Novel Metrics for Validation of PIV and CFD in IC Engines

Abstract

In-cylinder flow motion has a significant effect on mixture preparation and combustion. Therefore, it is vital that CFD engine simulations are capable of accurately predicting the in-cylinder velocity fields. Highspeed planar Particle Image Velocimetry (PIV) experiments have been performed on a single-cylinder GDI optical engine in order to validate CFD simulations for a range of engine conditions. Novel metrics have been developed to quantify the differences between experimental and simulated velocity fields in both alignment and magnitude. The Weighted Relevance Index (WRI) is a variation of the standard Relevance Index that accounts for the local velocity magnitudes to provide a robust comparison of the alignment between two vector fields. Similarly, the Weighted Magnitude Index (WMI) quantifies the differences in the local magnitudes of the two velocity fields. The WRI and WMI are normalised and combined to produce a combined metric, the Combined Magnitude and Relevance Index (CMRI), that quantifies the differences between two flow fields in both magnitude and alignment simultaneously.PIV measurements were made every 5°ca in the central tumble plane during the induction and compression strokes. The WRI, WMI and CMRI metrics are used to validate numerical simulations of the motored in-cylinder flow measured with PIV for a range of valve lift profiles and engine speeds.

Manifold reduction techniques for the comparison of crank angle-resolved particle image velocimetry (PIV) data and Reynolds-averaged Navier-Stokes (RANS) simulations in a spark ignition direct injection (SIDI) engine

“…A variable timestep is applied during the simulation, and more details about the numerical setup and models used in the study can be found in a previous work. 38 The working fluid in the simulation is chosen as air, which is treated as an ideal gas. Several initial and boundary conditions are adopted directly from the experimental measurements, namely: intake and exhaust valve lifts pressures within the inlet and exhaust runners time-averaged intake, exhaust and main engine coolant temperatures time-averaged intake air volume flow rate…”

Quantitative metrics for comparison of in-cylinder velocity fields using particle image velocimetry

“…The metrics are used to determine a representative mean cycle, to rapidly identify single cycles that provide the best and worst matches to this mean cycle and to quantify the spatial distribution of variability across the tumble plane. For application of these metrics to mean flow fields for validation of CFD simulations using PIV across multiple engine operating points the reader is directed to Scott et al (2019).…”

Multi-Plane PIV Measurements in a Gasoline Direct Injection Engine

“…The CFD package used linear interpolation between the cell locations to output velocity vectors at the locations of the PIV measurements, due to the minimum cell spacing of 0.7 mm. Comparisons between the tumble ratio predicted by the CFD and the ensemble averaged PIV values have been presented already [23].…”

“…For details of the WRI, WMI and CMRI metrics and their application to analysis of flow fields the reader is directed to [22], [23]. A brief summary is provided here for convenience.…”

“…However, the RI can be overly sensitive to the alignment of regions of low velocity such as the tumble vortex center, where even small differences in the locations of the vortex center between the modelled and measured data can result in very low values of the RI. Recent work ( [22], [23]) has used a weighted function of the local velocity to provide a Weighted Relevance Index (WRI). The same type of approach has been applied to comparison of the magnitudes with a Weighted Magnitude Index (WMI).…”