Reply to Discussion by Duarte et al. of “CFD analysis of the effect of nozzle stand-off distance on turbulent impinging jets”

Abstract

The authors would like to thank the discussants for their interesting suggestions. The discussants have carried out experiments on impinging jets and have compared their results with the CFD results presented in the paper. In addition, discussants have also presented a solution for the differences observed between the CFD and experimental results in the core portion of the jet.The discussants' experiment includes measurements on impinging water jets with a 72 mm diameter (D) circular nozzle and a stand-off distance of H/D = 9.58. Issuance velocities ranged from 5 to 22 m/s. The discussants have also questioned the use of Reynolds Stress Model (RSM) for modeling the turbulence in the paper. Herein, the reasons for choosing this turbulence model in our simulations are explained.Based on the H/D ratio, different regimes occur in the flow field of impinging jets ( Fig. 1 from Shademan et al. 2013). For H/D < 6 it has been found that the core of the jet is still developing on reaching the plate surface (Nishino et al. 1996;Hadziabdic and Hanjalic 2008). For larger impingement heights (H/D > 8), Rajaratnam (1974, 1977) The purpose of the paper was also to identify some of the issues and difficulties associated with previously used turbulence models in solving turbulent flow in impinging jets.Numerical simulation of a circular impinging jet using RANS simulations has been of interest to many researchers. As a result, these simulations formed part of the 2nd ERCOFTAC-IAHR Workshop on Refined Flow Modelling in 1993. Later, Craft et al. (1993) published their research on impinging jets using different turbulence models. They reported that due to the weakness associated with the eddy viscosity stress-strain relationship in the turbulence models, the results were not in good agreement with the available experimental data. Similar issues were reported by Cooper et al. (1993), who reported that the k-model over-predicts the turbulent kinetic energy near the stagnation point.To sort out the issues reported by previous researchers in modeling impinging jets, different turbulence models were implemented in the current study. Models that take into account the low-Re effects in the flow were selected. In addition, the selected models take into consideration the anisotropic nature of the turbulent viscosity, which is ignored during Reynolds averaging. The Realizable k-model (Shih et al. 1995), the k-SST (Shear Stress Transport) model (Menter 1994), and the Reynolds Stress Model (RSM) (Launder et al. 1975) were implemented in the simulations.Each of the commonly used turbulence models has some advantages and disadvantages. Considering that RSM is a fully anisotropic turbulence model, which solves the transport equations for all three fluctuating velocity components, the issues resulting from applying the Boussinesq approximation is removed. Basically, the strength of this model compared to the Boussinesq based turbulence models is its capability in producing the fluctuating velocity components in the results. The other reason fo...