Amer Chpoun

Fluidic thrust vectoring of an axisymmetrical nozzle: an analytical model

An engineering-type analysis is proposed and used to investigate the performances of thrust vectoring by fluidic injection in the divergent of a supersonic axisymmetrical convergent-divergent nozzle. This method includes several approaches which consist mainly of a fluidic obstacle height evaluation and the prediction of the separation line that results upstream of the fluidic obstacle. The construction of the separation line is also based on some separation correlations proposed in the literature. The nozzle thrust deviation is then calculated by taking into account the injectant fluid momentum rate contribution and the integration of the pressure acting on the nozzle inner wall. The sensitivity of the model versus some separation criteria is discussed. The results of the analytical model are compared with the experiments conducted recently by the authors. The comparison shows a very good agreement for some of the separation criteria over the whole range of injected to main flow-rate ratios.

Numerical Study of Heat Transfer Around the Small Scale Airfoil Using Various Turbulence Models

A numerical investigation of low-Reynolds number flows with thermal effect around the MAV airfoils using various turbulence models, including an algebraic Baldwin-Lomax model, Spalart-Allmaras one equation, and two equation (k-ω and SST-k-ω) turbulence models, is presented. First, the thermal effect on the aerodynamic efficiency is studied for flow around a rectangular MAV wing, based on the NACA0012 airfoil section at low-aspect ratio (AR = 2) and an angle of attack equal to 0°. Second, details of the thermal effect are limited to the two-dimensional NACA0012 airfoil with chord length of 3.81 cm. This study shows that the improvement of aerodynamic efficiency (increase lift and reduce drag) is achieved by the generation of a temperature difference between extrados and intrados of the airfoil (by cooling the upper surface and heating the lower surface). The numerical results obtained with various turbulence models are in good agreement with experiment data, except the k-ω turbulence model. These results are performed with the CFD-FASTRAN code, using the fully implicit scheme for time integration and the upwind Roe flux difference splitting scheme for space discretization augmented by a high order Osher-Chakravarthy limiter.

Experimental and Numerical Study of Thrust-Vectoring Effects by Transverse Gas Injection into a Propulsive Axisymmetric C-D Nozzle

Transverse gas injection into a divergent section of a convergent-divergent rocket nozzle have been investigated for thrust vectoring effects as the segment part of the CNES Perseus program. Cold flow experiments on conical and truncated ideal nozzles have been conducted in the hypersonic windtunnel EDITH. These experiments are compared and complemented by the numerical investigation results of the compressible FANS numerical solver CPS C. Number of parameters and performance criteria have been examined and reported. It is found that pertinent vector force is possible to be achieved via such fluidic thrust vectoring system.

Numerical Simulation of Reactive Flows in Overexpanded Supersonic Nozzle with Film Cooling

Reignition phenomena occurring in a supersonic nozzle flow may present a crucial safety issue for rocket propulsion systems. These phenomena concern mainly rocket engines which use H2 gas (GH2) in the film cooling device, particularly when the nozzle operates under over expanded flow conditions at sea level or at low altitudes. Consequently, the induced wall thermal loads can lead to the nozzle geometry alteration, which in turn, leads to the appearance of strong side loads that may be detrimental to the rocket engine structural integrity. It is therefore necessary to understand both aerodynamic and chemical mechanisms that are at the origin of these processes. This paper is a numerical contribution which reports results from CFD analysis carried out for supersonic reactive flows in a planar nozzle cooled with GH2 film. Like the experimental observations, CFD simulations showed their ability to highlight these phenomena for the same nozzle flow conditions. Induced thermal load are also analyzed in terms of cooling efficiency and the results already give an idea on their magnitude. It was also shown that slightly increasing the film injection pressure can avoid the reignition phenomena by moving the separation shock towards the nozzle exit section.

Effects of the inlet gases thermodynamic properties on a fluidically thrust vectorized supersonic nozzle

Effects of the primary and secondary inlet gases properties on the fluidically vectorized axisymmetric supersonic nozzle performances have been investigated following previous cold flow analysis in the framework of the CNES Perseus program. Sonic injection of different gases into the dry air supersonic flow of convergent-divergent axisymmetric nozzle are tested in hypersonic test facility EDITH of the CNRS institute ICARE. Effects are analyzed qualitatively via color schlieren visualization and quantitatively in terms of parietal pressure data and force balance measurements. The results are then confronted to the ones from numerical simulation performed using the solver of the CNES and Bertin CFD code CPS C. Performance analysis is conducted on the coupled numerical-experimental data and basic conclusions are drawn on gas properties effect on a fluidic vector system. Further numerical simulations are then performed with hot combusted gases inlet conditions. Major consequences on FTV system are depicted and given in the Result and Conclusion sections.