WENO-Z Scheme Research Articles

Embedment of WENO-Z reconstruction in Lagrangian WLS scheme implemented on GPU for strongly-compressible multi-phase flows

It is a notoriously challenge problem for Lagrangian particle methods to solve compressible flows with strong discontinuities and large volume variations. To overcome the problems of numerical oscillations, an accurate and stable Lagrangian Weighted-Least-Square (LWLS) method embedded with WENO-Z scheme (LWLS-WENO-Z) is proposed. To further enhance the numerical accuracy and stability, the particle shifting technique, the multi-level local-refinement technique, and the interface repulsive force are appropriately employed in the numerical scheme. Moreover, the smooth and stable coupled particle method between the LWLS and Roe's Riemann solver (LWLS-RR) is considered for the comparisons, further demonstrating the merit of the proposed LWLS-WENO-Z scheme. To reduce the simulation time, parallel computing with a CUDA-based program for the proposed scheme is implemented on a single GPU. In the numerical experiments, several 1D/2D benchmarks are solved to test the accuracy of the proposed method. Particularly, the challenge 2D underwater explosion and the cavitation bubble collapse and jetting are numerically investigated. Compared to other reference solutions, the present coupled particle method demonstrates robustness and superior accuracy in simulating these strongly-compressible multi-phase flows.

Improvements to Enhance Robustness of Third-Order Scale-Independent WENO-Z Schemes

Improvements to Enhance Robustness of Third-Order Scale-Independent WENO-Z Schemes

New simple local smoothness indicators for fifth-order WENO schemes simulating compressible flows

For the WENO-Z scheme, the structure of the local smoothness indicators has a significant impact on the computational performance of the weighted essentially non-oscillatory scheme with a given global smoothness indicator. In this paper, a new class of two-parameter local smoothness indicators is constructed by combining the classical fifth-order WENO-JS and WENO-UD5 schemes and locally appending the coefficients of the higher-order terms of the new local smoothness indicators. A new WENO scheme, WENO-NSLI, is constructed using the global smoothness indicators of WENO-UD5. Numerical experiments show that the new scheme can achieve optimal accuracy at the critical point when the parameter (λ,μ)=(0.5,10) is taken and has a higher resolution than WENO-JS, WENO-Z, and WENO-UD5.

An Improved WENO-Z Scheme for Hyperbolic Conservation Laws with New Global Smoothness Indicator

The fifth-order WENO-Z scheme proposed by Borges et al., using a linear combination of low-order smoothness indicators, is designed to provide a low numerical dissipation to solve hyperbolic conservation laws, while the power q in the framework of WENO-Z plays a key role in its performance. In this paper, a novel global smoothness indicator with fifth-order accuracy, which is based on several lower-order smoothness indicators on two-point sub-stencils, is presented, and a new lower-dissipation WENO-Z scheme (WENO-NZ) is developed. The spectral properties of the WENO-NZ scheme are studied through the ADR method and show that this new scheme can exhibit better spectral results than WENO-Z no matter what the power value is. Accuracy tests confirm that the accuracy of WENO-Z with q = 1 would degrade to the fourth order at first-order critical points, while WENO-NZ can recover the optimal fifth-order convergence. Furthermore, numerical experiments with one- and two-dimensional benchmark problems demonstrate that the proposed WENO-NZ scheme can efficiently decrease the numerical dissipation and has a higher resolution compared to the WENO-Z scheme.

On the application of gradient based reconstruction for flow simulations on generalized curvilinear and dynamic mesh domains

Accurate high-speed flow simulations of practical interest require numerical methods with high-resolution properties. In this paper, we present an extension and demonstration of the high-accuracy Gradient-based reconstruction and α-damping schemes introduced by Chamarthi (2022) for simulating high-speed flows in generalized curvilinear and dynamic mesh domains with the freestream preservation property. In the first part of this paper, the algorithms are detailed within the generalized curvilinear coordinate framework, with a focus on demonstration through stationary and dynamic mesh test cases. It has been shown both theoretically and through the use of test cases that the conservative metrics, including their interpolation to cell interfaces, must be numerically computed using a central scheme that is consistent with the inviscid flux algorithm to achieve the freestream preservation property. The second part of the paper illustrates the efficacy of the algorithm in simulating supersonic jet screech by displaying its capability to capture the screech tones and accurately characterize the unsteady lateral flapping mode of a Mach 1.35 under-expanded supersonic jet, in contrast to the WENO-Z scheme which fails to do so at the same grid resolution. In the final part of the paper, the parallelizability of the schemes on GPU architectures is demonstrated and performance metrics are evaluated. A significant speedup of over 200× (compared to a single core CPU) and a reduction in simulation completion time to 34.5 h per simulation were achieved for the supersonic jet noise case at a grid resolution of 13 million cells.

