Research

Simulations of dispersion scenarios in downtown Chicago. Under the same wind conditions, few hundred feet displacement of the release source can lead to large differences in the downstream dispersion.

• The characterization of hazard dispersion is the focus of the present project. We are specifically interested in the details of the turbulence transport and mixing resulting from the complex topography during the initial cloud formation; in addition the effects of non-Newtonian dynamics and the presence of thermal stratification are being considered
• The description of the geometry is based on the Immersed Boundary method which has been modified to handle topography files in GPS format. Computational grids with anisotropic local grid refinement are automatically generated to capture the desired spatial scales in the vicinity of the release source.
• Computations are performed either using DNS/LES for isolated buildings, and by employing RANS modeling for large scale predictions. One specific focus of the project is the development of an accurate model of the turbulent scalar flux, based on generalized gradient diffusion hypothesis.


• The project is sponsored by the Army High Performance Computing Research Center
• R. Rossi and G. Iaccarino, “Numerical simulation of scalar dispersion downstream of a square obstacle using gradient-transport type models” Atmospheric Environment, Vol. 43, No. 16, pp. 2518-2531, 2009.
• D. Phillips, R. Rossi, G. Iaccarino, “Numerical simulation of scalar dispersion in separated flows using algebraic flux models “, 6th International Symposium on Turbulence, Heat and Mass Transfer, Rome, Italy, September 14-18, 2009.
• G. Iaccarino and R. Rossi, “DNS of scalar dispersion behind a square obstacle,” Army Science Conference, 2008.

Simulations of hypersonic air-breathing propulsion vehicle, the HyShot system. Simulations are based on RANS modeling and include both reacting and non-reacting computations. ness element.

• The overarching goal of this project is to characterize the operability limits of an hypersonic vehicle; in particular we are focusing on the unstart phenomena, a critical failure of air-breathing propulsion systems. The main research is in Uncertainty Quantification; we are using a Bayesian inversion technique to control the unstart process, and a Pade-Legendre reconstruction algorithm to represent the performance of the propulsion system as a function of the uncertainty in the flight conditions.
• The main thurst bedinh the research in uncertainty quantification is the development of new, more efficient algorithms to propagate uncertainty through a computational code, and the introduction of a strategy to characterize modeling uncertainties (in turbulence and combustion models)


• The project is sponsored by US DoE/NNSA
• Iaccarino G., Pecnik R., Glimm J, Sharp D., "A QMU approach for characterizing the operability limits of air-breathing hypersonic vehicles" LANL Report LA-UR 09-01863. (Submitted to Journal Propulsion and Power) 2009.
• Chantrasmi T., Doostan A., Iaccarino G., "Pade-Legendre Approximant for Uncertainty Quantification with Discontinuous Response Surfaces" Journal of Computational Physics, Vol. 228 (19), pp. 7159–7180, 2009.

Simulations of high-speed boundary layer on a flat plate with a discrete roughness element. The picture shows contours of density to identify the edge of the boundary layer and a weak compression shock downstream of the roughness element.

• We are performing numerical simulations of high speed boundary layers on plates characterized by discrete or distributed roughness elements. The objective is to identify the effect of protuberances in the amplification of small perturbations that can eventually lead to turbulence breakdown. Our simulations are based high-order numerical discretization schemes and consider different gas properties to characterize boundary layers on vehicles entering the Earth or Martian atmosphere.
• The description of the geometry is based on the Immersed Boundary method which has been modified to retain the accuracy of the high order discretization used in the solution of the compressible Navier-Stokes equations. We use a forcing method to enforce the boundary conditions.


• The project is sponsored by NASA
• O. Marxen, J. Giegel, and G. Iaccarino, “Transitional and turbulent high-speed boundary-layers on surfaces with distributed roughness,” AIAA-2009-0171.
• O. Marxen, G. Iaccarino, and E.S.G. Shaqfeh, “Numerical simulation of the effect of a roughness element on high-speed boundary-layer instability,” AIAA-2008-4400.

Simulations of the turbulent flow around a realistic Formula 1 tire. The contours show pressure distributions on an horizontal plane close to the ground to illustrate the vortical structures.

• The objective of this research is to study the aerodynamic wake generated by rotating tires and to assess the accuracy of turbulence models used in the simulations. We are performing both numerical simulations and experiments (in collaboration with Prof. J. Eaton) and we are also investigating the effect of uncertainties in the tire deformation of the wake structures
  
• The project was sponsored by Toyota Formula 1 Team
• J. Axerio and G. Iaccarino, “Wake Dynamics of Formula 1 Tires -A Comprehensive Analysis of the Flow Behind a Non-Rotating Wheel Using Numerical Simulations and Experiments,” SAE Paper 09B-0082.