scholarly journals Installed Performance Assessment of an Array of Distributed Propulsors Ingesting Boundary Layer Flow

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Chana Goldberg ◽  
Devaiah Nalianda ◽  
Panagiotis Laskaridis ◽  
Pericles Pilidis
Keyword(s):  
Boundary Layer ◽  
Fuel Consumption ◽  
Flow Characteristics ◽  
Propulsion System ◽  
Accounting System ◽  
Propulsion Systems ◽  
Local Flow ◽  
System A ◽  
Layer Flow

Conventional propulsion systems are typically represented as uninstalled systems to suit the simple separation between airframe and engine in a podded configuration. However, boundary layer ingesting systems are inherently integrated, and require a different perspective for performance analysis. Simulations of boundary layer ingesting propulsions systems must represent the change in inlet flow characteristics, which result from different local flow conditions. In addition, a suitable accounting system is required to split the airframe forces from the propulsion system forces. The research assesses the performance of a conceptual vehicle, which applies a boundary layer ingesting propulsion system—NASA's N3-X blended wing body aircraft—as a case study. The performance of the aircraft's distributed propulsor array is assessed using a performance method, which accounts for installation terms resulting from the boundary layer ingesting nature of the system. A “thrust split” option is considered, which splits the source of thrust between the aircraft's main turbojet engines and the distributed propulsor array. An optimum thrust split (TS) for a specific fuel consumption at design point (DP) is found to occur for a TS value of 94.1%. In comparison, the optimum TS with respect to fuel consumption for the design 7500 nmi mission is found to be 93.6%, leading to a 1.5% fuel saving for the configuration considered.

scholarly journals Installed Performance Assessment of an Array of Distributed Propulsors Ingesting Boundary Layer Flow

2017 ◽  
Author(s):  
Chana Goldberg ◽  
Devaiah Nalianda ◽  
Pericles Pilidis
Keyword(s):  
Boundary Layer ◽  
Fuel Consumption ◽  
Propulsion System ◽  
Accounting System ◽  
Local Flow ◽  
System A ◽  
Maximum Payload ◽  
Aircraft Performance ◽  
Layer Flow

Conventional propulsion systems are typically represented as uninstalled system to suit the simple separation between airframe and engine in a podded configuration. However, boundary layer ingesting systems are inherently integrated, and require a different perspective for performance analysis. Simulations of boundary layer ingesting propulsions systems must represent the change in inlet flow characteristic which result from the local flow condition. In addition, a suitable accounting system is required to split the airframe forces from the propulsion system forces. The research assesses the performance of a conceptual vehicle which applies a boundary layer ingesting propulsion system — NASA’s N3-X blended wing body aircraft — as a case study. The performance of the aircraft’s distributed propulsor array is assessed using a performance method which accounts for installation terms resulting from the boundary layer ingesting nature of the system. A ‘thrust split’ option is considered which splits the source of thrust between the aircraft’s main turbojet engines and the distributed propulsor array. An optimum thrust split for a specific fuel consumption at cruise is found to occur for a thrust split value of 93%, for the configuration considered. In comparison, the optimum thrust split with respect to fuel consumption for the design 7500 nmi mission is found to be 91.5%. Aircraft performance estimates suggest the N3-X could achieve a maximum payload range of approximately 13650 nautical miles.

scholarly journals Spiral trajectories induced by radial thrust with applications to generalized sails

Astrodynamics ◽  
2020 ◽  
Author(s):  
Marco Bassetto ◽  
Alessandro A. Quarta ◽  
Giovanni Mengali ◽  
Vittorio Cipolla
Keyword(s):  
Equations Of Motion ◽  
Propulsion System ◽  
Point Of View ◽  
Propulsion Systems ◽  
Spiral Trajectory ◽  
System A ◽  
Spiral Trajectories ◽  
Radial Thrust ◽  
Heliocentric Orbit

