Computational investigation of cooling effectiveness for film cooled dual-bell exhaust nozzle for LO2/LH2 liquid rocket engines

Abstract

ABSTRACT A dual bell nozzle (DBN) consists of two bell nozzles of different geometric area ratios attached at the region called inflection. This distinct geometry modification allows the nozzle to adapt to altitudes through its different operating modes. A numerical investigation with hot flow is done on a 2-dimensional axisymmetric model of a DBN having coolant injection at its inflection. Analysis has considered the secondary injection of gaseous hydrogen film into the gas mixture resulting from the combustion of liquid hydrogen and liquid oxygen in the thrust chamber of a LO2/LH2 engine. Model gave a root mean square deviation of 0.0012 from the experimental result at 30 NPR. Flow phenomena inside the nozzle are studied for different altitudes with and without coolant injection. Shift of separation location inside the nozzle on changing the quantity of gaseous hydrogen injected for three nozzle pressure ratios in the range of operation of the nozzle is calculated. The nondimensional shift in separation location is estimated to be 1.34 at 30 NPR, 1.10 at 45 NPR and 0.70 at 60 NPR. Temperature distribution on nozzle wall and cooling effectiveness of coolant on nozzle wall is determined with varying coolant mass flow rate for LO2/LH2 and LO2/RP1 rocket engines and the results are compared. The effectiveness of coolant for LO2/LH2 engine reduces from 1 to 0.78 on moving downstream of the nozzle whereas it reduces from 1 to 0.27 for LO2/RP1 engine. The study also predicts reduction in specific impulse of 5% for LO2/LH2 engine and 3.3% for the LO2/RP1 engine at MR = 15 due to the film cooling.