MultiSpeciesEuler: add module

doc/headers/modules.h

@@ -85,6 +85,14 @@
  */
 
 
+/**
+ * @defgroup MultiSpeciesEulerEquations The Multi-Species Euler Equations
+ *
+ * This module contains classes and functions related to solving the
+ * multi-species compressible Euler equations with ideal gas mixtures.
+ */
+
+
 /**
  * @defgroup SkeletonEquations Minimal equation interface
  *

doc/references.bib

@@ -24,6 +24,13 @@ @article{Brooks1982
   doi     = {10.1016/0045-7825(82)90071-8}
 }
 
+@article{ClaytonDzanicTovar-2025,
+  author = {Bennett Clayton and Tarik Dzanic and Eric Tovar},
+  title = {Invariant-domain preserving high-order time stepping for multi-species ideal gas mixtures},
+  year = {2025},
+  journal = {submitted}
+}
+
 @article{Chertock2015,
   author     = {Chertock, A. and Cui, S. and Kurganov, A. and Wu, T.},
   title      = {Well-balanced positivity preserving central-upwind scheme for

source/multi_euler_ideal/CMakeLists.txt

@@ -0,0 +1,17 @@
+##
+## SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+## Copyright (C) 2023 - 2025 by the ryujin authors
+## Copyright (C) 2025 by Triad National Security, LLC
+##
+
+add_library(obj_multi_euler_ideal OBJECT
+  equation_dispatch.cc
+  initial_state_library.cc
+  limiter.cc
+  riemann_solver.cc
+  )
+set_target_properties(obj_multi_euler_ideal PROPERTIES LINKER_LANGUAGE CXX)
+deal_ii_setup_target(obj_multi_euler_ideal)
+target_link_libraries(obj_multi_euler_ideal obj_common ${EXTERNAL_TARGETS})
+# Propagate the current source directory with PUBLIC visibility
+target_include_directories(obj_multi_euler_ideal PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

source/multi_euler_ideal/description.h

@@ -0,0 +1,84 @@
+//
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// Copyright (C) 2023 - 2025 by the ryujin authors
+// Copyright (C) 2025 by Triad National Security, LLC
+//
+
+#pragma once
+
+#include <compile_time_options.h>
+
+#include "../stub_parabolic_module.h"
+#include "../stub_parabolic_system.h"
+#include "hyperbolic_system.h"
+#include "indicator.h"
+#include "limiter.h"
+#include "riemann_solver.h"
+
+namespace ryujin
+{
+  namespace MultiSpeciesEuler
+  {
+    /**
+     * A struct that contains all equation specific classes describing the
+     * chosen hyperbolic system, the indicator, the limiter and
+     * (approximate) Riemann solver.
+     *
+     * The compressible multi-species Euler equations of gas dynamics for
+     * an ideal gas mixture under the assumption of thermal-mechanical
+     * equilibrium. Each species \f$k\f$ is modeled by an ideal gas with
+     * specific heat capacities \f$c_{p,k}\f$ and \f$c_{v,k}\f$.
+     *
+     * The governing equations are:
+     * \f{align}
+     *   \partial_t (\alpha_k \rho_k) + \nabla \cdot (\alpha_k \rho_k
+     *   \mathbf{v}) &= 0, \quad k = 1, \ldots, n_s, \\
+     *   \partial_t \mathbf{m} + \nabla \cdot (\mathbf{v} \otimes \mathbf{m}
+     *   + p \mathbb{I}_d) &= 0, \\
+     *   \partial_t E + \nabla \cdot ((E + p) \mathbf{v}) &= 0,
+     * \f}
+     * where \f$\alpha_k \rho_k\f$ are the partial densities, \f$\mathbf{m}
+     * = \rho \mathbf{v}\f$ is the mixture momentum, \f$E\f$ is the mixture
+     * total energy, and \f$p\f$ is the mixture pressure. The mixture
+     * pressure is given by \f$p = (\bar{\gamma} - 1) \varepsilon\f$ where
+     * \f$\bar{\gamma} = \bar{c}_p / \bar{c}_v\f$ is the mixture ratio of
+     * specific heats.
+     *
+     * The numerical scheme ensures preservation of an invariant domain
+     * \f$\mathcal{A} = \{ \mathbf{u} : \alpha_k \rho_k \geq 0,\;
+     * \varepsilon(\mathbf{u}) > 0,\; s(\mathbf{u}) \geq s_{\min} \}\f$,
+     * where \f$s(\mathbf{u})\f$ is the mixture specific entropy.
+     *
+     * The parabolic subsystem is chosen to be the identity (inviscid flow).
+     *
+     * @note See "Second-order invariant-domain preserving approximation to
+     * the multi-species Euler equations" by Clayton, Dzanic, and Tovar
+     * (arXiv:2505.09581) for full details of the mathematical formulation
+     * and numerical scheme.
+     *
+     * @ingroup MultiSpeciesEulerEquations
+     */
+    struct Description {
+      using HyperbolicSystem = MultiSpeciesEuler::HyperbolicSystem;
+
+      template <int dim, typename Number = double>
+      using HyperbolicSystemView =
+          MultiSpeciesEuler::HyperbolicSystemView<dim, Number>;
+
+      using ParabolicSystem = ryujin::StubParabolicSystem;
+
+      template <int dim, typename Number = double>
+      using ParabolicModule =
+          ryujin::StubParabolicModule<Description, dim, Number>;
+
+      template <int dim, typename Number = double>
+      using Indicator = MultiSpeciesEuler::Indicator<dim, Number>;
+
+      template <int dim, typename Number = double>
+      using Limiter = MultiSpeciesEuler::Limiter<dim, Number>;
+
+      template <int dim, typename Number = double>
+      using RiemannSolver = MultiSpeciesEuler::RiemannSolver<dim, Number>;
+    };
+  } // namespace MultiSpeciesEuler
+} // namespace ryujin

source/multi_euler_ideal/equation_dispatch.cc

@@ -0,0 +1,18 @@
+//
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// Copyright (C) 2024 - 2025 by the ryujin authors
+// Copyright (C) 2025 by Triad National Security, LLC
+//
+
+#include "description.h"
+
+#include <compile_time_options.h>
+#include <equation_dispatch.h>
+
+namespace ryujin
+{
+  namespace MultiSpeciesEuler
+  {
+    Dispatch<Description, NUMBER> dispatch_instance("multi species euler");
+  } // namespace MultiSpeciesEuler
+} // namespace ryujin