AbstractIn this study, new analytical solutions to the equations of motion of a propelled spacecraft are investigated using a shape-based approach. There is an assumption that the spacecraft travels a two-dimensional spiral trajectory in which the orbital radius is proportional to an assigned power of the spacecraft angular coordinate. The exact solution to the equations of motion is obtained as a function of time in the case of a purely radial thrust, and the propulsive acceleration magnitude necessary for the spacecraft to track the prescribed spiral trajectory is found in a closed form. The analytical results are then specialized to the case of a generalized sail, that is, a propulsion system capable of providing an outward radial propulsive acceleration, the magnitude of which depends on a given power of the Sun-spacecraft distance. In particular, the conditions for an outward radial thrust and the required sail performance are quantified and thoroughly discussed. It is worth noting that these propulsion systems provide a purely radial thrust when their orientation is Sun-facing. This is an important advantage from an engineering point of view because, depending on the particular propulsion system, a Sun-facing attitude can be stable or obtainable in a passive way. A case study is finally presented, where the generalized sail is assumed to start the spiral trajectory from the Earth’s heliocentric orbit. The main outcome is that the required sail performance is in principle achievable on the basis of many results available in the literature.

scholarly journals Homotopy pertubation method analysis to MHD flow of a radiative nanofluid with viscous dissipation and ohmic heating over a stretching porous plate

2018 ◽  
Vol 22 (1 Part B) ◽  
pp. 413-422 ◽  
Author(s):  
Hitesh Kumar
Keyword(s):  
Boundary Layer ◽  
Viscous Dissipation ◽  
Reverse Flow ◽  
Ohmic Heating ◽  
Complete Solution ◽  
Porous Plate ◽  
Flow Characteristics ◽  
Mhd Flow ◽  
Future Research ◽  
Layer Flow

An analytical study is performed to explore the flow and heat transfer characteristics of nanofluid (Al2O3-water and TiO3-water) over a linearly stretching porous sheet in the presence of radiation, ohmic heating, and viscous dissipation. Homotopy perturbed method is used and complete solution is presented, the results for the nanofluids velocity and temperature are obtained. The effects of various thermophysical parameters on the boundary-layer flow characteristics are displayed graphically and discussed quantitatively. The effect of viscous dissipation on the thermal boundary-layer is seen to be reverse after a fixed distance from the wall, which is very strange in nature and is the result of a reverse flow. The finding of this paper is unique and may be useful for future research on nanofluid.

Studies on Characteristic Frequency and Length Scale of Shock Induced Motion in Transonic Diffuser Using a High Order LES Approach

2015 ◽  
Author(s):  
Debasish Biswas ◽  
Tomohiko Jimbo
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Unsteady Flow ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Propulsion Systems ◽  
Shock Oscillation ◽  
Shock Location ◽  
Suction Slot

Unsteady transonic flows in diffuser have become increasingly important, because of its application in new propulsion systems. In the development of supersonic inlet, air breathing propulsion systems of aircraft and missiles, detail investigations of these types of flow behavior are very much essential. In these propulsion systems, naturally present self-sustaining oscillations, believed to be equivalent to dynamically distorted flow fields in operational inlets, were found under all operating conditions. The investigations are also relevant to pressure oscillations known to occur in ramjet inlets in response to combustor instabilities. The unsteady aspects of these flows are important because the appearance of undesirable fluctuations generally impose limitation on the inlet performance. Test results of ramjet propulsion systems have shown undesirable high amplitude pressure fluctuations caused by the combustion instability. The pressure fluctuations originated from the combustor extend forward into the inlet and interact with the diffuser flow-field. Depending on different parameters such as the diffuser geometry, the inlet/exit pressure ratio, the flow Mach number, different complicated phenomena may occur. The most important characteristics are the occurrence of shock induced separation, the length of separation region downstream of the shock location, and the oscillation of shock location as well as the oscillation of the whole downstream flow. Sajben experimentally investigated in detail the time mean and unsteady flow characteristics of supercritical transonic diffuser as a function of flow Mach number upstream the shock location and diffuser length. The flows exhibited features similar to those in supersonic inlets of air-breathing propulsion systems of aircraft. A High-order LES turbulence model developed by the author is assessed with experimental data of Sajben on the self-excited shock oscillation phenomena. The whole diffuser model configuration including the suction slot located at certain axial location around the bottom and side walls to remove boundary layer, are included in the present computation model. The time-mean and unsteady flow characteristics in this transonic diffuser as a function of flow Mach number and diffuser length are investigated in detail. The results of study showed that in the case of shock-induced separation flow, the length and thickness of the reverse flow region of the separation-bubble change, as the shock passed through its cycle. The instabilities in the separated layer, the shock /boundary layer interaction, the dynamics of entrainment in the separation bubble, and the interaction of the travelling pressure wave with the pressure fluctuation region caused by the step-like structure of the suction slot play very important role in the shock-oscillation frequency.

