Amer Chpoun

Bio: Amer Chpoun is an academic researcher from University of Évry Val d'Essonne. The author has contributed to research in topics: Nozzle & Rocket engine nozzle. The author has an hindex of 7, co-authored 21 publications receiving 154 citations.

Thrust shock vector control of an axisymmetric conical supersonic nozzle via secondary transverse gas injection

Abstract: Transverse secondary gas injection into the supersonic flow of an axisymmetric convergent–divergent nozzle is investigated to describe the effects of the fluidic thrust vectoring within the framework of a small satellite launcher. Cold-flow dry-air experiments are performed in a supersonic wind tunnel using two identical supersonic conical nozzles with the different transverse injection port positions. The complex three-dimensional flow field generated by the supersonic cross-flows in these test nozzles was examined. Valuable experimental data were confronted and compared with the results obtained from the numerical simulations. Different nozzle models are numerically simulated under experimental conditions and then further investigated to determine which parameters significantly affect thrust vectoring. Effects which characterize the nozzle and thrust vectoring performances are established. The results indicate that with moderate secondary to primary mass flow rate ratios, ranging around 5 %, it is possible to achieve pertinent vector side forces. It is also revealed that injector positioning and geometry have a strong effect on the shock vector control system and nozzle performances.

Assessment of gas thermodynamic characteristics on fluidic thrust vectoring performance: Analytical, experimental and numerical study

Abstract: The cross injection in a supersonic flow is an issue encountered in several aerodynamic applications such as fuel injection in scramjet combustor, missile control, drag reduction and thrust vector control. In a recent work, an analytical model has been presented to calculate the fluidic thrust vectoring performance for a supersonic axisymmetric nozzle. The model is able to take into account both the injected gas thermodynamic properties and the geometrical nozzle characteristics. The analytical model has been successfully validated following the cold air flow experimental analysis, in the case of fluidic thrust vectoring applied to conical nozzle. The aim of this work is to show how far the injected gas thermodynamic properties, different from that of the nozzle main flow, could influence the fluidic thrust vectorization parameters. In this work, the experimental performance of the fluidic thrust vectoring concept, using numbers of gases as injectant, has been qualitatively and quantitatively analyzed. Schlieren visualization, force balance and wall pressure measurements were used in the case of a truncated ideal contour nozzle. The experimental results are compared to the numerical and analytical findings. Performance analysis are conducted and basic conclusions are drawn in terms of thermodynamic gas properties effect on the fluidic thrust vector system. The primary effect was related to the gas molecular weight and its specific heat ratio product. It is observed that for fixed injection conditions, the vectoring angle is higher when the injected gas molecular weight and specific heat ratio product is less than that of the primary gas. For a given mission of the launcher, it can be concluded that the mass of the embedded gas, used for the fluidic vectorization system, can be significantly reduced, depending on its molecular weight and specific heat ratio.

Experimental–Numerical Parametric Investigation of a Rocket Nozzle Secondary Injection Thrust Vectoring

Abstract: Secondary transverse injection into the divergent section of an axisymmetric convergent–divergent propulsive nozzle is investigated for the fluidic thrust vectoring effects. Coupled experimental and numerical cold-flow investigation on the number of cases and aspects was conducted in the framework of a French microsatellite launcher program. Five experimental test nozzles were designed, built, and equipped with diagnostic tools. All experimental test models were supported by full three-dimensional numerical simulations and further investigated using the additional nozzle models, cases, and analysis parameters. Pertinent side force and pitch vector angle of 5–9 deg were achieved within the 5–8% range of the secondary to primary mass-flow-rate ratio. Investigation aspects, categorized as the nozzle vectoring system geometrical characteristics, primary and secondary flow conditions, and gas intrinsic properties were found to dominantly affect the thrust vectoring capabilities. Some further improvements are s...

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

Abstract: 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 a...

Fluidic thrust vectoring of an axisymmetrical nozzle: an analytical model

Abstract: 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.

Effects of upstream boundary layer on the unsteadiness of shock induced separation

Abstract: The relationship between the upstream boundary layer and the low-frequency, large-scale unsteadiness of the separated flow in a Mach 2 compression ramp interaction is investigated by performing wide-field particle image velocimetry (PIV) and planar laser scattering (PLS) measurements in streamwise–spanwise planes. Planar laser scattering measurements in the upstream boundary layer indicate the presence of spanwise strips of elongated regions of uniform momentum with lengths greater than 40?. These long coherent structures have been observed in a Mach 2 supersonic boundary layer (Ganapathisubramani, Clemens & Dolling 2006) and they exhibit strong similarities to those that have been found in incompressible boundary layers (Tomkins & Adrian 2003; Ganapathisubramani, Longmire & Marusic 2003). At a wall-normal location of y/?=0.2, the inferred instantaneous separation line of the separation region is found to oscillate between x/?=?3 and ?1 (where x/?=0 is the ramp corner). The instantaneous spanwise separation line is found to respond to the elongated regions of uniform momentum. It is shown that high- and low-momentum regions are correlated with smaller and larger size of the separation region, respectively. Furthermore, the instantaneous separation line exhibits large-scale undulations that conform to the low- and high-speed regions in the upstream boundary layer. The low-frequency unsteadiness of the separation region/shock foot observed in numerous previous studies can be explained by a turbulent mechanism that includes these elongated regions of uniform momentum

Aerodynamics of small vehicles

Abstract: In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.

Literature Survey of Numerical Heat Transfer (2000–2009): Part II

Abstract: A comprehensive survey of the literature in the area of numerical heat transfer (NHT) published between 2000 and 2009 has been conducted Due to the immenseness of the literature volume, the survey

Numerical simulation of fluidic thrust vectoring in an axisymmetric supersonic nozzle

Abstract: Transverse secondary gas injection into an axisymmetric supersonic nozzle under standard atmosphere pressure is investigated to get the performance of thrust vectoring control. An analytical model was established based on the transverse injection flow. Three-dimensional CFD methods were performed with different transverse secondary injection models. To validate the ability of the numerical model, numerical results were compared with the analytical and experimental results. Overall pressure distributions show quite good match with the analytical and experimental results. The Mach number contours in different injection positions were obtained. Reflection of the bow shock occurred for xj/L = 0.6, not for xj/L = 0.9. Nozzle pressure ratio is also the key factor for shock vector control. Based on this data, thrust vectoring efficiency and system thrust ratio have been considered. Finally, the pressure distributions in different momentum flux ratios were studied in CFD and analytical models. The separating point of boundary layer is moving upstream with the increasing of momentum flux ratio. The result will provide the reference to the further development of shock vector control.

Thrust shock vector control of an axisymmetric conical supersonic nozzle via secondary transverse gas injection

Abstract: Transverse secondary gas injection into the supersonic flow of an axisymmetric convergent–divergent nozzle is investigated to describe the effects of the fluidic thrust vectoring within the framework of a small satellite launcher. Cold-flow dry-air experiments are performed in a supersonic wind tunnel using two identical supersonic conical nozzles with the different transverse injection port positions. The complex three-dimensional flow field generated by the supersonic cross-flows in these test nozzles was examined. Valuable experimental data were confronted and compared with the results obtained from the numerical simulations. Different nozzle models are numerically simulated under experimental conditions and then further investigated to determine which parameters significantly affect thrust vectoring. Effects which characterize the nozzle and thrust vectoring performances are established. The results indicate that with moderate secondary to primary mass flow rate ratios, ranging around 5 %, it is possible to achieve pertinent vector side forces. It is also revealed that injector positioning and geometry have a strong effect on the shock vector control system and nozzle performances.