Coupled Flow-Thermal Analysis of a Rocket Nozzle with Charring Ablative Thermal Protection System

TL;DR

We address the challenge of predicting thermal and ablative response of a rocket nozzle protected by charring AVCOAT TPS under high-temperature flow. A conjugate flow–thermal framework couples a commercial CFD solver (ANSYS Fluent) with an in-house transient material solver (CATS) through a non-iterative exchange of wall boundary conditions, incorporating a Kays blowing correction to model pyrolysis-gas effects. The flow solver is validated against the NASA Back et al. Case 262, and the material-response model is validated in prior work, establishing confidence in coupled predictions. Results identify the nozzle throat as the most thermally critical region, with a maximum surface recession of about $2.5$ mm after $t = 120$ s and an ablation temperature of $T_{\text{abl}} = 922$ K, providing a robust framework for TPS design optimization in extreme nozzle environments.

Abstract

This paper presents a conjugate flow-thermal analysis of a rocket nozzle protected by a charring ablative thermal protection system (TPS). The study employs a coupled approach, integrating a CFD solver with an in-house transient material response code through the exchange of boundary conditions at the fluid-solid interface. The nozzle incorporates an AVCOAT TPS and is subjected to high-temperature compressible flow. Results identify the nozzle throat as the critical location, exhibiting the highest convective loading, early attainment of the material ablation temperature, and progressive surface recession. Temporal analysis of the coupled simulations reveals an initial peak in wall heat flux followed by a transient reduction and a subsequent resurgence as viscous dissipation and evolving surface conditions modify the near-wall thermal field. At 120 s of simulated operation, the maximum surface recession at the throat is approximately 2.5 mm. This research provides a methodology for predicting the thermal and ablative response of rocket nozzles equipped with charring TPS materials. The proposed framework offers valuable insights into the design and optimization of high-performance nozzles for extreme environments.

Figures (21)

• Figure 1: Nozzle with cooling duct mesh
• Figure 2: Grid independence and near-wall resolution assessment for the nozzle flow simulations.
• Figure 3: Heat transfer coefficient using different turbulence models
• Figure 4: Mach Number Variation.
• Figure 5: Temperature variation