Research

Research Themes

  • Numerical methods for fluid mechanics

    I have been developing immersed boundary (IB) methods to simulate turbulent flows in a Reynolds-Averaged Navier-Stokes context with application complex, industrial problems during my PhD thesis ( more ). This research led to the introduction of novel IB conditions based on turbulent wall-models ( more ) and adaptive grids ( more ). More recently we have explored the use of IB for conjugate heat transfer problems ( more ) and for aero-acoustics applications ( more ). The methods that I developed are routinely used in industry for design studies ( more ). I also wrote a review article ( more ) on IB methods (with Prof. R. Mittal) that is one of the most cited (10th) and downloaded (7th) papers in Annual Review of Fluid Mechanics ( see ).

  • Physical models for laminar/turbulent flows

    The development of models for turbulent flows has been the original theme that attracted me to Stanford. I worked with Prof. P. Durbin on a variety of problems involving the V2F model: heat transfer ( more ), separation ( more ), unsteady effects ( more ). I developed V2F implementations for commercial codes ( more ) that are now used by 100s of engineers worldwide. More recently we have developed an anisotropic eddy diffusion model based on the V2F framework ( more ). We have also studied transition to turbulence in high-speed flows using DNS ( more ), and more recently applying uncertainty quantification techniques ( more ). I have also been involved in a detailed investigation of the effect of non-Newtonian stresses in turbulent and transitional flows. I have developed a Reynolds-averaged model for polymer solutions ( more ) and we have used DNS to study the transition characteristics of the wake of a cylinder in the presence of polymer injection ( more ).

    Uncertainty Quantification in Computational Science

    This is the most recent focus of my research. I have been leading the uncertainty modeling in the DoE PSAAP Center at Stanford. Our focus is on high-speed reactive flows and we have developed new techniques to handle highly non-linear system responses driven by shocks ( more ), problems with large number of uncertainties induced by imprecise reaction rates ( more ), and extended existing techniques to solve genuinely hyperbolic systems ( more ). An important area of research is the assessment of uncertainties induced by assumptions in physical model, for example turbulence ( more ) or mixing. More recently I have been interested in optimization under uncertainty ( more ).

Predictive Science Academic Alliance Program (PSAAP)




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 behind 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


Uncertainty Quantification in Reacting Flows




Uncertainty in the prediction of CO concentration for Sandia Flame D induced by imperfect measerements of the reaction rates.

  • The research in this project is focused on the development of efficient numerical algortihms to characterize the uncertainty induced by imprecise measurements of reaction rates. This is a critical challenge in predictive simulations of reactive flows as most of the algortihms current available either require a very large number of solutions and their cost increases exponentially with the number of uncertain inputs.
  • We are developing methods based on separated representations whose computational cost increases only linearly with the number of uncertainties.

  • The project is sponsored by KAUST


Modeling and simulations of scalar dispersion in urban environments (Completed)




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 has been sponsored by the Army High Performance Computing Research Center


Fluid Mechanics of Formula 1 Tires (Completed)




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 has been sponsored by Toyota Formula 1 Team


Effect of roughness in hypersonic boundary layers (Completed)




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 has been sponsored by NASA