Meco Simulation Model and Component Graph

The Meco Rocket Simulator represents complex rocket engine systems through an interconnected component graph that models both liquid propellant flows and gas dynamics. This document explains how the simulation model works and how the component graph captures the physical relationships between different parts of the rocket engine system.

For a detailed overview of all available components, see the Components Reference page.

Model Architecture Overview

The simulation model is built around a **directed graph topology** where:

Nodes represent physical junction points and boundary conditions in the system
Branches represent flow paths connecting nodes (pipes, ducts, valves)
Components represent active elements that add or extract energy (pumps, turbines)
Control Parameters provide dynamic system control and time-varying inputs

This graph-based approach allows the simulator to model complex flow networks with multiple interconnected paths, branching flows, and coupled subsystems.

Dual Flow Network Architecture

The simulation model handles two distinct but interconnected flow networks:

Liquid Flow Networks

The liquid flow network models incompressible fluid flow through the propellant feed system:

Network Topology:

Liquid nodes serve as connection points and boundary conditions
Branches model pipes, cooling channels, and valves with viscous flow effects
Flow is governed by mass conservation and momentum equations
Pressure-driven flow with friction and fitting losses

Physical Modeling:

Turbulent and laminar flow regimes based on Reynolds numbers
Complex duct geometries (circular, rectangular, annular)
Multiple parallel cooling channels with volume factors
Pump work addition through machinery components

Key Components:

NodeInlet/NodeOutlet: Boundary conditions with controlled pressures
NodeInternal: Internal junction points with pressure dynamics
Branch: Flow connections with friction models and fitting losses
MachineryPump: Centrifugal pumps adding energy to liquid flow

Gas Flow Networks

The gas flow network models compressible flow through the combustion and exhaust systems:

Network Topology:

Gas nodes handle internal junctions and boundary conditions
Gas branches model high-speed compressible flow with choking effects
Flow governed by conservation of mass, momentum, and energy
Isentropic flow relations with friction and heat transfer

Physical Modeling:

Subsonic and supersonic flow regimes with Mach number tracking
Critical flow conditions and sonic choking at throats
Fanno flow with friction effects in ducts
Temperature and pressure ratio calculations

Key Components:

NodeGasInternal: Internal gas junctions with pressure dynamics
NodeGasGenerator: Combustion chambers mixing oxidizer and fuel
BranchGas: Compressible flow connections with Mach number evolution
MachineryTurbine: Gas turbines extracting energy from hot gas flow

Network Interaction and Coupling

The liquid and gas networks interact through several critical coupling mechanisms:

Combustion Coupling

The NodeGasGenerator serves as the primary coupling point between liquid and gas networks:

Liquid Inputs: Separate oxidizer and fuel liquid streams enter the gas generator
Mixing and Combustion: Liquid propellants mix and combust according to equilibrium chemistry
Gas Output: High-temperature, high-pressure combustion products exit as gas flow
Property Calculation: Gas properties (temperature, density, specific heat ratio) computed from oxidizer-fuel ratio and pressure

Heat Transfer Coupling

Solid components provide thermal coupling between gas and liquid networks:

Gas-Side Heat Transfer: Hot combustion gases transfer heat to chamber walls
Liquid-Side Cooling: Cold liquid propellant flows through cooling channels
Thermal Conduction: Heat conducts through solid material between gas and liquid sides
Regenerative Cooling: Liquid propellant preheated before injection, improving performance

Control System Coupling

Dynamic control parameters coordinate between networks:

Valve Control: Coordinated liquid and gas valve positions
Pressure Control: Boundary pressure control affecting both networks
Turbopump Coupling: Gas turbine drives liquid pumps through shaft connections

Fluid Property Propagation

The simulation uses a sophisticated fluid inheritance system to maintain consistent properties throughout each network:

Liquid Property Inheritance

Boundary Definition: Liquid properties defined at inlet boundary nodes
Forward Propagation: Properties inherited downstream through branches and nodes
Molecular Identity: Each liquid stream maintains its molecular identity (O2, H2, etc.)
Temperature Evolution: Liquid temperature changes due to pumping and heat transfer

Gas Property Evolution

Combustion Products: Gas properties calculated from chemical equilibrium
Dynamic Properties: Temperature, pressure, and composition evolve through network
Isentropic Relations: Property changes follow thermodynamic relations
Flow-Dependent Properties: Mach number and flow regime affect local properties

Network Solving Strategy

The simulation employs different numerical strategies for each network type:

Liquid Network Solution

Differential Equations: Mass conservation and momentum balance equations
Pressure Dynamics: Node pressures evolve based on mass flow imbalances
Friction Modeling: Darcy-Weisbach friction with automatic Reynolds number calculation
Pump Modeling: Performance curves relating head rise to flow rate

Gas Network Solution

Iterative Solution: Mass flow and pressure distribution solved iteratively
Finite Difference: Jacobian matrix computed using finite differences
Mach Number Tracking: Flow regime detection and sonic choking handling
Energy Balance: Temperature mixing at junction points

Component Graph Benefits

The component graph representation provides several key advantages:

Modularity

Components can be easily added, removed, or modified
Complex systems built from simple, well-understood elements
Reusable component library for different engine configurations

Physical Intuition

Graph structure mirrors actual physical connections
Engineers can visualize and understand system topology
Debugging and validation easier with clear component relationships

Scalability

Networks can range from simple test cases to full engine systems
Multiple engines or stages can be represented in single model
Component count limited only by computational resources

Flexibility

Different component types can be connected as needed
Control systems easily integrated throughout the model
New component types can be added without changing core infrastructure

Advanced Network Features

Multiple Cooling Circuits

Parallel cooling channels with different flow rates
Series-parallel combinations for complex heat exchangers
Volume factors to account for channel count and geometry

Transmission Systems

Shaft connections between turbines and pumps
Gear ratios and rotational dynamics
Power transmission through multiple stages

Valve Control

Time-varying valve positions with smooth transitions
Coordinated valve sequences for engine startup and shutdown
Pressure relief and safety valve modeling

Boundary Condition Flexibility

Time-varying pressure and temperature boundary conditions
Mass flow rate specifications for complex operational profiles
Ambient condition variations for altitude simulations

Model Validation and Verification

The component graph approach enables comprehensive model validation:

Component-Level Testing

Individual components validated against analytical solutions
Benchmark cases for each component type
Parametric studies to verify physical behavior

Network-Level Validation

Simple network configurations compared to analytical solutions
Progressive complexity building from validated simple cases
Mass and energy conservation checks throughout solution process

System-Level Verification

Full engine models compared to test data
Transient behavior validation during startup and shutdown
Performance parameter correlation with experimental measurements