techniques, including planar CH and OH imaging as well as PIV, have provided key insights for improved understanding of the interaction between the underlying turbulent flow processes and the progress of highly exothermic chemical reactions occurring within them.

Everest, D., Driscoll, J.F., Dahm, W.J.A. and Feikema, D. (1995) Images of the 2D temperature field and temperature gradients to quantify thermal mixing rates within a non-premixed turbulent jet flame. Combustion and Flame, Vol. 101, pp. 58 - 68.

Mullin, J.A., Dahm, W.J.A. and Donbar, J.M. (2000) Combined PLIF and PIV laser imaging measurements of heat release effects at the small scales of turbulent reacting flows. Proc. 10th International Symposium on Application of Laser Techniques to Fluid Mechanics, July 10-13, 2000 , Lisbon , Portugal .

Ratner, A., Driscoll J.F., Donbar, J.M., Carter, C.D., Mullin, J.A. and Dahm, W.J.A. (1999) The new regime of intensely wrinkled and shredded nonpremixed flames - Images of the reaction zone; Proc. Eastern States Section Meeting of the Combustion Institute, Raleigh-Durham, N.C., October 11-13, 1999, The Combustion Institute, Pittsburgh.

Donbar, J.M., Carter, C.D., Ratner, A., Driscoll, J.F. and Dahm, W.J.A. (1998) Simultaneous velocity-scalar measurements within intensely wrinkled nonpremixed flames. Proc. Western States Section Meeting of the Combustion Institute, Paper 98F-37, Seattle, WA October 26-27, 1998; The Combustion Institute, Pittsburgh.

Ratner, A., Donbar, J.M., Carter, C.D., Driscoll J.F. and Dahm, W.J.A. (1999) The regime of intensely wrinkled nonpremixed flames - Images of the CH-OH reaction zones and velocity fields. Proc. 1999 Joint Technical Meeting of the U.S. Sections of the Combustion Institute, Washington, D.C., March 14-17, 1999, The Combustion Institute, Pittsburgh.

Everest, D., Driscoll, J.F., Dahm, W.J.A. and Feikema, D. (1993) Images of the 2D temperature field and temperature gradients to quantify thermal mixing rates within a non-premixed turbulent jet flame. 1993 Fall Meeting of the Eastern States Section of the Combustion Institute, October 25, 1993.

Scalar Imaging Velocimetry (SIV) for Measurements of Velocity Gradient Fields in Turbulent Flows

In this project, a new method was developed and applied to yield the first fully-resolved, non-intrusive, indirect experimental measurements of the spatio-temporal structure and dynamics of the full nine-component velocity gradient tensor field in turbulent flows from conserved scalar imaging measurements. This is based on a variational method in which weighted residuals of the conserved scalar transport equation, the continuity condition, and a derivative smoothness condition are minimized over the space of velocity fields. The technique was validated using DNS for turbulent mixing of a passive scalar, and then applied to fully resolved four-dimensional scalar field measurements from a laboratory turbulent flow. Results provided the space- and time-varying vector vorticity field, the tensor strain rate field, the kinetic energy density field, the kinetic energy dissipation rate field, and the enstrophy field throughout a three-dimensional measurement volume.

Dahm, W.J.A., Su, L.K. and Southerland, K.B. (1992) A scalar imaging velocimetry technique for four-dimensional velocity field measurements in turbulent flows. Physics of Fluids A, Vol. 4, pp. 2191 - 2206.

Su, L.K. and Dahm, W.J.A. (1996) Scalar imaging velocimetry measurements of the velocity gradient tensor field at the dissipative scales of turbulent flows. Part I: Validation tests. Physics of Fluids Vol. 8, No. 7, pp. 1869 - 1882.

Su, L.K. and Dahm, W.J.A. (1996) Scalar imaging velocimetry measurements of the velocity gradient tensor field at the dissipative scales of turbulent flows. Part II: Experimental results. Physics of Fluids Vol. 8, No. 7, pp. 1883 - 1906.

