Flux limiter - Citizendia

Flux limiters are used in high resolution schemes — numerical schemes used to solve problems in science and engineering, particularly fluid dynamics, described by partial differential equations (PDE's). High-resolution schemes are used in the numerical solution of Partial differential equations where high accuracy is required in the presence of shocks or discontinuities Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion In Mathematics, partial differential equations ( PDE) are a type of Differential equation, i They are used in high resolution schemes, such as the MUSCL scheme, to avoid the spurious oscillations (wiggles) that would otherwise occur with high order spatial discretisation schemes due to shocks, discontinuities or sharp changes in the solution domain. MUSCL stands for Monotone Upstream-centered Schemes for Conservation Laws, and the term was introduced in a seminal paper by Bram van Leer (van Leer 1979 Use of flux limiters, together with an appropriate high resolution scheme, make the solutions total variation diminishing (TVD). In systems described by Partial differential equations such as the following hyperbolic Advection equation, \frac{\part u}{\part t} + a\frac{\part u}{\part

Note: Flux limiters are also referred to as slope limiters because they both have the same mathematical form, and both have the effect of limiting the solution gradient near shocks or discontinuities. In general, the term flux limiter is used when the limiter acts on system fluxes, and slope limiter is used when the limiter acts on system states. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks

1 How they work
2 Limiter functions
- 2.1 Generalised minmod limiter
3 See also
4 References
5 Further reading

How they work

The main idea behind the construction of flux limiter schemes is to limit the spatial derivatives to realistic values - for scientific and engineering problems this usually means physically realisable values. They are used in high resolution schemes for solving problems described by PDE's and only come into operation when sharp wave fronts are present. High-resolution schemes are used in the numerical solution of Partial differential equations where high accuracy is required in the presence of shocks or discontinuities For smoothly changing waves, the flux limiters do not operate and the spatial derivatives can be represented by higher order approximations without introducing non-real oscillations. Consider the 1D semi-discrete scheme below,

$\frac{d u_i}{d t} + \frac{1}{\Delta x_i} \left[ F \left( u_{i + \frac{1}{2}} \right) - F \left( u_{i - \frac{1}{2}} \right) \right] =0$ .

where, $F \left( u_{i + \frac{1}{2}} \right) \$ and $F \left( u_{i - \frac{1}{2}} \right) \$ represent edge fluxes for the ith cell. If these edge fluxes can be represented by low and high resolution schemes, then a flux limiter can switch between these schemes depending upon the gradients close to the particular cell, as follows,

$F \left( u_{i + \frac{1}{2}} \right) = f^{low}_{i + \frac{1}{2}} - \phi\left( r_i \right) \left( f^{low}_{i + \frac{1}{2}} - f^{high}_{i + \frac{1}{2}} \right)$ ,

$F \left( u_{i - \frac{1}{2}} \right) = f^{low}_{i - \frac{1}{2}} - \phi\left( r_{i-1} \right) \left( f^{low}_{i - \frac{1}{2}} - f^{high}_{i - \frac{1}{2}} \right)$ ,

where,

$f^{low} = \$ low resolution flux,

$f^{high} = \$ high resolution flux,

$\phi\ (r) = \$ flux limiter function,

and $r\$ represents the ratio of successive gradients on the solution mesh, i. e. ,

$r_{i} = \frac{u_{i} - u_{i-1}}{u_{i+1} - u_{i}}$ .

The limiter function is constrained to be greater than or equal to zero, i. e. , $r \ge 0$ . Therefore, when the limiter is equal to zero (sharp gradient, opposite slopes or zero gradient), the flux is represented by a low resolution scheme. Similarly, when the limiter is equal to 1 (smooth solution), it is represented by a high resolution scheme. The various limiters have differing switching characteristics and are selected according to the particular problem and solution scheme. No particular limiter has been found to work well for all problems, and a particular choice is usually made on a trial and error basis.

Limiter functions

The following are common forms of flux/slope limiter function, $\phi\ (r)$ :

CHARM [not 2nd order TVD] (Zhou, 1995)

$\phi_{cm}(r) = \frac{ r \left( 3 r + 1 \right)}{ \left( r+1 \right)^2} ; \quad \lim_{r \rightarrow \infty}\phi_{cm}(r) = 3$ .

HCUS [not 2nd order TVD] (Waterson & Deconinck, 1995)

$\phi_{hc}(r) = \frac{ 1.5 \left(r+\left| r \right| \right)}{ \left(r+2 \right)} ; \quad \lim_{r \rightarrow \infty}\phi_{hc}(r) = 3$ .

HQUICK [not 2nd order TVD] (Waterson & Deconinck, 1995)

$\phi_{hq}(r) = \frac{2 \left(r + \left|r \right| \right)}{ \left(r+3 \right)} ; \quad \lim_{r \rightarrow \infty}\phi_{hq}(r) = 4$ .

