Ales Alajbegovic

DVE: Direct vehicle exhaust flow measurement using head-type flowmeters

When exhaust emissions from a vehicle are measured, a flow rate is needed in addition to pollutant concentrations in order to calculate the mass emitted. The highly unsteady flow from an internal combustion engine presents measurement challenges to exhaust flowmeters, especially at idle. Mass measurement methods used in the past have gotten around this problem by a variable dilution scheme (CVS) that measures a different, more favorable flow, but reduces and can contaminate exhaust gas concentration levels. The flow measurement system described here makes possible a more accurate measure of the vehicle exhaust flow by means of a number of design features. This improves considerably the cost effectiveness and accuracy of emissions measurement techniques such as the Bag-Minidiluter sampling system and raw modal analysis.

Simulation of Multiphase Flows in Complex Geometry Using a Hybrid Method Combining the Multi-Fluid and the Volume-of-Fluid (VOF) Approaches

A computational method combining the multi-fluid and the Volume-of-Fluid (VOF) approaches is presented to simulate industrial multiphase flows in complex geometry. This method is particularly applicable for flows where well-defined interfaces between different phases/fluids co-exist with small-scale multiphase structures. The interfaces in relatively large scales (that can be accurately resolved on a computational mesh with a practical size) are tracked by the VOF method, whereas the small scale multiphase flow structures (that are too computationally expensive to be explicitly tracked by the VOF method) are accounted for by using the multi-fluid approach. In order to provide more computational flexibility, any two of the phases tracked by the multi-fluid approach can either have different velocities (two-fluid model) or share the same velocities (equilibrium model). The hybrid method presented here enables efficient simulation of complex flows with multiple phases/fluids on arbitrary-shaped unstructured meshes. It is fully implemented in the commercial CFD software, AVL FIRE/SWIFT. The governing equations are discretized based on a finite volume method (FVM) and the pressure field is obtained using the SIMPLE algorithm. The effect of surface tension is also included for the phases tracked by the VOF method using a Continuum Surface Force (CSF) model. Application to a well-established example of multiphase flow—a Taylor bubble rising inside a stagnant liquid—is presented to demonstrate the capability of the method.© 2002 ASME

Vehicle aerodynamics impact of on-road turbulence

The ultimate target for vehicle aerodynamicists is to develop vehicles that perform well on the road in real-world conditions. On the other hand, vehicle development today is performed mostly in controlled settings, using wind tunnels and computational fluid dynamics with artificially uniform freestream conditions and neglecting real-world effects due to road turbulence from the wind and other vehicles. Turbulence on the road creates a non-uniform and fluctuating flow field in which the length scales of the fluctuations fully encompass the length scales of the relevant aerodynamic flow structures around the vehicle. These fluctuations can be comparable in size and strength with the vehicle’s own wake oscillations. As a result, this flow environment can have a significant impact on the aerodynamic forces and on the sensitivity of these forces to various shape changes. Some aerodynamic devices and integral design features can perform quite differently from the way in which they do under uniform freestream conditions. In this paper, unsteady aerodynamics simulations are performed using the lattice Boltzmann method on a detailed representative automobile model with several design variants, in order to explore the effect of on-road turbulence on the aerodynamics and the various mechanisms that contribute to these effects.

Fast models for battery cooling system design

Fast running battery pack electrical and thermal models were created from electrical test data and battery geometry. These fast running models were used in simulating lifetime battery temperature and cooling performance. These models include the battery, the pack structure, cold plates, and the electrical behavior. The models are capable of being integrated into either 3D or 1D models. These fast battery models allow design changes to be thoroughly evaluated at each step in a vehicle program.

Numerical and Experimental Investigation of Temperature and Flow Field in a Full Vehicle

Accurate CFD simulation of full vehicle enables vehicle development specialists to gain access to detailed flow and temperature field for the entire vehicle and for arbitrary driving conditions. Information of that nature is invaluable to vehicle development and design since it leads to detailed understanding of the problem areas and pointers to how the design and performance can be improved from the thermal management perspective. Presented are simulations of the vehicle Renault Scenic II cruising at 60 kilometers per hour using PowerFLOW. The simulations were performed using a coupling between the flow solver PowerFLOW and the thermal simulation package PowerTHERM that accounts for conduction and radiation effects. The simulation results were compared with the test data for steady state forced convection case. In order to gauge the accuracy of the simulations, extensive validations were made with thermocouple data and flow measurements. Good agreement was observed between the simulation results and the measurements.Copyright

Nozzle Effects in Thermal Wind Tunnels

Presented is an investigation of the wind-tunnel nozzle effects on the thermal performance within passenger vehicle underhood area. The Lattice-Boltzmann Equation (LBE) based flow solver is coupled with the system tool to solve for airflow and temperature distribution around the passenger vehicle in the wind tunnel. Several simulations with different nozzle sizes were performed. The simulation results are compared with airflow, temperature, and heat exchangers heat rejection measurements in the thermal wind tunnel. Good agreement is observed confirming that nozzle geometry dominates the airflow around the vehicle. The results show that different nozzle sizes can produce flows that have almost the same macroscopic characteristics while at the same time have subtle differences that can be very important for the vehicle design.Copyright