Nozzle Loss Research Articles

Chemical and nozzle flow losses in hypersonic ramjets

Chemical and nozzle flow losses in hypersonic ramjets

Exact kinetic and approximate nozzle recombination losses

Exact kinetic and approximate nozzle recombination losses

Nozzle contours for minimum particle-lag loss

The flow of a gas-particle mixture through a rocket nozzle is analyzed under the approximation that the particle slip velocity is small compared with the average mixture velocity, using one-dimensional gasdynamics, the Stokes drag law, and corresponding approximations for the heat transfer between solid and gas phase. The variational problem defining the pressure distribution giving the minimum impulse loss due to particle lag is formulated and solved for nozzles of prescribed mass flow, length, and of given exit pressure or area. The throat section of the optimum nozzle is considerably elongated and more gradual than that of the conventional nozzle. The velocity and temperature lags were much lower (about 1/3) in the throat region than those for the conventional nozzle. The impulse loss of the optimum nozzle was, however, reduced only about 30% below that of the conventional nozzle. It is concluded that contouring of the nozzle to improve gas-particle flow performance will result in only very modest gains. As a direct consequence, the impulse losses calculated herein for optimum nozzles can be used as a rough but convenient approximation for the impulse losses in conventional nozzles having the same area ratio or pressure ratio.

Thrust Characteristics of Underexpanded Nozzles

The thrust characteristics of underexpanded nozzles are investigated both analytically and experimentally. Nozzle losses are expressed in terms of velocity coefficients and this theory is found to agree wi th the experimental results. Two basic nozzles were tested, each having a 1 / 2 in . throat d iam and 15 deg exit semiangle cone. One nozzle had a s m o o t h surface of 20 microin. while the other had a rough surface of 300 microin. Area ratios from 6 to 1 were tested by machin ing the nozzle exit plane normal to the nozzle axis. High-pressure, low-temperature air was used as the working m e d i u m with a nozzle inlet test pressure of 33 atmospheres . The theoretical development predicts, and the experimental results verify, that the m a x i m u m nozzle thrust is obtained from an area ratio less than that required for complete expansion. It is further shown t h a t thrust equal to t h a t for complete expansion may be obtained from a nozzle having an area ratio of l i tt le more than half of that required for complete expansion.