Koren (Koren, 1993)

$\phi_{kn}(r) = \max \left[ 0, \min \left(2 r, \left(1+2r \right)/3, 2 \right) \right]; \quad \lim_{r \rightarrow \infty}\phi_{kn}(r) = 2$ .

minmod - symmetric (Roe, 1986)

$\phi_{mm} (r) = \max \left[ 0 , \min \left( 1 , r \right) \right] ; \quad \lim_{r \rightarrow \infty}\phi_{mm}(r) = 1$ .

monotonized central (MC) - symmetric (van Leer, 1977)

$\phi_{mc} (r) = \max \left[ 0 , \min \left( 2 r, 0.5 (1+r), 2 \right) \right] ; \quad \lim_{r \rightarrow \infty}\phi_{mc}(r) = 2$ .

Osher (Chatkravathy and Osher, 1983)

$\phi_{os} (r) = \max \left[ 0 , \min \left( r, \beta \right) \right], \quad \left(1 \leq \beta \leq 2 \right) ; \quad \lim_{r \rightarrow \infty}\phi_{os} (r) = \beta$ . Stanley Osher (born 1942) is an American mathematician known for his many contributions in Shock capturing, Level set methods and PDE -based

ospre - symmetric (Waterson & Deconinck, 1995)

$\phi_{op} (r) = \frac{1.5 \left(r^2 + r \right) }{\left(r^2 + r +1 \right)} ; \quad \lim_{r \rightarrow \infty}\phi_{op} (r) = 1.5$ .

smart [not 2nd order TVD] (Gaskell & Lau, 1988)

$\phi_{sm}(r) = \max \left[ 0, \min \left(2 r, \left(0.25 + 0.75 r \right), 4 \right) \right] ; \quad \lim_{r \rightarrow \infty}\phi_{sm}(r) = 4$ .

superbee - symmetric (Roe, 1986)

$\phi_{sb} (r) = \max \left[ 0, \min \left( 2 r , 1 \right), \min \left( r, 2 \right) \right] ; \quad \lim_{r \rightarrow \infty}\phi_{sb} (r) = 2$ .

Sweby - symmetric (Sweby, 1984)

$\phi_{sw} (r) = \max \left[ 0 , \min \left( \beta r, 1 \right), \min \left( r, \beta \right) \right], \quad \left(1 \leq \beta \leq 2 \right) ; \quad \lim_{r \rightarrow \infty}\phi_{sw} (r) = \beta$ .

UMIST (Lien & Leschziner, 1994)

$\phi_{um}(r) = \max \left[ 0, \min \left(2 r, \left(0.25 + 0.75 r \right), \left(0.75 + 0.25 r \right), 2 \right) \right] ; \quad \lim_{r \rightarrow \infty}\phi_{um}(r) = 2$ .

van Albada 1 - symmetric (van Albada, et al, 1982)

$\phi_{va1} (r) = \frac{r^2 + r}{r^2 + 1 } ; \quad \lim_{r \rightarrow \infty}\phi_{va1} (r) = 1$ .

van Albada 2 Alternative form [not 2nd order TVD] used on high spatial order schemes (Kermani, 2003)

$\phi_{va2} (r) = \frac{2 r}{r^2 + 1} ; \quad \lim_{r \rightarrow \infty}\phi_{va2} (r) = 0$ .

van Leer - symmetric (van Leer, 1974)

$\phi_{vl} (r) = \frac{r + \left| r \right| }{1 + r } ; \quad \lim_{r \rightarrow \infty}\phi_{vl} (r) = 2$ . Bram van Leer is professor of aerospace engineering at the University of Michigan, in Ann Arbor.

All the above limiters indicated as being symmetric, exhibit the following symmetry property,

$\frac{ \phi \left( r \right)}{r} = \phi \left( \frac{1}{r} \right)$ .

This is a desirable property as it ensures that the limiting actions for forward and backward gradients operate in the same way.

Admissible limiter region for second-order TVD schemes.

Unless indicated to the contrary, the above limiter functions are second order TVD. In systems described by Partial differential equations such as the following hyperbolic Advection equation, \frac{\part u}{\part t} + a\frac{\part u}{\part This means that they are designed such that they pass through a certain region of the solution, known as the TVD region, in order to guarantee stability of the scheme. Second-order, TVD limiters satisfy at least the following criteria:

$r \le \phi(r) \le 2r, \left( 0 \le r \le 1 \right) \$ ,
$1 \le \phi(r) \le r, \left( 1 \le r \le 2 \right) \$ ,
$1 \le \phi(r) \le 2, \left( r > 2 \right) \$ ,
$\phi(1) = 1 \$ ,

The admissible limiter region for second-order TVD schemes is shown in the Sweby Diagram opposite (Sweby, 1984), and plots showing limiter functions overlaid onto the TVD region are shown below. In this image, plots for the Osher and Sweby limiters have been generated using $β = 1. 5$ .

