Modeling Standards and Recommendations
As the result of findings from ECN1 and plans for modeling contributions to ECN2, most groups have now picked metrics that will be used for comparison of modeling results. CFD activities should be performed and post-processed according the following standard definitions and recommendations.
- Cd, Cv and Ca nozzle flow coefficients: The value of the density which is used for the calculation is to be reported.
- Liquid penetration: Maximum distance from the nozzle outlet to the farthest axial position for 0.1% liquid volume fraction, averaged over a volume of 1 mm in diameter and 1 mm in axial length.
- Vapor penetration: Maximum distance from the nozzle outlet to where the fuel mass fraction (or mixture fraction) is 0.1%.
- High-temperature ignition delay: Two different definitions are utilized. (1)First time at which Favre-average OH mass fraction reaches 2% of the maximum in the domain after a stable flame is established. (2) The time of maximum gradient dT/dt in temperature.
- Flame lift-off length: First axial location of Favre-average OH mass fraction reaching 2% of its maximum in the domain.
For consistency in comparison, we recommend similar simulation baselines (boundary conditions, grid, physical models) as defined in modeling contributions to ECN2. For RANS Lagrangian spray computations, we recommend minimum cell sizes (0.25 mm) and time steps (dt = 5E-7 s) in order to ensure fairly converged and comparable spray results.