Liutex-based vortex control with implications for cavitation suppression

Viewed as sinews and muscles of fluid motion,coherent vortical structures with their interactions are key to understanding the flow dynamics.Based upon this observation,we explore the possibility of efficient flow control by directly manipulating vortices numerically inside the flow field based on the vortex definition and identification system of Liutex.The objective is twofold:(1)to study the vortex dynamics,for example,by observing the response of the flow to strengthening or weakening of certain vortices,and(2)to obtain efficient vortex-based control strategies which might lead us to practical applications.In the present numerical study,the manipulating of vortices is achieved by introducing additional source(force)terms to the Navier-Stokes equations,which hereafter will be collectively called Liutex force field model.Methodologies including controlling the rotation strength and centripetal force of particular vortices are detailed in a flow past a cylinder with different control purposes at Reynolds number of 200.Further examples are provided with a cavitating flow around two-dimensional Clark-Y hydrofoil,with particular interests on cavitation suppression.It is illustrated particular vortex with cavitation encircled could be effectively suppressed.     

Parametric study of a new HOS-CFD coupling method

This paper presents a developed new coupled method which combined our in-house CFD solver naoe-FOAM-SJTU and naoe-FOAM-os with a potential theory High Order Spectral method(HOS).A parametric study of nonlinear wave propagation in computational fluid dynamics(CFD)zone is considered.Mesh convergence,time step convergence,time discretization scheme and length of relaxation zone are all carried out.Those parametric studies verify the steady of this new combined method and give better choice for wave propagation.The dissipation in propagation of nonlinear regular wave can be lower than 3%in static mesh,and less than 2%in overset grid mesh.Meanwhile,a LNG FPSO is put into the viscous wave tank to study the suitable size of CFD zone.To achieve a better solution with least calculating resources and best numerical results,the length of CFD zone is discussed.These parametric studies can give reference upon employment of the potential-viscous coupled method and validation of the coupled method.     

Liutex-based centripetal force field model for improving the resistance and wake performances of JBC ship sailing in calm water

For complex aerodynamic and hydrodynamic problems,the analysis of vortex is very important.The Liutex method is an eigenvalue-based method which is local,accura...     

A multi-fidelity surrogate modeling approach for incorporating multiple non-hierarchical low-fidelity data

Multi-fidelity (MF) surrogate models have been widely used in simulation-based design problems to reduce the computational cost by integrating the data with different fidelity levels. Most of the existing MF modeling methods are only applicable to the problems with hierarchical low-fidelity (LF) models, namely the fidelity levels of multiple LF models can be identified. However, the fidelity levels of the LF models that are obtained from different simplification methods often vary over the design space. To address this challenge, a non-hierarchical Co-Kriging modeling (NHLF-Co-Kriging) method that can flexibly handle multiple non-hierarchical LF models is developed in this work. In the proposed method, multiple LF models are scaled by different scale factors, and a discrepancy model is utilized to depict the differences between the HF model and the ensembled LF models. To make the discrepancy Gaussian process (GP) model easy to be fitted, an optimization problem whose objective is to minimize the second derivative of the prediction values of the discrepancy GP model is defined to obtain optimal scale factors of the LF models. The performance of the NHLF-Co-Kriging method is compared with the extended Co-Kriging model and linear regression MF surrogate model through several analytical examples and an engineering case. Results show that the proposed method selects more reasonable scale factors for the multiple LF models and provides more accurate MF surrogate models under a limited computational budget.     

Parametric study of Liutex-based force field models

The motion of fluid consists of different scales of coherent vortical structures.These vortical structures determine the characteristics of fluid motion and are key to understand fluid dynamics.In this paper,we study the fine control method of vortical structures based on the Liutex force field model.This is achieved by constructing a source term using Liutex and directly add it to the Navier-Stokes equations.To investigate the influence of the constructed Liutex force model on vortical structures,a flow past a cylinder at Reynolds number of 100 is numerically studied with different source term magnitude and region.The drag and lift forces on the cylinder,as well as the flow field near and behind the cylinder are compared and analyzed.Results show that Liutex force model can effectively strengthen or weaken the vortical structures based on different purpose.