Dahm, W.J.A., Su. L.K. and Southerland, K.B. (1992) Scalar imaging velocimetry measurements of vector velocity, vorticity and tensor strain rate fields in turbulent flows. Proceedings of the 6th International Symposium on Applications of Lasers in Fluid Mechanics, pp. 3.1.1-3.3.6, Instituto Superio Técnico, Lisbon, Portugal.

Su, L.K. and Dahm, W.J.A. (1993) Scalar imaging velocimetry study of the dissipative scales of motion in turbulent flows. AIAA Paper No. 94-0403, 32nd AIAA Aerospace Sciences Mtg, January 10-14, 1994, Reno, NV.

Dahm, W.J.A, Su, L.K. and Tacina, K. (1996) Four-dimensional measurements of vector fields in turbulent flows. AIAA Paper No. 96-1987 (Invited), AIAA Fluid Dynamics Conference, June 18-20, 1996, New Orleans, LA, AIAA, Washington, D.C.

Strained Diffusion and Reaction Layer (SDRL) Model for Nonequilibrium Mixing-Chemistry Coupling in Turbulent Reacting Flows

This project developed an improved type of flamelet model based directly on the fundamentally layer-like fine structure of scalar dissipation rate fields in turbulent reacting flows. Unlike the classical flamelet model, this strained dissipation and reaction layer (SDRL) model does not require thin reaction zones, and can produce broad (distributed) concentration fields and reaction zones, as well as thin (flamelet-like) species concentration and reaction rate fields, depending on the local stoichiometry and the degree of chemical nonequilibrium. The resulting predictions of OH concentrations in a lifted H2-air turbulent jet diffusion flame show significant improvements over the classical flamelet model and relatively good agreement with measured values.

Dahm, W.J.A. and Bish (1993) High resolution measurements of molecular transport and reaction processes in turbulent combustion. Turbulence and Molecular Processes in Combustion, pp. 287 - 302, (T. Takeno, Ed.) Elsevier Science Publ. B.V.

Bish, E.S. and Dahm, W.J.A. (1995) Strained dissipation and reaction layer analyses of nonequilibrium chemistry in turbulent reacting flows. Combustion and Flame, Vol. 100, pp. 457 - 464.

Dahm, W.J.A. and Bish, E.S. (1992) High resolution measurements of molecular transport and reaction processes in turbulent combustion. Invited Paper, Proceedings of the 6th Toyota Conference: Turbulence and Molecular Processes in Combustion, Toyota Research Laboratories, Nagoya , Japan .

Bish, E.S., Dahm, W.J.A. and Dowling, D.R. (1993) A strained dissipation and reaction layer formulation for turbulent diffusion flames. Paper No. 93-063, Proceedings of the 1993 Fall Meeting of the Western States Section of the Combustion Institute, October 18-19, 1993, Menlo Park, CA.

Bish, E.S. and Dahm, W.J.A. (1993) Non-equilibrium structure of H2-air combustion in turbulent jets. AIAA Paper No. 94-0100, 32nd AIAA Aerospace Sciences Mtg, January 10-14, 1994, Reno, NV.

Dahm, W.J.A. and Bish, E.S. (1995) Molecular mixing and chemical reactions in turbulent flows. Proceedings of the Fall 1995 Technical Meeting of the Eastern States Section Meeting of the Combustion Institute, pp. 27-36, The Combustion Institute, Pittsburg.

Bish, E.S. and Dahm, W.J.A. (1995) A validation study of the strained dissipation and reaction layer formulation using direct numerical simulations of a turbulent reacting flow. AIAA Paper No. 95-0803, 33nd AIAA Aerospace Sciences Mtg, January 9-12, 1995, Reno, NV.

Bish, E.S. and Dahm,W.J.A. (1995) A DNS assessment of turbulence-chemistry coupling models for nonpremixed turbulent combustion. Proceedings of the Tenth Symposium on Turbulent Shear Flows, pp. 22.13 - 22.19, Penn State University, University Park, PA.