A unified framework for non-linear reconstruction schemes in a compact stencil. Part 1: Beyond second order

Discretization of the convection term in a three-cell compact stencil has been widely used in Computational Fluid Dynamics (CFD) of engineering because the second-order interpolation scheme is considered to be more robust and algorithmically simple than very high-order schemes. However, according to Godnunov's theorem, it has never been trivial to design an accurate and oscillation-free discretization scheme in a compact stencil. Over decades, various kinds of schemes have been proposed to increase accuracy beyond second-order without producing non-physical numerical oscillations. Representative schemes are polynomial-based non-linear interpolations such as TVD (Total Variation Diminishing), NVD (Normalized Variable Diagram) and third-order WENO (Weighted Essentially Non-oscillatory); and non-polynomial-based interpolations including RBF (Radial Basis Functions), LDLR (Local Double Logarithmic Reconstruction) and Tangent of Hyperbola for INterface Capturing (THINC). Within the semi-discretization finite volume method, existing reconstruction schemes suffer from different issues to some extent. For example, existing TVD schemes tend to cause smearing, clipping and squaring effects. Most WENO schemes and inconsistent RBF schemes are not scale-invariant. Especially, the improved WENO-Z scheme is neither scale-invariant nor mesh-size-independent. Computationally expensive non-polynomial-based interpolations usually have singularity and are dependent on tunable parameters. Thus, this work reviews reconstruction schemes by reformulating or calculating the reconstructed boundary value in the normalised-variable space where the characteristics of reconstruction schemes can be read directly. Through the accuracy analysis and the induction of existing schemes, this work proposes a Unified Normalised-variable Diagram (UND) where the following properties of a reconstruction scheme can be given diagrammatically: 1) the second-order and the third-order accuracy condition, 2) the TVD and CBC (Convection Boundedness Criterion) constrain, 3) the ENO condition, 4) the High Resolution (HR) property, 5) and the numerical dissipation and anti-dissipation error.The proposed UND framework is firstly demonstrated by the improvement of the existing schemes with a shape-preserving TVD limiter and a scale-invariant WENO scheme. Then, by defining the normalised reconstruction operator, a brand-new scheme named ROUND (Reconstruction Operator on Unified Normalised-variable Diagram) is proposed. The ROUND scheme is devised by directly configuring the normalised reconstruction operator of favourable properties on UND. This work presents a dissipative ROUND scheme in which normalised reconstruction operators are fully in the dissipative region of UND, and a low-dissipative ROUND scheme where rigorously adjusted anti-dissipation errors are introduced. Different formulations of ROUND schemes are presented to show the flexibility of designing schemes within the UND framework. The proposed dissipative and low-dissipative ROUND schemes are evaluated via benchmark tests which show the superior performance of ROUND on accuracy and resolution. Especially, in some cases, the low-dissipative ROUND schemes obtain comparable and even better resolution than classic fifth-order WENO. The significance of this work is further demonstrated by the preliminary results of applying ROUND on the FDM-IBM (Finite Difference Method and Immersed Boundary Method) framework.

