APPLICATION OF AN INVERSE METHOD FOR THE ESTIMATION OF HEAT FLUX IN LOW-THRUST HYBRID PROPELLANT ROCKET MOTOR AND ITS ANALYTICAL VALIDATION
Ana Paula Castro de Paula Nunes1; Gabriel Pacheco Milhomem1; Vinicius Carvalho Rispoli1; Artem Andrianov1
1 Universidade de Brasilia
doi:10.20906/CPS/CILAMCE2017-0107
Resumo
The presented study was motivated by the necessity to increase burning time of low-thrust hybrid test-motor that initially had been designed to operate on high regression rate propellant pair (paraffin and nitrous oxide) for 12 seconds. The substitution of paraffin for a polyethylene grain with the same geometry increases the operation time of motor up to 40-50 seconds. For this operation time, it is required the application of thermal protection in the combustion chamber. The main purpose of the study was to evaluate the heat insulator efficiency by determination of temperature on its external surface at the given conditions of motor's operation with increased burning time. To avoid direct temperature measurements for long time operation of motor an inverse heat conduction method was introduced in methodology of the study. It included test measurements of temperature on external surface of heat insulator for short-time operation of hybrid propellant test-motor. Experimental temperature data, presented on a temperature-time plot, were used to determine heat flux boundary condition at internal surface of insulator's wall with known thermal properties by finite-element method (commercial software Ansys Workbench). The values of heat flux were then validated through the analytical solution of a heat equation problem on cylindrical domain. Solution was obtained using an integral transform approach, where the transform kernel was based on the solution of an associated Sturm-Liouville boundary value problem. Then, validated values of heat flux were used to predict temperature on external surface of heat insulator for increased operation time of the test-motor. The given methodology made possible the evaluation of temperatures on external surface of cylindrical heat insulator fabricated from cotton fabric reinforced phenolic composite. Short-time (10 seconds) experimental temperature measurements together with low oxidizer-to-fuel ratio excluded any thermal deterioration of structural casing of the test-motor. The m
Palavras-chave: heat conduction; heat transfer; inverse method; heat equation; hybrid rocket; rocket motor; internal insulator; integral transform; analytical; numerical