Completed Projects

I. Buoyant Plume and Flame Instabilities and Dynamics

This research is aimed at an in-depth understanding of buoyant plume instabilities in non-reacting plumes (helium and helium/air mixtures) as well as buoyant diffusion flames. The pulsatile instability in the buoyant regime exhibits itself as periodic oscillations of the plume boundaries near the source of a plume, leading to formation of large scale vortical structures which convect through the plume affecting its dynamics and entrainment characteristics. Our experimental research is focused on the identification and correlation of the limits of the oscillatory regime, characterization and correlation of pulsation frequencies and plume behavior under external periodic forcing. Additionally, computational simulations of the unsteady behavior of planar and axisymmetric buoyant plumes are being carried out using the Lagrangian vortex element technique in collaboration with Prof. Marios Soteriou's research group. Some sample images of buoyant non-reacting plumes (unforced planar, unforced axisymmetric, forced axisymmetric) and unforced buoyant axisymmetric diffusion flames are shown

Buoyant Plume Instabilities:

Planar Helium Plume	Axisymmetric Helium Plume	Axisymmetric Helium Plume forced at 5 Hz

Buoyant Flame Instabilities:

Varicose Instability in a Buoyant Propane Flame	Sinuous Instability in a Buoyant Propane Flame	Same Flame Stabilized in a O2/He Atmosphere

Graduate Students: Tarek Ahmed (Ph. D.'95), Kent D. Kasper (M. S. '95), Yan Dong (M.S. '99)

Publications:

Soteriou, M. C., Dong, Y. and Cetegen, B. M., “Lagrangian simulation of the unsteady near field dynamics of planar buoyant plumes”, Physics of Fluids , Vol. 14, No. 9, pp. 3118-3140, 2002

Cetegen, B. M. and Dong, Y., "Experiments on instability modes of buoyant diffusion flames and effects of ambient atmosphere on instabilities", Experiments in Fluids, Vol. 28 (6), pp.546-558, 2000

Cetegen, B. M., "Integral analysis of planar and axisymmetric steady laminar buoyant diffusion flames", Combustion Theory and Modeling, Vol. 3, pp.13-32, 1999

Cetegen, B. M., "A phenomenological model for near-field fire plume entrainment", Fire Safety Journal, Vol. 31, pp. 299 - 312, 1998

Cetegen, B. M., Dong, Y., and Soteriou, M. C., "Experiments on stability and oscillatory behavior of planar buoyant plumes", Physics of Fluids, Vol. 10, No. 7, pp. 1658 - 1665, 1998

Cetegen, B. M., "Behavior of naturally oscillating and periodically forced axisymmetric buoyant plumes of helium and helium-air mixtures", Physics of Fluids, Vol. 9. No. 12 , pp. 3742-3753, 1997

Cetegen, B. M., "Measurements of Instantaneous Velocity Field of a Nonreacting Pulsating Buoyant Plume by Particle Image Velocimetry", Combustion Science and Technology, Vol. 123,:1-6, p. 377, 1997.

Cetegen, B. M. and Kasper, K. D., "Experiments on the Oscillatory Behavior of Buoyant Plumes of Helium and helium/Air Mixtures", Physics of Fluids, Vol. 8 (11), pp. 2974-2984, 1996.

Cetegen, B. M. and Ahmed, T., "Experiments on the Periodic Instability of Buoyant Plumes and Pool Fires", Combustion & Flame,Vol.93, pp.157-184 , 1993

II. Mixing Enhancement in Compressible Flows and Detonation Dynamics

In this research effort, we are investigating the levels of mixing enhancement achievable when non-uniform composition (and density) jets and vortices interact with weak shock waves. Experiments involve planar imaging of Mie and Rayleigh scattering of the laser illuminated flow field downstream of shock interaction. The flow configurations studied so far include: (1) turbulent axisymmetric jet interacting with weak normal shock waves (M_s = 1.1 - 1.5) and (2) compressible vortex pairs colliding head-on with weak normal shock waves. Sample images from each are shown below. Additionally, interactions of multiple detonations are investigated experimentally to device new ways of anchoring oblique detonation waves in supersonic streams.

Shock-jet and Shock-vortex ring Interactions:

Interaction of Periodically Generated Cylindrical Detonations

Framing pictures of successively initiated detonations in a stichiometric mixture of C2H2/O2 at 40 kPa to simulate pulsed initiation of cylindrical (or spherical) detonations in a hypersonic stream at different frequencies: 1.2x105 Hz (left),1.6x105 Hz (center), 2.4x105 Hz (right).

