Ramesh Pankajakshan

DOE's Effort to Reduce Truck Aerodynamic Drag Through Joint Experiments and Computations

Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOEs mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.

Parallel solution of viscous incompressible flow on multi-block structured grids using MPI

Publisher Summary The aim of this chapter is to develop a parallel code based on an existing unsteady three-dimensional incompressible viscous flow solver for simulation of flows past complex configurations using multi-block structured grids and using message passing interface (MPI) for message passing. The linearized implicit solution algorithm used is modified for execution in parallel using a block-decoupled sub-iterative strategy, and a heuristic performance estimate is developed to guide the parallel problem definition. The chapter provides extensive evaluations of both algorithmic and parallel performance for a test problem consisting of axisymmetric flow past an unappended submarine hull with a Reynolds number of 12 million. Other results are given for three-dimensional appended submarine cases having 0.6M and 3.3M grid points. The decoupled sub-iteration algorithm allows the convergence rate of the sequential algorithm to be recovered at reasonable cost by using a sufficient number of sub-iterations, and allows decompositions having multiple subdivisions across boundary layers. The chapter concludes that the present approach gives reasonable parallel performance for large scale steady flow simulations wherein the grid and decomposition are appropriately sized for the targeted computer architecture.

Combining Computational Fluid Dynamics and Agent-Based Modeling: a new approach to evacuation planning.

We introduce a novel hybrid of two fields—Computational Fluid Dynamics (CFD) and Agent-Based Modeling (ABM)—as a powerful new technique for urban evacuation planning. CFD is a predominant technique for modeling airborne transport of contaminants, while ABM is a powerful approach for modeling social dynamics in populations of adaptive individuals. The hybrid CFD-ABM method is capable of simulating how large, spatially-distributed populations might respond to a physically realistic contaminant plume. We demonstrate the overall feasibility of CFD-ABM evacuation design, using the case of a hypothetical aerosol release in Los Angeles to explore potential effectiveness of various policy regimes. We conclude by arguing that this new approach can be powerfully applied to arbitrary population centers, offering an unprecedented preparedness and catastrophic event response tool.

Aerodynamic Simulation of Heavy Trucks with Rotating Wheels

Aerodynamic simulations were carried out for the Ground Transportation System model, a 1/8 th scale tractor-trailer model, that was tested in the NASA Ames 7’x10’ tunnel. The computed forces and pressure coefficients are compared to experiment. Detailed comparisons are also carried out for the wake in the symmetry plane of the model. A DES version of the two equation k-e/k-ω ω ω ω hybrid turbulence model is shown to predict the single vortex structure observed in the experiment. Simulations are also carried out for an isolated rotating wheel and the results are compared to experiment data. A theoretically predicted jet arising at the contact patches was observed computationally with its magnitude matching the theoretical predictions. Representative simulations were also carried out for a tractortrailer model with rotating wheels.

Passive Devices for Reducing Base Pressure Drag in Class 8 Trucks

Full scale CFD simulations of the Generic Conventional Model (GCM), a simplified model of a Class 8 truck, were used to explore passive devices for improving the drag performance of the trailer base. Significant improvements over conventional straight base flaps were achieved using an Extended Bent (EB) flap that stays within the length limits imposed by US federal law. An additional boat tail device for the cab bogie base was also found to yield improvements in the base drag in that region. This device in combination with the EB flap leads to a wind-averaged drag reduction of 21 % over the non-modified GCM model. An under-trailer scoop to generate air for pressurizing the trailer base or for use in active flow control devices was found to add too much drag to be effective.

Turbofan flowfield simulation using Euler equations with body forces

A method for flow computations around ducted propfans is presented. The approach is to use the body force terms in the three-dimensional Euler equations to model the propeller. Numerical solutions are compared with experimental data for three ducted propfan configurations for different flow conditions.

Scalable Parallel Implicit Algorithm for Advanced Turbulence Closures

*† ‡ § Two Reynolds Stress models are implemented in an existing scalable parallel incompressible flow solver. Computations for standard channel and flat plate cases are compared to theoretical and Direct Numerical Simulation results. Simulations of the DARPA SUBOFF body are compared to experimental data. The simulations displayed robust convergence for high Reynolds number flows with sublayer resolved grids. Reynolds stress model based simulations were found to be a third more expensive than two-equation turbulence model computations in terms of runtime. Nomenclature Cp = pressure coefficient Cf = skin friction coefficient j iu u ′ ′ − = Cartesian components of the Reynolds stress tensor K = turbulent kinetic energy ( ) k ku u ′ ′ 2 1 k v = mean flow contravariant velocity components m u = mean flow Cartesian velocity components m x = Cartesian coordinates () ( ) z y x

Effects of Inhalation Transience on Particle Transport Through a CT-Based Human Airway Geometry

The effects of inhalation transience on particle transport through the lungs were examined using numerical simulation. Physiologically appropriate, regional ventilation was induced through a computed tomography (CT) based human airway geometry for steady and transient inhalation using lobar-specific boundary conditions. Transient inhalation and the analogous steady cases were simulated for two breathing rates. Particle transport was modeled for a range of particle sizes and Stokes numbers. The deposition fractions of particles were analyzed and comparisons were made between the results for steady and transient inhalation. Deposition fractions for particles released during transient inhalation were substantially less than those released during steady inhalation for all but the largest particle sizes. Future work is suggested.Copyright