Abstract
The efficiency of an axially symmetric convergent-divergent micronozzle expander at zero ambient pressure is studied. Its contribution to total thrust is considered by analyzing the relative thrust determined as thrust of the expander computed to nozzle thrust without it. An inviscid one-dimensional flow was considered as the starting point for the subsequent analysis. For that inviscid one-dimensional flow model, expander of infinite length obtains finite relative thrust. Theoretical analysis of shear stress influence shows the existence of an optimal length for the expander. The value of the optimal length evidently depends on the shape of the expander wall. This conclusion was numerically confirmed by results from numerical simulations made for various axisymmetric nozzles. Navier-Stokes equations were used for the numerical simulations. Detailed analysis of flow properties shows that the expander having a wall partially inclined to the axis of symmetry has sometimes higher relative thrust than a similar traditional one due to the appearance of local circulation zones with non-zero bottom pressure resulting in additional thrust force.Reliable numerical analysis of micronozzle flows allows avoiding nozzle “blockage” with corresponding crucial decrease in thrust force and loss of spacecraft maneuverability. In addition, discussed circulation zones can negatively influence optical equipment and solar batteries of a space vehicle due to the low speed of exhaust gas flows near their surface and, consequently, deposition of fuel particles. So the problem of micronozzle optimization evidently belongs to space flight safety issues.
Published Version
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