Unsteady Shock-Flow Characteristics in an Over-Expanded Rocket Nozzle

A numerical investigation of transient side-loads in an axisymmetric over-expanded thrust optimized contour nozzle is presented.These nozzles experience side-loads during start-up and shut-down operations,because of the flow separation at nozzle walls.Two types of flow separations such as FSS and RSS shock structure occur.A two-dimension numerical simulation has been carried out over an axisymmetric TOC nozzle to validate present results and investigate oscillatory flow characteristics for start-up processes.Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme.Governing equations are solved by coupled implicit scheme.Reynolds Stress turbulence model is selected.Present computed pressure at the nozzle wall closely matched with experiment data.A hysteresis phenomenon has been observed between these two shock structures.The transition from FSS to RSS pattern during start-up process has shown maximum nozzle wall pressure.Nozzle wall pressure and shear stress values have shown fluctuations during the FSS to RSS transition. The oscillatory pressure has been observed on the nozzle wall for high pressure ratio.Present results have shown that magnitude of the nozzle wall pressure variation is high for the oscillatory phenomenon.

Comparison of aerodynamic characteristics between a novel highly loaded injected blade with curvature induced pressure-recovery concept and one with conventional design

This paper introduces a novel design method of highly loaded compressor blades with air injection.CFD methods were firstly validated with existing data and then used to develop and investigate the new method based on a compressor cascade.A compressor blade is designed with a curvature induced pressure-recovery concept.A rapid drop of the local curvature on the blade suction surface results in a sudden increase in the local pressure,which is referred to as a curvature induced ‘Shock＇.An injection slot downstream from the ‘Shock＇ is used to prevent ‘Shock＇ induced separation,thus reducing the loss.As a result,the compressor blade achieves high loading with acceptable loss.First,the design concept based on a 2D compressor blade profile is introduced.Then,a 3D cascade model is investigated with uniform air injection along the span.The effects of the incidence are also investigated on emphasis in the current study.The mid-span flow field of the 3D injected cascade shows excellent agreement with the 2D designed flow field.For the highly loaded cascade without injection,the flow separates immediately downstream from the ‘Shock＇;the initial location of separation shows little change in a large incidence range.Thus air injection with the same injection configuration effectively removes the flow separation downstream from the curvature induced ‘Shock＇ and reduces the size of the separation zone at different incidences.Near the endwall,the flow within the incoming passage vortex mixes with the injected flow.As a result,the size of the passage vortex reduces significantly downstream from the injection slot.After air injection,the loss coefficient along spanwise reduces significantly and the flow turning angle increases.