Graduate Students: Daniel Alessandri (M. S.' 93), Barbara Berger (Visiting Researcher CNRS, France, 1995)

Collaborators: Prof. Eli K. Dabora, University of Connecticut, Prof. James C. Hermanson, Worcester Polytechnic Institute

Publications:

Cetegen, B.M., Crary, L.F. and Dabora, E.K., "The interaction of periodically generated cylindrical detonations in a stimulated hypersonic flow", Transactions of the Combustion Institute Vol. 28, 2000

Hermanson, J. C. and Cetegen, B. M., "Interaction of non-homogeneous axisymmetric turbulent jets with weak normal shock waves", Physics of Fluids, Vol. 12 (5) pp.1210-1225, 2000

Hermanson, J. C. and Cetegen, B. M., "Mixing augmentation during interaction of weak shock waves with non-homogeneous turbulent jets", Proceedings of the Twenty-seventh Symposium (International) on Combustion, pp. 2047-2053, The Combustion Institute, (1998)

Cetegen, B. M. and Hermanson, J. C., "Mixing Characteristics of Compressible Vortex Rings Interacting with Normal Shock Waves", Combustion & Flame, Vol 100, pp.232-240, 1995.

Alessandri, D. S. and Cetegen, B. M., "Experiments on mixing enhancement in non-homogeneous axisymmetric jets swept by weak shock waves" Shock Waves @ Marseille IV,Editors: R. Brun and L. Z. Dumitrescu, pp. 331-336 Springer-Verlag, 1995.

III. Particle/Droplet Dispersion in Two-phase Turbulent Shear Flows

This project involves fundamental research into particle and droplet dispersion in two-phase turbulent flows as it relates to a wide range of applications. Our experiments focus on the droplet dispersion in isothermal and differentially-heated turbulent mixing layers. Gas phase and droplet phase are experimentally characterized by hot-wire anemometry, thermocouples and phase Doppler particle anemometry (PDPA). Some flow visualization is also performed by laser Mie-scattering.

Graduate Student: Mohamed Tageldin (Ph. D.' 96)

Publications:

Tageldin, M. S. and Cetegen, B. M., "Development of mixing and dispersion in a droplet-laden, confined mixing layer" Combustion Science & Technology, Vol.130: 1-6, pp. 131 - 169, 1998

Tageldin, M. S. and Cetegen, B. M., "Dispersion and Evaporation of Liquid Droplets in a Differentially-heated Confined Mixing Layer", presented at the 1995 Eastern States Meeting of the Combustion Institute, Worcester Polytechnic Institute, October 15 - 18, 1995

Tageldin, M. S. and Cetegen, B. M., "Size Selective Dispersion of Droplets in an Isothermal Confined Mixing Layer", presented at the 1995 Eastern States Meeting of the Combustion Institute, Worcester Polytechnic Institute, October 15 - 18, 1995

IV. Thermal Spray Processes and Diagnostics

This research concerns definition of processing conditions that are favorable to deposition of nano-structured thermal barrier coatings (TBCs). Nano-structured coatings are speculated to have superior thermal and mechanical properties in comparison to their conventional counterparts. We are currently making measurements of velocity and temperature of particles that are accelerated and heated in a thermal spray (a DC arc plasma or a high velocity oxy-fuel, HVOF delivery system). These measurements along with computational modeling and high speed imaging of the particle impact onto substrates enable to understand the dynamics of deposition and the most favorable deposition conditions for the formation of nano-structure. Currently, a custom-built two color pyrometer is used to measure particle temperatures along with a two component phase Doppler particle anemometer (PDPA) to determine particle velocities and size (if they are smooth and spherical). Additionally, a high speed framing camera (2 x 10⁶frames/sec) is being used to image the particle impact phenomenon. Additionally, spatially resolved emission spectroscopy of Argon-Hydrogen plasmas is performed to measure plasma temperature fields.

Visualization of External Particle Injection into an Argon Plasma Stream:

Graduate Students: Weidou Yu (Ph.D. '99), Sergey Semenov (Ph.D. 2002) and Alper Ozturk (Ph.D. Candidate)

Collaborator: Prof. Theodore Bergman

Publications:

Semenov, S. Y. and Cetegen, B. M., "Spectrocopic temperature measurements in DC-arc plasma jets utilized in thermal spray processing of materials", Journal of Thermal Spray Technology, Vol. 10 (1), March 2001

Cetegen, B. M. and W. Yu, "Simultaneous particle temperature, velocity and size measurements in HVOF Thermal Sprays", Journal of Thermal Spray Technology, Vol. 8 (1), pp. 57 -67, March 1999

Yu, W., Strutt, P. and Cetegen, B. M., "Particle Temperature Measurements by Two-color Pyrometry in Thermal Sprays" Progress Report to Office of Naval Research, Contract #N0014-95-0829, March 1997.

Yu, W, Strutt, P. and Cetegen, B. M. "Particle Temperature Measurements in a HVOF Thermal Spray by Two color Radiant Emission Pyrometry" , 1997 Fall Meeting of the Materials Research Society, December 1- 5, 1997, Boston MA.