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FPCE Research

Research in the Flow Physics and Computational Engineering Group incorporates a multi-disciplinary approach to solving problems at a fundamental level. We have built an ambitious team with a broad range of expertise in topics such as computational fluid dynamics, adaptive methods, physics-based meshing, numerical analysis, multiphase flow, neutronics, and scientific visualization. By closely coupling these diverse capabilities, we are able to tackle complex, real-world problems in a wide range of engineering and scientific application areas. Here are a few examples:

Experimental Support for UQ, Eaton's experiments

Multiphysics Simulation

Multiscale Methods

Scientific Computing

Validation and Verification

Hypersonic Flow and Acoustics

As a part of the Predictive Science Academic Alliance Program (PSAAP), many FPCE faculty and student are working to predict the performance of hypersonic air-breathing vehicles using computational methods with unprecedented accuracy and quantifiable measures of variability. By focusing on off-design conditions to identify and characterize the operability limits of the propulsion system and, specifically, the failure modes associated with engine unstart, we are working to build a "mixed fidelity" and multidisciplinary computational infrastructure of this complex and highly integrated engineering system.

Air-breathing scramjet multiphysics schematic
Air-breathing scramjets involve strongly coupled multiscale multiphysics. Stanford researchers are building verified and validated computational simulations to predict the properties and dynamics of these complex systems.

Shock-Turbulence Interactions

Compressible multiphase flow is an area of emergent practical interest, particularly for the analysis of explosions and energetic dispersal of fluid and solid materials. In order to develop models for such complex physics phenomena, and collaborators have performed direct numerical simulations of such flows and accurately captured the dynamics of high-impedance interfaces and evolving topology. The shock-induced collapse of a cylindrical helium bubble in air and subsequent density variation is shown below.

3D Shock/Turbulence Interaction Mach 1.22 in air impacting a helium bubble
3D Shock/Turbulence Mach 1.22 shock in air impacting a helium bubble

Experimental Support for Uncertainty Quantification

Shock/boundary layer interactions play a critical role in many engineering systems including scramjets. To assess the accuracy of computational turbulence closure models for such complex systems, a group of computational scientists and experimenters have been working side-by-side to build a robust experimental setup of a fully three-dimensional shock/boundary layer interaction in a low-aspect ratio geometry (shown below). Small actuator flaps protruding into the test channel exit flow are used to collect data on the effects of small, deterministic perturbation in the flow to assess the sensitivity of the computational models to imperfect boundary condition specifications, e.g. perturbations in the back pressure should produce significant changes in the shock shape and affect the boundary layer. The goal of this research is to measure the sensitivity of shock-boundary layer interactions to upstream surface roughness and test the capability of codes to predict the sensitivity to these geometric perturbations

Experimental Support for Uncertainty Quantification
Shock/boundary layer interaction experiment in a fully three-dimensional geometry with a low aspect ratio and the flaps used to perturb the inlet/boundary conditions for comparison with simulation data.

DNA Dynamics and Gene Sequencing

Understanding the detailed dynamics of single macromolecules, such as DNA, is essential to the practical development and ultimate utility of microdevices. Professor Eric Shaqfeh's research group focuses on how such long chain polymers behave when confined to geometries of the same size as the molecules themselves: the precise situation arising in microfluidic devices.

Currently there is demand for improved techniques to separate genomic DNA. New separation methods for gel and capillary electrophoresis are being explored using theory, computation and experiments in precisely machined arrays of posts to serve as a DNA sieving medium. By using these post fields to stretch DNA and thereby expose the genetic information, Professor Shaqfeh is able to probe for the presence of specific genetic sequences. These dynamics are vastly different than those in large macroscopic flows, and a precise knowledge of how the chains behave is imperative in a variety of fields, including the modeling of the macroscopic rheology of polymer solutions and single chain microfluidic manipulation.

DNA Polymer Dynamics and Gene Sequencing
Microfluidic sieving employs a series of silicon pins and posts to force DNA strands to flow through the microfluidic array so that the DNA is sequenced and separated (left). The conformation space of a DNA molecule tethered to a surface is being explored to stretch the DNA for ultimate placement as a molecular wire (right).

Bio-Molecular Modeling and Microfluidics

Strong hydrodynamic and electrostatic interactions with nearby particles or walls strongly affect the sedimentation of such systems as well as the configurational dynamics of elongated microparticles (figure on the right below). Professor Eric Darve's research group is developing novel numerical algorithms to probe the properties of bio-molecules at the nano-scale (figures below on the left and in the center). For example, Darve has created techniques to make predictions at the relevant bio-chemical timescales (millisecond) while brute force methods are often limited to microseconds.

Bio-Molecular Modeling and Microfluidics
Molecular model of an amphipathic peptide protein inside a membrane used in molecular dynamics simulations (left). Acid-sensing ion channel that controls the flow of ions in touch receptor neurons (center). Sedimentation of charged fibers such as DNA in microfluidic sieving (right).

DNS of a Zero-Pressure Gradient Flat Plate Boundary Layer

One of the most important applications of turbulence theory is the calculation of the drag forces generated by turbulence near walls of hypersonic vehicles, planes, trains, and automobiles, and even along the Earth's surface in the planetary boundary layer. A zero-pressure gradient flat plate boundary layer (ZPGFPBL) is a prime example of such a flow and forms a critical test case for turbulence modeling efforts and engineering design. Professor Wu and Professor Moin have taken a Blasius layer from Reθ = 80 through transition to a turbulent ZPGFPBL in well controlled manner by direct numerical simulation (DNS). A striking preponderance of hairpin vortical motions were discovered shown below. These research efforts increase our understanding of the physics of wall-bounded turbulent flows.

Zero-Pressure Gradient Flat Plate Boundary Layer
Snapshots of laminar, transitional and turbulent flow in a ZPGFPBL.
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Page last modified on April 15, 2013, at 01:42 AM PST