Structural Optimization of Regeneratively Cooled Rotating Detonation Rocket Engines

Abstract

Combustors in rotating detonation rocket engines (RDREs) must withstand prolonged exposure to high heat fluxes (>10 MW/m2 ) and ultrasonic-frequency detonative loading. Regenerative cooling is being considered for thermal management in RDREs, but there is concern that the cooling channels may fail by fatigue due to the detonative loads. In the present work a structural optimization protocol for regeneratively cooled RDREs is developed and then used to determine optimal cooling channel geometries which minimize thermomechanical stresses that might drive such failures. The analysis considers thermal stresses from temperature gradients through the combustor wall, bending stresses due to cooling channel pressurization, and dynamic stresses from detonative loading. To calculate the dynamic stresses, the combustor hot wall is approximated as a beam on an elastic foundation, where the stiffness of the elastic foundation is a function of the cooling channel geometry and the properties of the combustor material. The structural optimization framework is applied to an exemplary RP2/GOX RDRE combustor, and optimal designs are determined as a function of propellant flow rate for several candidate combustor materials – GRCop-84, IN718, W-25Re, Nb-C103. The deviatoric stress in the hot wall increases monotonically with propellant flow rate. In all cases onset of yielding limits the maximum achievable flow rate. W-25Re can achieve the highest propellant flow rate of the materials considered here, owing to its combination of high thermal conductivity and high strength at elevated temperatures. While thermal stresses dominate most of the design space for each material, dynamic stresses become significant when the detonation wave speed approaches the elastic wave speed of the hot wall. This effect is important in Nb-C103, GRCop-84, and W25Re combustors, since the detonation wave speed matches the elastic wave speed for cooling channel designs that minimize static stresses. These results highlight the importance of dynamic stresses in regeneratively cooled RDREs, as combustor designs which minimize static stresses can sometimes amplify dynamic stresses, mitigating creep but promoting fatigue.