Visualization of Turbulence Anisotropy in the In-cylinder Flow of Internal Combustion Engines 2020-01-1105
Anisotropy is one of the most important characteristics of turbulent flows. In internal combustion engines, anisotropy significantly influences processes such as mixture formation and flame propagation. There are many different visualization strategies in the literature that make the impact of anisotropy on specific parameters more accessible for analysis. However, traditional methods are unable to display anisotropy directly in the physical domain. Instead, they use invariant maps, leading to the loss of important information. Thus, interpretation of the results becomes difficult especially when a large number of data points exist.
This paper overcomes this shortcoming by visualizing turbulence anisotropy directly in the physical domain. Through the application of componentality contours, the anisotropic properties of turbulence in the three-dimensional engine geometry are directly visualized; the focus is on non-reactive flows. However, the methodology can easily be extended to reactive flows. By using an HSV (hue, saturation and value) color map, the three limiting states of turbulence (one-component, two-component and isotropic turbulence) are displayed in the three-dimensional physical domain. Thus, the assessment and interpretation of the results is straightforward and can easily be integrated into a normal postprocessing workflow.
Computational Fluid Dynamics (CFD) simulations of cold flow operation of a passenger car-sized single-cylinder research engine were carried out using the commercial CFD tool Converge. A user-defined function (UDF) was written to calculate the anisotropy stress tensor and the color components of the limiting states of turbulence. The visualization technique is applied to investigate the different regimes of the in-cylinder flow during the intake and compression strokes with a particular emphasis on the evolution of tumble motion in the cylinder. Visualizations and a thorough discussion about the nature of turbulence in these investigations are provided. In the future, this simple tool will help to improve engine geometry, combustion and the accuracy of mixture formation prediction.
Rajat Soni, Clemens Gößnitzer, Gerhard Pirker, Andreas Wimmer
LEC GmbH, Graz University of Technology