Visualization of Turbulence Anisotropy in the In-cylinder Flow of Internal Combustion Engines

Turbulence anisotropy has a great influence on mixture formation and flame propagation in internal combustion engines. However, the visualization of turbulence in simulations is not straightforward; traditional methods lack the ability to display the anisotropic properties in the engine geometry. Instead, they use invariant maps, and important information about the locality of the turbulence anisotropy is lost. This paper overcomes this shortcoming by visualizing the anisotropy directly in the physical domain. Componentality contours are applied to directly visualize the anisotropic properties of turbulence in the three-dimensional engine geometry. Using an RGB (red, green, blue) color map, the three limiting states of turbulence (one-component, axisymmetric 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 post-processing workflow. This paper focuses on unsteady Reynolds-averaged Navier-Stokes equations methods and uses the RNG k-ϵ model in the simulations. Computational fluid dynamics simulations of the cold flow operation of a single-cylinder research engine demonstrate the strength of this visualization strategy. Different phases of engine operation were investigated using a barycentric map and back-projecting the colors into the physical domain. Thus, the visualization of turbulence anisotropy becomes more accessible since it is done directly in the engine geometry. By providing a deeper understanding of the turbulence properties, this method improves the design of engine geometries and the accuracy of mixture formation and combustion in simulations.