Fully-Resolved Four-Dimensional Spatio-Temporal Imaging of Conserved Scalar Mixing in Turbulent Flows

This project developed and applied new experimental methods to obtain the first fully-resolved, three- and four-dimensional, spatio-temporal measurements of scalar gradient vector fields in turbulent flows. Each three-dimensional spatial data volume is composed of up to 256^3 spatial data points, with volumes acquired sequentially in time. The four-dimensional data sets are each comprised of over 3 billion individual point measurements, and are simultaneously differentiable in x, y, z, and t, allowing access to the spatial structure and temporal dynamics in these fields. The results provided previously inaccessible insights into the physical structure and statistics of the fine scale structure of scalar mixing in turbulent flows.

Dahm, W.J.A., Southerland, K.B. and Buch, K.A. (1991) Direct, high resolution, four-dimensional measurements of the fine scale structure of Sc » 1 molecular mixing in turbulent flows. Physics of Fluids A, Vol. 3, pp. 1115 - 1127.

Dahm, W.J.A., Southerland, K.B. and Buch, K.A. (1991) Four-dimensional laser induced fluorescence measurements of conserved scalar mixing in turbulent flows. Applications of Laser Techniques to Fluid Mechanics, pp. 3 - 18, (R. Adrian, Ed.) Springer Verlag.

Dahm, W.J.A. and Southerland, K.B. (1992) Quantitative, four-dimensional, laser induced fluorescence imaging studies of scalar mixing in turbulent flows. Flow Visualization 6, pp. 243 - 247, (Y. Tanida & H. Miyashiro, Eds.) Springer-Verlag.

Southerland, K.B., Frederiksen, R.D, Dahm, W.J.A. and Dowling, D.R. (1995) Comparisons of mixing in chaotic and turbulent flows. Chaos Applied to Fluid Mixing, pp. 313 - 345, (H. Aref & M.S. El Naschie, Eds.) Pergamon Press.

Southerland, K.B., Frederiksen, R.D., Dahm, W.J.A. and Dowling, D.R. (1994) Comparisons of mixing in chaotic and turbulent flows. Chaos, Solitons & Fractals, Vol. 4, No. 6, pp. 1057 - 1089.

Dahm, W.J.A. and Southerland, K.B. (1997) Experimental assessment of Taylor's Hypothesis and its applicability to dissipation estimates in turbulent flows. Physics of Fluids Vol. 9, pp. 2101 - 2107.

Dahm, W.J.A. and Southerland, K.B. (1999) Quantitative flow visualization via fully-resolved four-dimensional spatio-temporal imaging. Chapter 11 in Flow Visualization: Techniques and Examples, (A. Smits and T.T. Lim, Eds.), 231 - 258, Imperial College Press, London.

Dahm, W.J.A., Southerland, K.B. and Buch, K.A. (1990) Four-dimensional laser induced fluorescence measurements of conserved scalar mixing in turbulent flows. Proceedings of the 5th International Symposium on Applications of Laser Techniques to Fluid Mechanics, pp. 1.1.1 - 1.1.6, Instituto Superior Técnico, Lisbon, Portugal.

Dahm, W.J.A. and Southerland, K.B. (1992) Quantitative four-dimensional laser induced fluorescence imaging studies of scalar mixing in turbulent flows. 6th International Symposium on Flow Visualization, Yokohama, Japan.

Southerland, K.B. and Dahm, W.J.A. (1993) Four-dimensional laser induced fluorescence study of the structure of molecular mixing in turbulent flows. AIAA Paper No. 94-0820, 32nd AIAA Aerospace Sciences Mtg, January 10-14, 1994, Reno, NV.

Southerland, K.B. and Dahm, W.J.A. (1995) Experimental assessment of Taylor's hypothesis and its applicability to dissipation estimates in turbulent flows. Proceedings of the Tenth Symposium on Turbulent Shear Flows, pp. 1.13 - 1.19, Penn State University, University Park, PA.