STREAmS-2.0: Supersonic turbulent accelerated Navier-Stokes solver version 2.0

We present STREAmS-2.0, an updated version of the flow solver STREAmS, first introduced in Bernardini et al. (2021) [1]. STREAmS-2.0 has an object-oriented design which separates the physics equations from the specific back-end, making the code more suitable for future expansions, such as porting to novel computing architectures or implementation of additional flow physics. Similarly to the previous version, STREAmS-2.0 supports NVIDIA-GPU and CPU back-ends. Additionally, this version features improvements of the input/output data management, new energy and entropy preserving schemes for the discretization of the convective fluxes, recycling/rescaling inflow boundary condition, and a model for thermally perfect gases with variable specific heats. New version program summaryProgram Title: STREAmSCPC Library link to program files:https://doi.org/10.17632/hdcgjpzr3y.2Developer's repository link:https://github.com/STREAmS-CFD/STREAmS-2Licensing provisions: GPLv3Programming language: Fortran, CUDAJournal reference of previous version: M. Bernardini, D. Modesti, F. Salvadore, and S. Pirozzoli. STREAmS: a high-fidelity accelerated solver for direct numerical simulation of compressible turbulent flows. Comput. Phys. Commun. 263 (2021) 107906.Does the new version supersede the previous version?: Yes.Reasons for the new version: New code structure and release of new features.Summary of revisions:•The original solver [1] has been rewritten following an object-oriented design implemented through Fortran derived types that include variables and type bound procedures. The new software architecture has been designed to increase modularity and extensibility of the code, allowing users to add new back-ends and physics equations while maintaining the same code structure. This allows users to reuse portions of the code that are independent of the physics equations, the back-end, or both. The layer of computing procedures maintains a lean structure that can be highly optimized with respect to the implemented back-end.•Input handling is now based on the classic .ini format improving both user readability and input data management.•A family of new kinetic energy and entropy preserving schemes (KEEP) are now available and can be selected for stable, non-dissipative and accurate spatial discretization of the convective terms of the Navier–Stokes equations in smooth flow regions [2]. Concerning the shock-capturing flux, the improved low-dissipative WENO-Z scheme proposed by [3] is now available.•New inflow boundary conditions based on the recycling/rescale approach [4] have been implemented for the simulation of spatially evolving compressible turbulent boundary layers. Moreover, a new inflow condition based on the solution of the compressible Blasius equation is available to take into account the case of laminar boundary layers.•The constitutive relations have been generalized to take into account thermally perfect gases with variable specific heats, approximated with polynomial functions of the temperature that can be specified by the user [5].•A new stretching function has been implemented to improve the distribution of grid nodes for the computation of wall-bounded turbulent flows. The formulation blends uniform near-wall spacing with uniform resolution in terms of Kolmogorov units in the outer wall layer, guaranteeing accuracy with higher computational efficiency [6].Nature of problem: The code solves the compressible Navier–Stokes equations in Cartesian coordinates for a thermally perfect gas. The solver is designed for direct numerical simulation (DNS) of compressible supersonic turbulent boundary layers and various canonical configurations are supported, including turbulent channel flow, laminar and turbulent boundary layer and shock-wave/boundary layer interaction.Solution method: The equations are discretized using high-order finite difference approximations with hybrid low-dissipative/shock-capturing capabilities and the time advancement is performed using a Runge–Kutta scheme.

A New Third-Order Finite Difference WENO Scheme to Improve Convergence Rate at Critical Points

In this work, a new, improved third-order finite difference weighted essentially non-oscillatory scheme is presented for one- and two-dimensional hyperbolic conservation laws and associated problems. The parameter p which is regulate dissipation is introduced in the nonlinear weights in the framework of the conventional WENO-Z scheme, and the higher-order global smoothness indicator is obtained by the idea of Wang [Wang, Y. H., Y. L. Du, K. L. Zhao and L. Yuan. 2020. ‘A Low-dissipation Third-order Weighted Essentially Nonoscillatory Scheme with a New Reference Smoothness Indicator’. International Journal for Numerical Methods in Fluids. 92 (9): 1212–1234.], the sufficient condition of nonlinear weights is proved by using Taylor expansions. Finally, the value range of parameter p is obtained. The proposed scheme is verified to achieve the optimal order near critical points by linear convection equations with different initial values, and the high-resolution characteristic of the present scheme is proved on a variety of one- and two- dimensional standard numerical examples. Numerical results demonstrate that the proposed scheme gives better performance in comparison with the other third-order WENO schemes.

