SpECTRE  v2021.10.04
NewtonianEuler::Solutions::RiemannProblem< Dim > Class Template Reference

Analytic solution to the Riemann Problem. More...

#include <RiemannProblem.hpp>

## Classes

The adiabatic index of the fluid. More...

struct  InitialData
Holds initial data on a side of the discontinuity and related quantities. More...

struct  InitialPosition
Initial position of the discontinuity. More...

struct  LeftMassDensity
The mass density on the left of the initial discontinuity. More...

struct  LeftPressure
The pressure on the left of the initial discontinuity. More...

struct  LeftVelocity
The velocity on the left of the initial discontinuity. More...

struct  PressureStarTol
The tolerance for solving for $$p_*$$. More...

struct  RightMassDensity
The mass density on the right of the initial discontinuity. More...

struct  RightPressure
The pressure on the right of the initial discontinuity. More...

struct  RightVelocity
The velocity on the right of the initial discontinuity. More...

## Public Types

using equation_of_state_type = EquationsOfState::IdealFluid< false >

using source_term_type = Sources::NoSource

using options = tmpl::list< AdiabaticIndex, InitialPosition, LeftMassDensity, LeftVelocity, LeftPressure, RightMassDensity, RightVelocity, RightPressure, PressureStarTol >

## Public Member Functions

RiemannProblem (const RiemannProblem &)=delete

RiemannProblemoperator= (const RiemannProblem &)=delete

RiemannProblem (RiemannProblem &&)=default

RiemannProblemoperator= (RiemannProblem &&)=default

RiemannProblem (double adiabatic_index, double initial_position, double left_mass_density, const std::array< double, Dim > &left_velocity, double left_pressure, double right_mass_density, const std::array< double, Dim > &right_velocity, double right_pressure, double pressure_star_tol=PressureStarTol::suggested_value())

template<typename DataType , typename... Tags>
tuples::TaggedTuple< Tags... > variables (const tnsr::I< DataType, Dim, Frame::Inertial > &x, double t, tmpl::list< Tags... >) const
Retrieve a collection of hydrodynamic variables at position x and time t

const EquationsOfState::IdealFluid< false > & equation_of_state () const

void pup (PUP::er &)

constexpr std::array< double, 2 > diagnostic_star_region_values () const

## Static Public Attributes

static constexpr Options::String help

## Friends

template<size_t SpatialDim>
bool operator== (const RiemannProblem< SpatialDim > &lhs, const RiemannProblem< SpatialDim > &rhs)

## Detailed Description

template<size_t Dim>
class NewtonianEuler::Solutions::RiemannProblem< Dim >

Analytic solution to the Riemann Problem.

This class implements the exact Riemann solver described in detail in Chapter 4 of . We follow the notation there. The algorithm implemented here allows for 1, 2 and 3D wave propagation along any coordinate axis. Typical initial data for test cases (see ) include:

• Sod's Shock Tube (shock on the right, rarefaction on the left):
• $$(\rho_L, u_L, p_L) = (1.0, 0.0, 1.0)$$
• $$(\rho_R, u_R, p_R) = (0.125, 0.0, 0.1)$$
• Recommended setup for sample run:
• InitialTimeStep: 0.0001
• Final time: 0.2
• DomainCreator along wave propagation (no AMR):
• Interval of length 1
• InitialRefinement: 8
• InitialGridPoints: 2
• "123" problem (two symmetric rarefaction waves):
• $$(\rho_L, u_L, p_L) = (1.0, -2.0, 0.4)$$
• $$(\rho_R, u_R, p_R) = (1.0, 2.0, 0.4)$$
• Recommended setup for sample run:
• InitialTimeStep: 0.0001
• Final time: 0.15
• DomainCreator along wave propagation (no AMR):
• Interval of length 1
• InitialRefinement: 8
• InitialGridPoints: 2
• Collision of two blast waves (this test is challenging):
• $$(\rho_L, u_L, p_L) = (5.99924, 19.5975, 460.894)$$
• $$(\rho_R, u_R, p_R) = (5.99242, -6.19633, 46.0950)$$
• Recommended setup for sample run:
• InitialTimeStep: 0.00001
• Final time: 0.012
• DomainCreator along wave propagation (no AMR):
• Interval of length 1
• InitialRefinement: 8
• InitialGridPoints: 2
• Lax problem:
• $$(\rho_L, u_L, p_L) = (0.445, 0.698, 3.528)$$
• $$(\rho_R, u_R, p_R) = (0.5, 0.0, 0.571)$$
• Recommended setup for sample run:
• InitialTimeStep: 0.00001
• Final time: 0.1
• DomainCreator along wave propagation (no AMR):
• Interval of length 1
• InitialRefinement: 8
• InitialGridPoints: 2

where $$\rho$$ is the mass density, $$p$$ is the pressure, and $$u$$ denotes the normal velocity.

Note
Currently the propagation axis must be hard-coded as a size_t private member variable propagation_axis_, which can take one of the three values PropagationAxis::X, PropagationAxis::Y, and PropagationAxis::Z.

### Details

The algorithm makes use of the following recipe:

• Given the initial data on both sides of the initial interface of the discontinuity (here called "left" and "right" sides, where a coordinate axis points from left to right), we compute the pressure, $$p_*$$, and the normal velocity, $$u_*$$, in the so-called star region. This is done in the constructor. Here "normal" refers to the normal direction to the initial interface.
• Given the pressure and the normal velocity in the star region, two Wave structs are created, which represent the waves propagating at later times on each side of the contact discontinuity. Each Wave is equipped with two structs named Shock and Rarefaction which contain functions that compute the primitive variables depending on whether the wave is a shock or a rarefaction.
• If $$p_* > p_K$$, the wave is a shock, otherwise the wave is a rarefaction. Here $$K$$ stands for $$L$$ or $$R$$: the left and right initial pressure, respectively. Since this comparison can't be performed at compile time, each Wave holds a bool member is_shock_ which is true if it is a shock, and false if it is a rarefaction wave. This variable is used to evaluate the correct functions at run time.
• In order to obtain the primitives at a certain time and spatial location, we evaluate whether the spatial location is on the left of the propagating contact discontinuity $$(x < u_* t)$$ or on the right $$(x > u_* t)$$, and we use the corresponding functions for left or right Waves, respectively.
Note
The characterization of each propagating wave will only depend on the normal velocity, while the initial jump in the components of the velocity transverse to the wave propagation will be advected at the speed of the contact discontinuity ( $$u_*$$).

## ◆ help

template<size_t Dim>
 constexpr Options::String NewtonianEuler::Solutions::RiemannProblem< Dim >::help
staticconstexpr
Initial value:
= {
"Riemann Problem in 1, 2 or 3D along any coordinate axis."}

The documentation for this class was generated from the following files:
• src/Evolution/Executables/NewtonianEuler/EvolveNewtonianEulerFwd.hpp
• src/PointwiseFunctions/AnalyticSolutions/NewtonianEuler/RiemannProblem.hpp