Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

Abstract

The present paper focuses on the numerical simulation of unsteady cavitation around a NACA66 hydrofoil to improve the understanding of the cavitation effects on hydraulic machinery. For this aim, the Zwart–Gerber–Belamri cavitation model was updated and uploaded as a library file for OpenFOAM’s solvers using C++ language. Furthermore, the hybrid Reynold average Navier–Stokes (RANS)–large eddy simulation (LES) model k - ω SST scale adaptive simulation (SAS) was implemented as a turbulence model for the present study of scale adaptive simulation. For validation, numerical results were compared with experimental results obtained by Leroux at the Naval Academy Research Institute in France. In order to highlight the benefits in terms of computational consumption and reproduction of the phenomenon the k - ω SST SAS model was compared against implicit large eddy simulation (ILES). Results show that the cavitation evolution including the maximum vapor length, the detachment and the oscillation frequency were reproduced satisfactorily using k - ω SST SAS. Moreover, k - ω SST SAS results predicted a lower total vapor volume on time than ILES, which is related to observed pulses of pressure coefficient, C p , and those match fairly well with the experimental results. To summarize, the k - ω SST SAS model predicts with good accuracy unsteady cavitation behavior around hydrofoils and shows improved versatility over the ILES approach.

Analysis of Applicability of CFD Numerical Studies Applied to Problem When Pump Working as Turbine

“…Finally, Open-FOAM benefited from being a free software package that could be adapted according to our specific needs [24], which gave it a significant advantage over the rest. To solve the RANS equations, the most used models in turbomachinery were k-ε and k-ω-SST (Figure 3b), which coincides with previous studies [22,25] due to the benefits they represent in terms of reproduction of flow phenomenon in PATs as well as computational consumption [18]. Furthermore, in these closure models, viscous effects were taken into account, allowing for greater accuracy of the results of numerical models.…”

“…Numerical simulations of PATs were based on a continuum mechanics approach for fluid mechanics [18]. For that, Navier-Stokes equations were solved using CFD methods.…”

“…Equations ( 1) and ( 2) enable the definition of the average behavior of flows inside of PATs in all of the CFD simulations and to simplify solving equations. The filtered approach is indicated as [18]:…”

“…According to Fecarotta et al [16], the CFD technique allows modellers to understand the field flows and the operating conditions for PATs with high accuracy and a low cost in comparison to other experiments. Therefore, the continuum considerations used in CFD to solve Navier-Stokes equations (NS) are the most common way to perform numerical simulation for hydraulic machinery [17,18]. However, the experimental part is necessary to calibrate CFD numerical models and to obtain reliable results in PATs under different optimization stages [15,[19][20][21].…”

“…RANS models aim to obtain the average behavior of the internal flows in PATs with a lightweight computational mesh and unstructured characteristics [19]. On the other hand, large-eddy structures inside of an impeller could be obtained using LES with a complex structured mesh and more use of computational resources than RANS [18].…”