A New Mapped WENO Method for Hyperbolic Problems

In this study, a new family of rational mapping functions gRM(ω;k,m,s) is introduced for seventh-order WENO schemes. gRM is a more general family of mapping functions, which includes other mapping functions such as gM and gIM as special cases. The mapped WENO scheme WENO-IM(2,0.1), which uses gIM, performs excellently at fifth order but rather poorly at seventh order. The reason for this loss of accuracy was found to be the over-amplification of very small weights by the mapping process, which can be traced back to the large slope of gIM at ω = 0. For m > 1, gRM can be designed to have a unit slope at ω = 0, which will preserve small weights with little to no amplification. It has been demonstrated through several one-dimensional linear advection test cases that the mapped WENO scheme WENO-RM(6,3,2 × 103), which uses the mapping function gRM(ω;6,3,2 × 103), outperforms both WENO-M and WENO-IM(2,0.1) at seventh order. The proposed scheme also performs better at a number of one-dimensional inviscid gas flow problems compared to other popular WENO schemes such as the WENO-Z scheme.

Third-order scale-independent WENO-Z scheme to achieve optimal order at critical points

Our past work has shown that when the critical points occur within grid intervals, the relations of accuracy of the smoothness indicators of weighted essentially non-oscillatory schemes (WENO) reported by Jiang and Shu differ from those that are obtained by assuming that the critical points occur on the grid nodes. The global smoothness indicator in the WENO-Z scheme might accordingly differ from the original one. We use this understanding to first discuss several issues regarding current improvements to third-order WENO-Z (e.g., WENO-NP3, -F3, -NN3, and -PZ3), i.e., numerical results with scale dependence, the validity of the analysis by assuming that the critical points occur on the nodes, and sensitivity in terms of the computational time step and initial conditions through the examination of the order of convergence. Numerical simulations and analyses were used to highlight defects in these improvements that occur either due to the scale dependence of the results, or the failure to recover the optimal order when the critical points occur on the half-nodes. Following this, a generic analysis that assumes that the first-order critical points occur within the grid intervals is provided. The theoretical results thus derived are used to propose two scale-independent third-order WENO-Z schemes that can be used to attain the optimal order at the critical points. The first scheme is obtained by extending a downstream smoothness indicator to derive a new global smoothness indicator and incorporating it into the mapping function. The second scheme is achieved by extending another smoothness indicator and using a different global indicator. The following validations are chosen and tested: the typical 1D problem of scalar advections, and 1D and 2D problems based on Euler's equations. The results verify the capability of the proposed schemes to recover the optimal order at the critical points. Moreover, the first of the above two proposed schemes outperforms the improved third-order WENO-Z scheme in terms of numerical resolution and robustness, which is usually favored by applications.

High order weighted essentially non-oscillatory WENO-ZN schemes for hyperbolic conservation laws

In Shen et al. (2020), the authors have proposed a novel weighting method to construct the fifth-order WENO-ZN scheme to improve the accuracy at the second-order critical point. Its basic idea is that, the square of the fourth-order undivided difference on the global five-point stencil used by the fifth-order WENO scheme is suggested as the global smoothness indicator. To keep the ENO property and enhance robustness for resolving shock waves, the constant 1 used to calculate the un-normalized weights in the original WENO-Z schemes is replaced by an adaptive function, which can approach a small value if the global stencil contains a discontinuity or approach a large value if the solution is smooth enough. The fifth-order WENO-ZN scheme can obtain fifth order accuracy at both the first- and second-order critical points. However, limited by the smoothness indicators, the scheme cannot improve the convergence rate at the third-order and above critical points. In this paper, we extend the idea of the fifth-order WENO-ZN scheme to construct higher-order WENO-ZN schemes and investigate their performance. Numerical experiments show that the (2r−1)th-order (r≥3) WENO-ZN schemes are robust for capturing shock waves and can improve the accuracy order in smooth regions including the maximum (2r−4)th-order critical points.