Flow Characteristics around Circular Cylinders with a Normal Slit

2017 ◽  
Vol 379 ◽  
pp. 48-57 ◽  
Author(s):  
Cheng Hsiung Kuo ◽  
Hwa Wei Lin ◽  
Chih Tao Chai ◽  
Fred Cheng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Flow ◽  
Rear Surface ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Phase Lock ◽  
Layer Flow

Alterations of boundary layer separation along the upper-rear surface of a baseline and slit cylinder and the formation of a vortex in the near-wake are investigated by particle image velocimetry (PIV) at Reynolds number 1000. The slit ratio (S/D) is 0.3. The phase-lock flow structures are referred to the time-dependent volume flux at the slit exit and are achieved by the modified phase-averaged technique. The alterations and the evolution of boundary-layer flow along the upper-rear surface are demonstrated by the phase-lock flow structures. It is found that the alternate blowing and suction at the slit exit serves as a perturbation to the boundary layer near the shoulder of the slit cylinder leading to a significant delay of flow separation and the flow reattachment of boundary-layer flow along the upper-rear surface of the cylinder. After perturbation, the vortex street behind a slit cylinder is more organized and stronger than that behind a baseline cylinder at Reynolds number 1000.

Cycle Flexibility: It’s Impact on V/STOL Tactical Aircraft Propulsion Systems

1972 ◽  
Author(s):  
C. A. Hoelzer ◽  
R. A. Cea
Keyword(s):  
Fuel Consumption ◽  
Parametric Study ◽  
Water Injection ◽  
Great Emphasis ◽  
Propulsion System ◽  
Propulsion Systems ◽  
Variable Turbine Geometry ◽  
Aircraft Systems ◽  
Reasonable Range ◽  
Aircraft Propulsion

The design of a V/STOL aircraft, incorporating only one lift-cruise engine places great emphasis on the flexibility of its propulsion system to provide sufficient thrust for take-off and efficient fuel consumption for cruise. In order to attain a reasonable range with a lightweight vehicle this inconsistency of thrust and SFC mis-match must be resolved. A brief survey of engine technology predictions for the next decade indicates that future aircraft systems would be offered a wider choice of cycle characteristics, higher technology levels, and added cycle flexibility. A comparative parametric study was conducted to determine the effect of these advancements on a postulated 1983 V/STOL aircraft. In particular the effect of increasing thrust through the use of thrust lapse-rating and variable turbine geometry were compared to more conventional augmentors such as duct burning and water injection. Additionally, the effects of varying cycle characteristics to realize SFC improvements were investigated.

Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part B — Scale-Resolving Simulations

2015 ◽  
Author(s):  
Bastian Drechsel ◽  
Christoph Müller ◽  
Florian Herbst ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Numerical Approach ◽  
Pressure Recovery ◽  
Experimental Investigations ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Local Flow ◽  
Coherent Vortices

This paper examines the diffuser flow with consideration to turbine outflow conditions. The setup consists of a low-speed axial diffuser test rig, that represents a 1/10 scaled heavy-duty exhaust diffuser with an annular and a conical diffuser part. In part A of this paper it was shown through experimental investigation that the turbulent kinetic energy as well as the Reynolds shear stresses are the relevant physical parameters that correlate with diffuser pressure recovery. To complement the experimental investigations, unsteady scale-resolving CFD simulations are performed, applying the SST-SAS turbulence model. As a first step, the numerical approach is validated by means of the experimental data with regards to the diffuser’s integral parameters as well as the prediction of local flow characteristics. In a second step, the interaction of coherent vortices generated by the rotor and the diffuser’s boundary layer are analyzed by means of the validated SST-SAS results. These vortices are found to have a major impact on the boundary layer separation in the region immediately downstream of the rotor and at the diffuser inlet.

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