GCM for liquid fuel properties in spray

[d-montgomery]

This PR builds on the reorganization work done in #581, #602, and #613, and introduces a new group-contribution method (GCM) for estimating liquid-phase properties in the spray module. This method has been shown to be effective at estimating thermodynamic properties of multi-component jet fuels with limited information about the specific compounds in the fuel. Using the GCM in Pele requires:

• setting SPRAY_GCM=TRUE in the GNUmakefile of the associated PeleLMeX case directory
• generating an additional liquid-fuel-specific input file from FuelLib following this tutorial provided in that repo's documentation

To minimize headaches from unit conversions, the GCM method is currently only compatible with PeleLMeX, but it can be adapted for cgs units in the future. I've tested the implementation in PeleLMeX/Exec/RegTests/SingleDropEvap and plan to conduct additional tests with POSF10264 in the future. Here is a corresponding LMeX PR where all test cases can be run PeleLMeX #561

Below are the initial results. I think where this method will shine is dealing with complex multi-component fuels like POSF10264, where current mechanisms only have one liquid-phase species and are unable to capture preferential evaporation.

Note: The initial increase in droplet diameter is due to the decrease in liquid density with increasing temperature. Eventually, the droplet starts losing mass and hence leads to a decrease in droplet diameter.

[Copilot]

Pull Request Overview

This PR introduces a Group Contribution Method (GCM) for estimating liquid-phase properties in the spray module, building on previous reorganization work and providing an alternative to the original PeleMP approach. The GCM uses correlations based on molecular structure information to predict thermodynamic properties of multi-component jet fuels.

Key changes:

• Adds GCM implementation with temperature-dependent correlations for liquid properties
• Restructures liquid property classes with inheritance hierarchy
• Consolidates unit conversion utilities and spray units definition
• Updates documentation to cover both PeleMP and GCM approaches

Reviewed Changes

Copilot reviewed 8 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
UnitConversions.H	Adds temperature conversion functions (Celsius to Kelvin)
SpraySetup.cpp	Reorganizes liquid property initialization and adds molecular weight handling
SprayProperties.H	Major refactor adding GCM implementation, base class hierarchy, and consolidated unit definitions
SprayFuelData.H	Removes duplicate unit definitions (moved to SprayProperties.H)
Drag.H	Updates to use liquid molecular weights and simplified vapor state calculations
WallFilm.H	Simplifies molecular weight calculation using new mixture functions
Spray.rst	Comprehensive documentation update covering both property estimation methods
CONTRIBUTING.md	Minor formatting improvements with code block syntax

Comments suppressed due to low confidence (1)

Source/Spray/SprayProperties.H:1

• The input parameter name 'SP_accentric_factor' in the documentation (line 426) has a spelling error. It should be 'acentric' not 'accentric'.

#ifndef SPRAYPROPERTIES_H

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