Limiter functions overlaid onto second-order TVD region.

Generalised minmod limiter

An additional limiter that has an interesting form is the generalised minmod limiter (Harten and Osher, 1987). It is defined as follows

$\phi_{mg}(u,\theta)=\textrm{minmod}\left(\theta\frac{u_{i}-u_{i-1}}{\Delta x},\;\frac{u_{i+1}-u_{i-1}}{2\Delta x},\;\theta\frac{u_{i+1}-u_{i}}{\Delta x}\right),\quad\theta\in\left[1,2\right],$

where

$\textrm{minmod}\left(z_{1},z_{2},\cdots\right):=\left\{ \begin{array}{cc} \min_{j}\quad & \textrm{if}\quad z_{j}>0\quad \forall j\\ \max_{j\quad} & \textrm{if}\quad z_{j}<0\quad \forall j\\ 0 & \textrm{otherwise}\end{array}\right. .$

Note: $\phi_{mg} \$ is most dissipative for $\theta=1, \$ when it reduces to $\phi_{mm}, \$ and is least dissipative for $\theta=2 \$ .

References

Chakravarthy, S R and Osher, S, (1983), High resolution applications of the Osher upwind scheme for the Euler equations, AIAA Paper 83-1943, Proc. Godunov's theorem, also known as Godunov's order barrier theorem, is a mathematical Theorem important in the development of the theory of High resolution schemes High-resolution schemes are used in the numerical solution of Partial differential equations where high accuracy is required in the presence of shocks or discontinuities MUSCL stands for Monotone Upstream-centered Schemes for Conservation Laws, and the term was introduced in a seminal paper by Bram van Leer (van Leer 1979 Sergei Konstantinovich Godunov (b July 17, 1929 in Moscow, Russia) is professor at the Sobolev Institute of Mathematics of the In systems described by Partial differential equations such as the following hyperbolic Advection equation, \frac{\part u}{\part t} + a\frac{\part u}{\part AIAA 6th Computational Fluid Dynamics Conference, pp 363-73 (link).
Gaskell, P H and A K C Lau, (1988), Curvature-compensated convective transport: SMART, a new boundedness-preserving transport algorithm, Int. J. Num. Meth. Fluids, 8, p617.
Harten, A. and S. Osher, (1987). Uniformly high-order accurate nonoscillatory schemes. I, SIAM J. Numer. Anal. , 24, pp. 279–309.
Hirsch, C, (1990), Numerical Computation of Internal and External Flows, volume 2: Computational Methods for Inviscid and Viscous Flows, Wiley.
Kermani, M. J. , Gerber, A. G. , and Stockie, J. M. (2003), Thermodynamically Based Moisture Prediction Using Roe’s Scheme, 4th Conference of Iranian AeroSpace Society, Amir Kabir University of Technology, Tehran, Iran, January 27–29.
Koren, B, (1993), A robust upwind discretisation method for advection, diffusion and source terms, In: Numerical Methods for Advection-Diffusion Problems, Ed. C. B. Vreugdenhil & B. Koren, Vieweg, Braunschweig, p117.
Leonard, B P, M A Leschziner and J McGuirk, (1978), The QUICK algorithm: a uniformly 3rd-order finite-difference method for highly convective flows, Proc. 1st Conf. on Numerical Methods in Laminar & Turbulent Flow, Swansea, p807.
Lien, F S, and M. A. Leschziner, (1994), Upstream monotonic interpolation for scalar transport with application to complex turbulent flows, Int. J. Num. Meth. Fluids, 19, p527.
Roe, P L, (1986), Characteristic-based schemes for the Euler equations, Ann. Rev. Fluid Mech. , 18, p337.
Sweby, P K, (1984), High resolution schemes using flux-limiters for hyperbolic conservation laws. SIAM J. Num. Anal. , 21, p995-1011.
Van Albada, G D, B. Van Leer and W. W. Roberts, (1982), A comparative study of computational methods in cosmic gas dynamics, Astron. Astrophysics, 108, p76.
Van Leer, B, (1974), Towards the ultimate conservative difference scheme II. Monotonicity and conservation combined in a second order scheme. J. Comp. Phys. , 14, p361-70.
Van Leer, B, (1977), Towards the ultimate conservative difference scheme III. Upstream-centered finite-difference schemes for ideal compressible flow. , J. Comp. Phys. , 23, p263-75.
Van Leer, B, (1979), Towards the ultimate conservative difference scheme V, J. Comp. Phys. , 32, p101.
Waterson, N P and H Deconinck, (1995), A unified approach to the design and application of bounded higher-order convection schemes, VKI Preprint 1995-21.
Zhou, G, (1995), Numerical simulations of physical discontinuities in single and multi-fluid flows for arbitrary Mach numbers, PhD Thesis, Chalmers Univ. of Tech. , Goteborg, Sweden.

Contents

How they work

Limiter functions

Generalised minmod limiter

See also

References

Further reading