Unsteady RANS and detached eddy simulation of the multiphase flow in a co-current spray drying

A detached eddy simulation(DES) and a k-ε-based Reynolds-averaged Navier–Stokes(RANS) calculation on the co-current spray drying chamber is presented. The DES used here is based on the Spalart–Allmaras(SA) turbulence model, whereas the standard k-ε(SKE) was considered here for comparison purposes. Predictions of the mean axial velocity, temperature and humidity profile have been evaluated and compared with experimental measurements. The effects of the turbulence model on the predictions of the mean axial velocity, temperature and the humidity profile are most noticeable in the(highly anisotropic) spraying region. The findings suggest that DES provide a more accurate prediction(with error less than 5%) of the flow field in a spray drying chamber compared with RANS-based k-ε models. The DES simulation also confirmed the presence of anisotropic turbulent flow in the spray dryer from the analysis of the velocity component fluctuations and turbulent structure as illustrated by the Q-criterion.

Comparison of DES and URANS:Estimation of fluctuating pressure from URANS simulations in stilling basins

This study conducts a comparative analysis between detached eddy simulation(DES)and Unsteady Reynolds-averaged Navier-Stokes(URANS)models for simulating pressure fluctuations in a stilling basin,aiming to assess the URANS mode’s performance in modeling pressure fluctuation.The URANS model predicts accurately a smoother flow field and its time-average pressure,yet it underestimates the root mean square of pressure(RMSP)fluctuation,achieving approximately 70%of the results predicted by DES model on the bottom floor of the stilling basin.Compared with DES model’s results,which are in alignment with the Kolmogorov−5/3 law,the URANS model significantly overestimates low-frequency pulsations,particularly those below 0.1 Hz.We further propose a novel method for estimating the RMSP in the stilling basin using URANS model results,based on the establishment of a quantitative relationship between the RMSP,time-averaged pressure,and turbulent kinetic energy in the boundary layer.The proposed method closely aligns with DES results,showing a mere 15%error level.These findings offer vital insights for selecting appropriate turbulence models in hydraulic engineering and provide a valuable tool for engineers to estimate pressure fluctuation in stilling basins.