Abstract
The existing definition method of filter grid scale in a Detached Eddy Simulation (DES) hybrid model is unreasonable, which will lead to the unreasonable trigger of a boundary layer large eddy simulation and reduce computational efficiency. In view of this problem, the filter grid scale is discussed in this paper. The 90° square curved elbow is selected as the research object. The effects of three grid definition methods: geometric mean (ΔGM), arithmetic mean (ΔAM) and quadratic mean (ΔQM) on the simulation results of the DES model are compared, and the velocity distribution of the flow cross section and the distribution of the flow pressure coefficient on the outer arc surface are compared with the experimental results of Taylor. The results show that the order of the three definition methods is ΔGM≤ΔAM≤ΔQM. Meanwhile, within 30° < polar angle(θ) < 75°, the results are closer to the experiment, and the development trends and numerical values of ΔAM and ΔQM are closer to the experiment in general. However, when θ > 60°, the value of ΔQM is slightly closer to the experimental result than ΔAM. ΔQM is more suitable for calculating the internal flow in a curved elbow than the other two methods.
Highlights
The turbulence inside the centrifugal pump shows unstable flow phenomena due to curvature and rotation
For the three filtering grid scales, the effects of definition methods (∆AM, ∆GM and ∆QM ) on calculation results in the Detached Eddy Simulation (DES) model were compared to the experimental results
In the inlet section of the elbow, the three velocity curves are still close to the experimental value, which indicates that the three scale definition methods can accurately simulate the characteristics of the internal flow distribution
Summary
The turbulence inside the centrifugal pump shows unstable flow phenomena (flow separation and secondary flow) due to curvature and rotation. According to the processing scales for turbulence in the Navier–Stokes (N-S) Equation [1], there are mainly three kinds of method, that are Direct Numerical Simulation (DNS), Reynolds Average Navier–Stokes (RANS) and Large Eddy Simulation (LES). LES needs to build a very fine grid to simulate a large number of small-scale fluctuations in the near-wall region, resulting in a huge amount of calculations for complex three-dimensional flow [5]. The RANS/LES hybrid model methods mainly include Detached Eddy Simulation (DES) [6] and Scale-Adaptive Simulation (SAS) [7]. The IDDES method can improve the calculation accuracy in the boundary layer, the introduced WMLES means there is a complete LES method within the whole flow field In a sense, this contradicts the original intention of DES-type models (RANS in the boundary layer and LES in other regions). The effects of three definition methods on the simulated results were compared to the experimental results of the 90◦ curved elbow
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