Southerland, K.B., Dahm, W.J.A. and Dowling, D.R. (1995) Experimental results fo the high wavenumber spectral structure of scalar mixing in turbulent shear flows. Proceedings of the Tenth Symposium on Turbulent Shear Flows, pp. 28.1 - 28.6, Penn State University, University Park, PA.

Experimental Study of the Fine-Scale Structure of Conserved Scalar Mixing in Turbulent Flows

This study was based on highly resolved, two- and three-dimensional, spatio-temporal, imaging measurements of dynamically passive conserved scalar fields on the inner scales of turbulent shear flows. The resolution and signal quality were sufficient to allow direct differentiation of the measured scalar field to give the instantaneous scalar energy dissipation rate field. Results showed that the fine scale structure of the scalar dissipation field consists entirely of thin, strained, laminar, sheet-like diffusion layers. The internal structure of these dissipation layers agrees well with a one-dimensional self-similar solution for the local strain-diffusion competition in the presence of a spatially uniform but time-varying strain field. Statistics of the scalar field demonstrate similarity with inner scale variables over the range of Reynolds numbers investigated.

Buch, K.A. and Dahm, W.J.A. (1996) Experimental study of the fine-scale structure of conserved scalar mixing in turbulent flows. Part 1. Sc » 1. Journal of Fluid Mechanics, Vol. 317, pp. 21 - 71.

Buch, K.A. and Dahm, W.J.A. (1998) Experimental study of the fine-scale structure of conserved scalar mixing in turbulent flows. Part 2. Sc = 1. Journal of Fluid Mechanics, Vol. 364, pp. 1 - 29.

Dahm, W.J.A. and Buch, K.A. (1989) Lognormality of the scalar dissipation pdf in turbulent flows. Physics of Fluids A, Vol. 1, No. 7, pp. 1290 - 1293.

Dahm, W.J.A. (1998) Fine structure characteristics of large Schmidt number molecular mixing in turbulent flows. Physical Processes and Chemical Reactions in Turbulent Liquids, pp. 39 - 56, (F.R. Rys & A. Gyr, Eds.), A.A. Balkema Pub.

Buch, K.A., Dahm, W.J.A., Dibble, R.W. and Barlow, R.S. (1992) Equilibrium structure of reaction rate fields in turbulent diffusion flames. Proceedings of the Combustion Institute, Vol. 24, pp. 295 - 301.

Dahm, W.J.A. and Buch, K.A. (1991) High resolution, three-dimensional (2563), spatio-temporal measurements of the conserved scalar field in turbulent shear flows. Turbulent Shear Flows 7, pp. 17 - 26, (W.C. Reynolds, Ed.) Springer Verlag.

Dahm, W.J.A. and Buch, K.A. (1989) High resolution, three-dimensional (2563), spatio-temporal measurements of the conserved scalar field in turbulent shear flows. Proceedings of the 7th Symposium on Turbulent Shear Flows, Vol. 1, pp. 14.1.1 - 14.1.6, Stanford , CA .

Dahm, W.J.A., Buch, K.A., Dibble, R.W., Fourguette, D.C. and Barlow, R.S. (1990) Fully resolved instantaneous laser Rayleigh imaging measurements of conserved scalar mixing in lifted turbulent diffusion flames. Poster Paper No. P212, Twenty-third (International) Symposium on Combustion,The Combustion Institute, Pittsburgh , PA.

Dahm, W.J.A. (1992) Experimental studies of the fine scale structure of mixing in turbulent flows. Invited Paper, Proceedings of the Thirteenth Symposium on Turbulence, University of Missouri-Rolla , Rolla , MO.