Application of High-Order WENO Scheme in the CFD/FW–H Method to Predict Helicopter Rotor Blade–Vortex Interaction Tonal Noise

The accurate prediction of helicopter rotor blade–vortex interaction (BVI) noise is challenging. This paper presents an implementation of the seventh-order improved weighted essentially non-oscillatory (WENO-Z) scheme for predicting rotor BVI noise using a high-resolution numerical method based on the Reynolds-averaged Navier–Stokes and the Ffowcs Williams–Hawkings equations. The seventh-order improved WENO-Z scheme is utilized to minimize the inherent numerical dissipation of the reconstruction method in the monotone upstream-centered scheme for conservation laws (MUSCL), thereby improving the rotor wake resolution and the BVI noise-prediction accuracy. The three-layer dummy cell method is used to ensure that the flux at the boundary maintains seventh-order accuracy. The effectiveness of the flow solver and the acoustic solver is validated using the Helishape-7A rotor and the UH-1H rotor, respectively. The flow field and BVI noise characteristics of the OLS rotor obtained from the fifth- and seventh-order WENO-Z schemes are compared with that of the third-order MUSCL for coarse and fine background grids. The wake resolution, noise-prediction accuracy, and computational cost of the three schemes are compared. The results show that the high-order WENO scheme provides higher accuracy for flow field simulation and BVI noise prediction than the MUSCL, but the computational cost of the WENO scheme increases substantially as the grid resolution increases. However, the WENO scheme can predict BVI using a coarser grid than the MUSCL. The computational cost of the WENO scheme is relatively low under the same flow field simulation resolution.

Novel weighted essentially non-oscillatory schemes with adaptive weights

In this paper, by constructing a selector that can identify the less-smooth sub-stencils, we have improved the classical WENO-JS and WENO-Z schemes, and developed two new WENO schemes which can adaptively increase the weight of less-smooth sub-stencils, WENO-IJS and WENO-IZ. Theoretical analysis shows that the present schemes maintain essentially non-oscillatory (ENO) property and have lower numerical dissipation at discontinuities. The investigation of approximate dispersion relation analysis (ADR) shows that the spectral characteristics of the present schemes are better than those of the classical WENO-JS, WENO-Z and WENO-Z+ schemes. A series of numerical experiments show that the shock wave capture capability and resolution of the complex process structure of the present schemes are significantly better than WENO-JS, WENO-Z and WENO-Z+.

An Improved 3rd-Order WENO Scheme Based on a New Reference Smoothness Indicator

In order to meet the requirement of high accuracy and high resolution in computational fluid dynamics (CFD), a new reference smoothness indicator was proposed to reduce the numerical dissipation of the classical 3rd-order weighted essentially non-oscillatory (WENO) scheme. The construction method is different from the classical WENO-Z scheme. It is obtained through the <i>L</i>²-norm approximation of the derivatives of the reconstruction polynomials of the whole global stencil, and the linear combination of the derivatives of the reconstruction polynomials on the candidate sub-stencils. With this calculation method, higher-order reference smoothness indicators can be obtained than the WENO-Z scheme. In addition, different reference smoothness indicators can be obtained by change of the value of free parameter $ \varphi$. A series of numerical examples prove the effectiveness of the reference smoothness indicator.

A high-resolution finite volume scheme based on optimal spectral properties of the fully discrete scheme with minimized dispersion and adaptive dissipation

For the compressible flows with broadband length scales, a high-resolution scheme based on the finite volume method with minimized dispersion and adaptive dissipation is proposed, which is capable of capturing the small-scale flow details and discontinuities. Firstly, the dispersion property is optimized for the fully discrete scheme, and the minimized dispersion parameters for different Courant numbers are obtained. Then, the dispersion-dissipation condition and a scale sensor are employed to get the critical dissipation parameter which not only can suppressed the numerical oscillations but also can keep the dissipation as low as possible to capture more flow details. Moreover, the critical dissipation isosurface is constructed to develop the functional relationship between the dissipation and the estimated scaled wavenumber. To have the capability of capturing shock waves, the proposed scheme is blended with the optimized WENO-Z scheme to form the hybrid scheme. Finally, several benchmark test cases are employed to verify the high-resolution properties and the robustness of the scheme proposed in the present paper. Futhermore, more high-fidelity solutions obtained by the proposed scheme for some numerical simulations with complex geometric configurations are expected.

