Appropriate Level of Simulation in Tumble Port Evaluation

This presentation was made at NAFEMS Americas Seminar "Engineering Analysis & Simulation in the Automotive Industry: Creating the Next Generation Vehicle Accurate Modelling for Tomorrow's Technologies".

The automotive engineering community is now confronting the largest technology transformation since its inception. This includes the electrification of powertrains for more efficient consumption and cleaner emissions, the reinvention of the battery with fast wireless charging capabilities and finally the advent of a fully autonomous vehicle. Compounding to these technology changes, the automotive companies design verification process is moving away from a major reliance on physical testing to almost a full virtual simulation product verification process. The challenges to the automotive engineers are enormous and require a significant increase in the upfront use of numerical simulation capabilities, methods and processes such they’re able to efficiently design, manufacture and deliver these very innovative technologies to the market in greater speeds than ever before.

Resource Abstract

Simulation software vendors are promoting advances in software usability to advance the use of simulation tools into the hands of designers and design engineers. While this can increase the amount of simulation that is performed during product development, it can call into question the accuracy of the simulation results when that simulation is taken out of the hands of the analysis expert. Thus, the concern arises of speed/quantity vs. accuracy. However, it is most important to focus on the design question that is being answered by the simulation. That is, do you need an accurate result or do you need a reliable comparison? This presentation illustrates one example of defining the analysis requirements and applying the appropriate level of simulation (published by the authors as SAE paper 2016-01-0636).

This work focused on intake port development for cylinder heads of spark-ignition engines. Tumble characteristics are generated by a combination of intake port geometry, valve lift and timing, and piston motion. While attempts to characterize tumble from steady-state cylinder head flow benches have been the traditional approaches, the ability to correlate the results to operating engines is limited. Very limited research has been published since 2000 – around the same time simulation began to take hold throughout engine development. The only available methods that account for both piston motion and valve lift are detailed computational fluid dynamic (CFD) analysis or optical measurements of flow velocity. Southwest Research Institute performs extensive combustion and charge air motion CFD using a moving boundary (adaptive mesh) under transient conditions. However, the complexity of this type of simulation makes it reserved for engine CFD experts. Additionally, the time required to set up, perform and post-process this analysis limits the amount of design iterations that can be evaluated. These approaches are too resource intensive for rapid comparative assessment of multiple port designs.

The objective of this research was to develop a methodology to rapidly assess comparative intake port designs for their capability to produce tumble motion within the combustion chamber. In an engine development program, using this comparison, only the optimum design would then be submitted to the CFD expert for final tumble flow evaluation using moving boundary transient analysis to achieve accurate results of all air flow parameters desired.

Based on the best features of current steady-flow testing, a simplified computational approach was identified to account for the important effects of the moving piston. The method was compared to moving-boundary CFD analysis. After some refinement, this method could consistently rank the tumble performance of comparative port designs and lead to the same conclusions as predicted with moving-boundary CFD simulation. Total resource requirements were less than one third that of the moving-piston analysis for the same engine.

Document Details

AuthorMegel. A
Date 8th November 2018
OrganisationSouthwest Research Institute


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