Scaling of NOx Emissions from Turbulent Combustion in Burners and Furnaces

In this study, data were obtained from a set of five burner scales to provide the first comprehensive NOx and CO scaling data for natural gas burners over the range of thermal loadings from 30 kW to 12 MW. Five identical versions of a generic, swirl-stabilized, natural gas burner were tested in geometrically and thermally similar furnaces. Additional measurements at different geometric and thermal conditions allowed confinement and heat transfer effects on burner scaling to be assessed. Results allowed identification of key sources of NOx production in such flames, and the scaling laws for these sources provided a comprehensive NOx scaling model across the entire range of burner scales considered.

Hsieh, A., Dahm, W.J.A. and Driscoll, J.F. (1996) Scaling laws for NOx emissions performance of burners and furnaces from 30 kW to 12 MW. Combustion and Flame Vol. 114, pp. 54 - 80.

Dahm, W.J.A., Driscoll, J.F., Weber, R., Kezerle, J.A. and Serauskas, R.V. (1995) Scaling characteristics of aerodynamics and NOx emissions in natural gas burners from, 30 kW to 12 MW. Proceedings of the 1996 International Gas Research Conference (IGRC96), November 6-9, Cannes , France .

Hsieh, A., Dahm, W.J.A. and Driscoll, J.F. (1996) Scaling laws for NOx emissions performance of burners and furnaces from 30 kW to 12 MW. Proceedings of the 1996 AFRC International Symposium, American Flame Research Committee (AFRC), September 30 - October 2, 1996 , Baltimore , MD.

Hsieh, A., Dahm, W.J.A. and Driscoll, J.F. (1996) Fundamental scaling of NOx emissions from burners and furnaces. Proceedings of the 1997 Technical Meeting of the Central States Section of the Combustion Institute, Mobile, AL, The Combustion Institute, Pittsburgh.

A Local Integral Method (LIM) for Lagrangian Front-Tracking Simulations of Turbulent Flow, Mixing, and Chemical Reactions

This project developed an LES model for turbulent flow, mixing, and combustion processes. LIM uses the self-similar structure at the diffusive scales of turbulent flows to locally parabolize the governing transport equations around a time-evolving computational surface on which velocity gradients and scalar gradients are concentrated. This transforms the original partial differential equations to a set of ordinary differential equations that can be solved on a time-evolving surface. Information is stored and updated only on this time-evolving surface, rather than on a fixed grid throughout the domain. The LIM equations solved on this surface give the evolution of local gradient profiles around the surface in terms of their local integral moments; the solution can then be reconstructed at any time from the integral moments on this surface.

Tryggvason, G. and Dahm, W.J.A. (1990) An integral method for mixing, chemical reactions, and extinction in unsteady strained diffusion layers. Combustion and Flame, Vol. 83, pp. 207 - 220.

Tryggvason, G., Dahm, W.J.A. and Sbeih, K. (1990) Fine structure of vortex sheet rollup by viscous and inviscid simulation. ASME of Journal of Fluids Engineering, Vol. 113, pp. 31 - 36.

Chang, C.H.H., Dahm, W.J.A. and Tryggvason, G. (1991) Lagrangian model simulations of molecular mixing, including finite rate chemical reactions, in a temporally developing shear layer. Physics of Fluids A, Vol. 3, pp. 1300 - 1311.

Dahm, W.J.A., Tryggvason, G. and Zhuang, M.M. (1995) Integral method solution of time-dependent strained diffusion-reaction equations with multi-step kinetics. SIAM Journal on Applied Mathematics, Vol. 56, No. 4, pp. 1039 - 1059.

Dahm, W.J.A., Tryggvason, G., Frederiksen, R.D. and Stock, M.J. (2000) Local integral moment (LIM) simulations. Chapter 5 in Computational Fluid Dynamics in Industrial Combustion, pp. 161 - 208, (C.M. Baukal, Ed.), CRC Press.

Chang, C.H.H., Dahm, W.J.A. and Tryggvason, G. (1990) A Lagrangian model for simulating combustion, including finite rate chemistry, in complex flows. Poster Paper No. P229, Twenty-third (International) Symposium on Combustion, The Combustion Institute, Pittsburgh , PA.

