• equilibrium temperature
• high temperature
• plastic hinge
• thermo-mechanical analysis
• thermal analysis
• radiation cooling
• film cooling
• adiabatic wall temperature
• film coefficient
• convection
• nozzle extension
• combustion chamber
• thrust chamber
• rocket engine

A 2D thermo–mechanical model for small bipropellant rocket thrust chambers is developed with the aim of a first attempt estimation of thermal and structural responses. The model neglects the injection plate and only focuses on the first engine run, from the ignition to the steady state regime. No significant limitations on nodes and elements number are present, due to the axial symmetry of the system.
Convection loads are firstly estimated by the Bartz’s correlation, then a film cooling model is developed in order to include the film cooling effect. Radiation is modeled for the external surface (radiation cooling) and for the internal one, considering the presence of a participating medium. All the simulation input are discretized, dividing the thrust chamber in stations. A sensitivity study shows that a large number of stations should be used in describing the first operating instants.
The ANSYS software is used for the transient thermo–mechanical simulation. Results show that the most heated region is near the throat and high thermal gradients in the first instants produce compression and traction regions. Moreover, the importance of cooling techniques is emphasized: on average, radiation cooling reduce the wall temperature of the combustion chamber up to 20%, while film cooling up to 60−70%. By applying the thermal model to the R-4D rocket engine, a comparison of thermal results with temperature test data shows that the model can predict good results before the throat, but quite high relative errors are observed in the diverging nozzle. Thermo–structural results show that the structure soon reaches local plasticity conditions, with very small deformations. The critical locations, both on stress and strain levels, are the converging–diverging nozzle, especially the throat, and the chamber region near the nozzle extension interface.
Finally, the present model is applied to a new rocket engine, currently under development at University of Pisa in the project “400 Newton Green Bipropellant Rocket Engine”.
The main limits and capabilities of the themo–mechanical model are highlighted and commented.