A new fifth-order symmetrical WENO-Z scheme for solving Hamilton-Jacobi equations

This research describes a new fifth-order finite difference symmetrical WENO-Z scheme for solving Hamilton-Jacobi equations. This method employs the same six-point stencil as the original fifth-order WENO scheme (SIAM J. Sci. Comput. 21 (2000) 2126--2143) and a new WENO scheme recently proposed (Numer. Methods Partial Differential Eq. 33 (2017) 1095--1113), and could generate better results and create the same order of accuracy in smooth area without loss of accuracy at critical points simultaneously avoiding incorrect oscillations in the vicinity of the singularities. The new reconstruction is a convex combination of a fifth-order linear reconstruction and three third-order linear reconstructions. We prepare a detailed analysis of the approximation order of the designed WENO scheme. Some benchmark tests in 1D, 2D and 3D are performed to display the capability of the scheme.

High-order weighted compact nonlinear scheme for one- and two-dimensional Hamilton-Jacobi equations

This paper designs a fifth-order weighted compact nonlinear scheme (WCNS) on a five-point stencil to solve one- and two-dimensional Hamilton-Jacobi equations. The five-point WCNS is used to compute the left and right limits of first-order spatial derivatives of the HJ equations in the Lax-Friedrichs monotone numerical Hamiltonian. The WENO-Z type interpolation for cell-edge values of the solutions is used to suppress numerical oscillations which may appear near discontinuities. Five- and seven-point WENO-Z schemes for Hamilton-Jacobi equations are also designed for comparisons. The performance of the WCNS and the two WENO-Z schemes is demonstrated by several numerical examples in one-dimensional and two-dimensional cases.

An improved WENO-Z+ scheme for solving hyperbolic conservation laws

Increasing the weight of the less-smooth substencil is an effective way to improve the resolution of the WENO scheme. Based on this knowledge, Acker et al. (2016) [14] constructed the WENO-Z+ scheme by introducing a novel term, which has a role of increasing the weight of the less-smooth substencil, into the WENO-Z weight formula. In this paper, we propose a set of modifications to WENO-Z+ scheme to give full play to its potential in spectral properties, resulting the WENO-Z+M scheme. WENO-Z+M shows excellent spectral properties. In the numerical tests, the resolution of the fifth-order WENO-Z+M scheme is significantly higher than those of the ninth-order WENO-Z scheme and the state-of-art fifth-order WENO scheme (Zhu and Hu, 2020 [25]). This paper also reveals the unique performance of the WENO-Z+ type schemes. The previous WENO schemes always have spectral properties and accuracy inferior to those of the underlying linear schemes. In contrast, by assigning weights greater than the corresponding ideal weights to the less-smooth substencils, WENO-Z+ type schemes can achieve spectral properties and accuracy superior to the underlying linear scheme.

Improved weighted NND scheme for shock-capturing

Aimed at decreasing the numerical dissipation of weighted non-oscillatory and non-free-parameter dissipation (WNND) scheme, we present an improved counterpart for shock-capturing. The new algorithm is based on the framework of Z-type weighting procedure with new local and global smoothness indicators. The performances of the proposed scheme are evaluated on several numerical tests governed by one-dimensional Euler equations. Numerical results indicate that the improved WNND scheme has advantages over the original WNND and third-order WENO-JS and WENO-Z schemes.

Improvement of the WENO-Z+ scheme

The WENO-Z+ scheme (J. Comput. Phys. 2016, 313: 726-753) was obtained by adding a new term into the WENO-Z weights. The added term has the role of raising the weights of less-smooth substencils. The WENO-Z+ scheme achieves superior results in the test problems that involve only a single wave component. For problems containing multiscale structures, however, the results of WENO-Z+ show little improvement compared with those of WENO-Z. In this short note, we investigate the reason why WENO-Z+ has little improvement in solving the multiscale problems and propose a set of modifications to it. A series of numerical tests confirm that the new scheme, which is named WENO-Z+I, has significantly improved multiscale resolution. The multiscale resolution of the fifth-order WENO-Z+I scheme is even significantly better than that of the seventh-order WENO-Z scheme. We also find that the WENO-Z+ type schemes can achieve better spectral properties than the corresponding linear upwind scheme.