Entry 02 // Propulsion
Multi-System Propulsion CFD Analysis
Numerical analysis of three propulsion systems in ANSYS Fluent: a ramjet, a chemical rocket, and a resistojet, looking at the flow physics that governs thrust in each cycle across 15 cases.
1.0 Overview
Each engine was modeled with simplified two-dimensional geometries informed by established propulsion literature and verified through a mesh-independence study across five mesh densities. The simulations explored how fuel choice, mixture ratio, geometric design, and operating conditions influence propulsive efficiency.
The point of running all three cycles rather than one was comparative: a ramjet, a chemical rocket, and a resistojet generate thrust by different mechanisms, so validating one modeling approach across all three is a stronger check than tuning a single case until it matches.
2.0 Modeling approach
- Geometry built from classical propulsion literature
- Mesh-independence study across five mesh densities
- Pressure-based steady solver with the energy equation enabled
- Species transport with a finite-rate / eddy-dissipation combustion model
- k-ω SST turbulence model for near-wall accuracy
Fluent output was converted to performance metrics using the classical relations:
T = ṁVe + (pe − pa)Ae
Isp = T / (ṁg₀)
TSFC = ṁfuel / T
CF = F / (ptAt)
3.0 Ramjet
Simulated at flight Mach numbers of 1.5, 2.0, and 3.0 with methane and hydrogen fuels at two fuel-to-air ratios, to assess how inlet compression, combustion behavior, and mixing affect thrust, specific impulse, and TSFC.
| Case | Mach | Fuel | F/A | Thrust (N) | TSFC (kg/N·s) | Isp (s) |
|---|---|---|---|---|---|---|
| 1 | 1.5 | H₂ | 0.05 | 28,422 | 1.26×10⁻⁴ | 580 |
| 2 | 2.0 | CH₄ | 0.20 | 54,835 | 3.85×10⁻⁴ | 279 |
| 3 | 2.0 | H₂ | 0.05 | 48,261 | 1.04×10⁻⁴ | 984 |
| 4 | 3.0 | CH₄ | 0.20 | 117,854 | 1.70×10⁻⁴ | 601 |
| 5 | 3.0 | H₂ | 0.05 | 122,211 | 4.03×10⁻⁵ | 2,492 |
Ramjet findings
- Hydrogen at Mach 3 produced the highest thrust and specific impulse, from better combustion efficiency and lighter exhaust products
- Thrust rose sharply from Mach 2 to Mach 3, with the hydrogen case exceeding 122 kN
- Hydrogen gave much higher Isp (up to 2,492 s) and lower TSFC than methane
- Methane cases showed pockets of unburned fuel at high fuel-air ratios, meaning incomplete combustion
- At Mach 3, inlet shocks caused excessive stagnation pressure loss, which is the price of the thrust gain
4.0 Chemical rocket
Evaluated across two propellants, two mixture ratios, and two chamber lengths, isolating the effect of chamber pressure, nozzle expansion, and propellant chemistry on efficiency.
| Case | CR1 | CR2 | CR3 | CR4 | CR5 | CR6 |
|---|---|---|---|---|---|---|
| Isp (s) | 98.5 | 121.2 | 88.1 | 19.9 | 99.5 | 47.4 |
TSFC and thrust coefficient are not reported for the rocket cases: fuel-only mass flow and throat area were not logged, so neither can be computed from the recorded data.
Chemical rocket findings
- Longer chambers gave more complete methane combustion and higher exit velocity
- Hydrogen cases produced very high chamber pressures and high efficiency under lean conditions
- Lean hydrogen in the 5 m chamber (CR2, 121.2 s) was the best case
- Over-rich hydrogen (CR4, 19.9 s) performed worst. Raising mixture ratio buys thrust but costs Isp once combustion goes fuel-rich
5.0 Resistojet
Explored how inlet velocity, electric heating strength, and micro-nozzle geometry affect the thermally driven exhaust acceleration characteristic of electric propulsion.
Resistojet findings
- Higher inlet velocity increased mass flow and therefore thrust
- Stronger electric fields raised heater power and exit temperature, improving exhaust velocity
- Electrical energy input is the dominant driver of specific impulse
- Increasing heater power delivered disproportionately large Isp gains
Full report
Geometry, mesh study, solver setup, and the complete case matrix for all three cycles.