Suresh, N.C., Dahm, W.J.A. and Tryggvason, G. (1993) LIM computations of chemical reactions in spatially and temporally developing shear flows. AIAA Paper No. 94-0870, 32nd AIAA Aerospace Sciences Mtg, January 10-14, 1994, Reno, NV.

Dahm, W.J.A., Tryggvason, G., Kezerle, J.A. and Serauskas, R.V. (1995) Simulation of turbulent flow and complex chemistry in natural gas combustion processes by local integral moment (LIM) modeling. 1996 International Gas Research Conference (IGRC), November 6-9, Cannes , France .

Suresh , N.C. , Dahm, W.J.A. and Tryggvason, G. (1996) LIM simulations of mixing and chemical reaction in gas reburning applications. Proceedings of the 1996 AFRC International Symposium, American Flame Research Committee (AFRC), September 30 - October 2, 1996 , Baltimore , MD.

Frederiksen, R.D., Dahm, W.J.A., Pratapas, J.M., Serauskas, R.V and Bartok, W. (1997) LIM simulations of gas injection and reburning in two utility boilers. Proceedings of the 1997 AFRC International Symposium, American Flame Research Committee (AFRC), Chicago , IL .

Frederiksen, R.D., Dahm, W.J.A., Pratapas, J.M., Serauskas, R.V and Bartok, W. (1998) Advanced simulation of fuel-lean gas reburning for utility boiler NOx control. Proceedings of the 1998 International Gas Research Conference (IGRC 98), International Gas Research Committee, San Diego , CA .

Experiments and Analysis of Blowout Instability of Turbulent Diffusion Flames

Experimental and theoretical results were obtained for the blowout limits of turbulent jet diffusion flames issuing from sources with arbitrary geometries and exit conditions. Blowout of lifted flames is taken to occur when the entrainment and mixing time scale at the stabilization location decreases below a chemical time scale. Experimental results over a wide range of turbulent jet diffusion flames showed excellent agreement with with the resulting predictions, including the effect of the far-field equivalent source diameter for complex source geometries.

Dahm, W.J.A. and Dibble, R.W. (1988) Coflowing turbulent jet diffusion flame blowout. Proceedings of the Combustion Institute, Vol. 22, pp. 801 - 808.

Dahm, W.J.A. and Mayman, A.G. (1990) Blowout limits of turbulent jet diffusion flames with arbitrary source conditions. AIAA Journal, Vol. 28, No. 7, pp. 1157 - 1162.

Dahm, W.J.A. and Dibble, R.W. (1988) Combustion stability limits of coflowing turbulent jet diffusion flames. AIAA Paper No. 88-0538, AIAA, Washington, D.C.

Experiments on Vortex Ring Mixing and Interaction with Density Interfaces

This project conducted experiments revealing the dynamics of vortex ring interaction with a density interface. Similarity considerations for both thin and thick density interfaces indicate that the interaction is governed by just two dimensionless parameters, and in the Boussinesque limit reduces to the product of these two parameters. Details of the interaction dynamics were experimentally documented over a range of parameter values, and confirmed the similarity scalings for both thin and thick interfaces. Numerical simulations extended the results to large density differences.

Dahm, W.J.A., Scheil, C.M. and Tryggvason, G. (1989) Dynamics of vortex interaction with a density interface. Journal of Fluid Mechanics, Vol. 205, pp. 1 - 43.

Southerland, K.B., Porter, J.R., Dahm, W.J.A. and Buch, K.A. (1991) An experimental study of the molecular mixing process in an axisymmetric laminar vortex ring. Physics of Fluids A, Vol. 3, pp. 1385 - 1392.

Southerland, K.B., Porter, J.R., Dahm, W.J.A. and Buch, K.A. (1990) An experimental study of the molecular mixing process in an axisymmetric laminar vortex ring. Poster Paper No. PD-9, IUTAM Symposium on Fluid Mechanics of Stirring and Mixing, UC San Diego, La Jolla, CA.