Dimitri Papamoschou
Professor, Mechanical & Aerospace Engineering
The Henry Samueli School of Engineering
The Henry Samueli School of Engineering
PH.D., California Institute of Technology
OTH, B.S., Syracuse University
OTH, B.S., Syracuse University
University of California, Irvine
Room 4214 Engineering Gateway
Mail Code: 3975
Irvine, CA 92697
Room 4214 Engineering Gateway
Mail Code: 3975
Irvine, CA 92697
Research Interests
Compressible turbulence, jet-noise reduction, respitatory flows, laser diagnostics.
Websites
Academic Distinctions
Appointments
Research Abstract
Mach wave elimination in supersonic jets: A novel technique has been developed which eliminates Mach waves from supersonic jets. Suppression of Mach-wave noise is a key challenge to the development of future supersonic transports such as the HSCT. The present method relies on propulsive means to eliminate Mach waves. This is in contrast to conventional methods like lobe mixers that confine the extent of--not eliminate--Mach waves with appreciable thrust and performance penalties. Two patents have issued.
Evolution and morphology of large-scale turbulent structures in supersonic shear layers: Planar Laser-Induced Fluorescence (PLIF), in a double-exposure arrangement, is applied in a new supersonic facility to examine the role of large-scale structures in shear layer mixing at high Mach numbers. The research is motivated by the advent of scramjets (supersonic combustion ramjets) and is also relevant to supersonic jet noise. Structure geometry, propagation, and evolution are examined. The convective velocity Uc of the structures is measured by applying 2D cross-correlation schemes to the digital images. The experiments reveal the existence of fast and slow modes of Uc. This directly impacts supersonic jet noise and may have profound influence on entrainment, mixing and combustion at high Mach numbers.
Measurement of power spectra in compressible turbulence: A new optical method that measures directly the three-dimensional power spectrum of refractive-index fluctuations in compressible turbulence is applied to supersonic shear layers. Experiments take place in a new supersonic facility at UCI. The resulting spectra are in accordance with predictions of prevailing theories on isotropic and anisotropic turbulence. Knowledge of spectrum behavior at high wavenumbers is essential for sub-grid modeling in Large-Eddy Simulations. The results are also pertinent to light transmission through aerodynamic windows.
Hindrance of communication in supersonic shear flows: The root cause of poor mixing at supersonic velocities appears to be hindrance of communication between regions of the flow field caused by the Mach number. This phenomenon is being investigated by means of geometric acoustics and by Direct Numerical Simulations in cooperation with Stanford University/NASA Ames. Results show a precipitous decline in communication as Mach number increases, with resulting suppression of turbulence fluctuations.
Entropy generation due to supersonic mixing: Entropy rise due to mixing at supersonic speeds can create substantial loss in total pressure, with adverse implications in ability to generate thrust. Theoretical investigations of parallel-mixing configurations reveal serious losses in thrust as the convective Mach number exceeds unity. It is desired to complement the theoretical studies with experiments in the UCI Supersonic Turbulence Laboratory.
Heliox respiration: effect on oxygen transport through narrowed airways: We are investigating the respiratory flow of heliox (helium-oxygen mixtures) through models of obstructed airways. Large and small airways have been studied. In both cases, heliox provides a significant benefit in the pressure-flow relations versus similar nitrogen-oxygen mixtures. For example, for 80%-20% heliox, the maximum pressure needed to drive a given flow rate is about 50% less than that for 80%-20% nitrox.
Evolution and morphology of large-scale turbulent structures in supersonic shear layers: Planar Laser-Induced Fluorescence (PLIF), in a double-exposure arrangement, is applied in a new supersonic facility to examine the role of large-scale structures in shear layer mixing at high Mach numbers. The research is motivated by the advent of scramjets (supersonic combustion ramjets) and is also relevant to supersonic jet noise. Structure geometry, propagation, and evolution are examined. The convective velocity Uc of the structures is measured by applying 2D cross-correlation schemes to the digital images. The experiments reveal the existence of fast and slow modes of Uc. This directly impacts supersonic jet noise and may have profound influence on entrainment, mixing and combustion at high Mach numbers.
Measurement of power spectra in compressible turbulence: A new optical method that measures directly the three-dimensional power spectrum of refractive-index fluctuations in compressible turbulence is applied to supersonic shear layers. Experiments take place in a new supersonic facility at UCI. The resulting spectra are in accordance with predictions of prevailing theories on isotropic and anisotropic turbulence. Knowledge of spectrum behavior at high wavenumbers is essential for sub-grid modeling in Large-Eddy Simulations. The results are also pertinent to light transmission through aerodynamic windows.
Hindrance of communication in supersonic shear flows: The root cause of poor mixing at supersonic velocities appears to be hindrance of communication between regions of the flow field caused by the Mach number. This phenomenon is being investigated by means of geometric acoustics and by Direct Numerical Simulations in cooperation with Stanford University/NASA Ames. Results show a precipitous decline in communication as Mach number increases, with resulting suppression of turbulence fluctuations.
Entropy generation due to supersonic mixing: Entropy rise due to mixing at supersonic speeds can create substantial loss in total pressure, with adverse implications in ability to generate thrust. Theoretical investigations of parallel-mixing configurations reveal serious losses in thrust as the convective Mach number exceeds unity. It is desired to complement the theoretical studies with experiments in the UCI Supersonic Turbulence Laboratory.
Heliox respiration: effect on oxygen transport through narrowed airways: We are investigating the respiratory flow of heliox (helium-oxygen mixtures) through models of obstructed airways. Large and small airways have been studied. In both cases, heliox provides a significant benefit in the pressure-flow relations versus similar nitrogen-oxygen mixtures. For example, for 80%-20% heliox, the maximum pressure needed to drive a given flow rate is about 50% less than that for 80%-20% nitrox.
Available Technologies
Publications
Debiasi, M., and Papamoschou, D. "Noise from Imprefectly Expanded Supersonic Coaxial Jets," AIAA Journal, Vol. 39, No.3, 2001, pp. 388-395.
Papamoschou, D., and Debiasi M., "Directional Suppression of Noise from a High-Speed Jet" AIAA Journal, Vol. 39, No.3, 2001, pp. 380-387.
Murakami, E., and Papamoschou, D., " Eddy Convection in Supersonic Coaxial Jets," AIAA Journal, Vol. 38, No.4, 2000, pp. 628-635.
Dahl, M.D., and Papamoschou, D., "Supersonic Coaxial Jets:
Noise Predictions and Measurements," AIAA Journal, Vol. 38, No.4, 2000, pp. 584-591.
Noise Predictions and Measurements," AIAA Journal, Vol. 38, No.4, 2000, pp. 584-591.
Papamoschou, D., and Debiasi, M., "Noise Measurements in Supersonic Jets Treated with the Mach Wave Elimination Method," AIAA Journal, Vol. 37, No.2, 1999, pp. 154-160.
Link to this profile
https://faculty.uci.edu/profile/?facultyId=2077
https://faculty.uci.edu/profile/?facultyId=2077
Last updated
03/05/2002
03/05/2002