Aerodynamic performance of a bypass engine with fan nozzle exit area change by warped chevrons

Variation of the bypass nozzle exit area enables optimization of the turbofan engine operating cycle over a wider range of operational conditions resulting in improved thrust and/or fuel consumption. Two mechanisms for varying the nozzle area have been investigated. The first uses an array of chevrons which when closed, form a full body of revolution and when warped/curved, increase the exit area while forming a serrated trailing edge. The second technique incorporates an axially translating section of the nacelle shroud and uses the change in the nozzle boat-tail radial location with the axial location as a means to vary the nozzle exit area. To analyse the effects on a typical rotor/stator stage, computational fluid dynamics simulations of the NASA Rotor 67, Stator 67A stage integrated into a custom-built nacelle were performed. Nozzles with 8, 12, and 16 chevrons were simulated to evaluate the impact of the variation in geometry upon the nacelle wake and local forces. Gross thrust of the nacelle and the turbulent kinetic energy (TKE) variation through the wake is compared. The chevron nozzle attains a nearly 2 per cent maximum thrust improvement over the translating nozzle technique. The chevron nozzle also has significantly lower (nearly 8 per cent) peak TKE levels in the jet plume.

Flowfield analysis of a linear clustered plug nozzle with round-to-square modules

The plug nozzle is one of the advanced expansion devices proposed to improve the overall performance of launcher liquid rocket engines. The present work investigates the three-dimensional flow field generated on this kind of nozzle by partitioning the primary nozzle into modules. A linear plug nozzle has been designed together with modules having two different geometries: a rectangular cross section and round-to-square module. Numerical simulations have been carried out considering the case where all modules of the primary nozzle are active and the case where one module is turned off. The solutions are compared and specific three-dimensional flow structures taking place inside the modules and on the plug are identified. The relationship between these structures and the skin friction distribution within the module and along the plug surface is investigated. Finally, the effect on performance of these three-dimensional flow features is emphasized. © 2006 Elsevier Masson SAS. All rights reserved.

Performance analysis of an infinite array linear clustered plug nozzle

The effects of module shape, module design, three dimensional flow field generated by modules, and partition of primary nozzle on the performance of an infinite array linear clustered plug nozzle are discussed. The module shape is a critical element for nozzle performance and the partition of the primary nozzle with round-to square modules causes a vacuum thrust reduction with respect to two-dimensional model. The performance analysis of different module configuration allows weighing separately the role of clustering and the role of module design. In operating conditions characterized by turned off modules the performance loss is larger, but the difference due to the module shape are smaller and mostly due to the module contribution. The performance of the plug nozzle can be improved by module design, which reduces the module exit flow nonuniformity.

The effect of nozzle geometry on the flow characteristics of small water jets

A wide variety of processes make use of plain orifice nozzles. Fuel injectors for internal combustion engines incorporate these nozzles to generate finely atomized sprays. Processes such as jet cutting, jet cleaning, and hydroentanglement, on the other hand, use similar nozzles, but require coherent jets. The spray or jet characteristics depend on the stability of the flow emerging from the orifice. This problem has been extensively researched for nozzles with diameters above 300 μm. Much less is known about the characteristics of jets produced by nozzles with smaller diameters, where viscous effects and small geometric variations due to manufacturing tolerances are likely to play an increasing role. Results are presented of a wide-ranging investigation of geometry effects on the flow parameters and jet characteristics of nozzles with diameters between 120 and 170 μm. Nozzles with circular cross-section and conical, cone-capillary and capillary axial designs were investigated. For conical and cone-capillary nozzles, the effect of cone angle and effects due to interactions between adjacent nozzles in the multi-hole cone-capillary nozzles were studied. For capillary nozzles, the effects of diameter variations and inlet edge roundness for capillary nozzles were considered. Furthermore, the effect of varying the aspect ratio (ratio of major and minor axes) of elliptical nozzles was studied. Flowrate and jet impact force measurements were carried out to determine the discharge coefficient C, velocity coefficient C, and contraction coefficient C of the nozzles for supply pressures between 3 and 12 MPa. Visualizations of the jet flow were carried out in the vicinity of the nozzle exit in order to identify near-nozzle flow regimes and to study jet coherence. The relationship between nozzle geometry, discharge characteristics, and jet coherence is examined. © IMechE 2006.

Effect of nozzle geometry on the flow characteristics of hydroentangling jets

Cone-capillary nozzles with varying cone angles from 10° to 120° and a capillary diameter of 120μ are experimentally investigated for their application in the hydroentanglement process. Cone-up and cone-down configurations in a range of water pressures of 30-120 bar are tested. The effects of the cone angle on flow parameters such as discharge and velocity coefficients and intact length are studied. Flow visualization techniques are used to recognize the flow regimes and characteristics and to inspect and compare the intact length and appearance of the jets. Cone-down nozzles with more consistent flow properties, lower discharges, and higher velocity coefficients are more suitable for the hydroentanglement process. Single-cone nozzles without capillaries and with varying cone angles are also tested. The flow properties of the jets from the single-cone nozzles are compared with the cone-capillary nozzles of the same cone angle to study the effect of the capillary section. The effect of the interaction of adjacent nozzles on the flow from multi-hole nozzles is studied, and the characteristics of the jets from the multi-hole nozzles are compared with the single-hole nozzles.

Passive Control of Plume Interference on Slender Axisymmetric Bodies

The physics of the plume-induced shock and separation, particularly at high plume to exit pressure ratios with and without shock-turbulent boundary-layer control methods, were studied using computational techniques. Mass-averaged Navier-Stokes equations with a two-equation turbulence model were solved by using a fully implicit finite volume scheme and time.marching algorithm. The control methodologies for shock interactions included a porous tail and a porous extension attached at the nozzle exit or trailing edge. The porous tail produced a weaker shock and fixed the shock position on the control surface. The effect of the porous extension on shock interactions was mainly to restrain the plume from strongly underexpanding during a change in flight conditions. These techniques could give an additional dimension to the design and control of supersonic missiles.

Absolute Atomic Oxygen Density Measurements by Two-Photon Absorption Laser-induced Fluorescence Spectroscopy in an RF-Excited Atmospheric Pressure Plasma Jet

The atmospheric pressure plasma jet is a capacitively coupled radio frequency discharge (13.56 MHz) running with a high helium flux (2m3 h-1) between concentric electrodes. Small amounts (0.5%) of admixed molecular oxygen do not disturb the homogeneous plasma discharge. The jet effluent leaving the discharge through the ring-shaped nozzle contains high concentrations of radicals at a low gas temperature—the key property for a variety of applications aiming at treatment of thermally sensitive surfaces. We report on absolute atomic oxygen density measurements by two-photon absorption laser-induced fluorescence (TALIF) spectroscopy in the jet effluent. Calibration is performed with the aid of a comparative TALIF measurement with xenon. An excitation scheme (different from the one earlier published) providing spectral matching of both the two-photon resonances and the fluorescence transitions is applied.

Generation of Atomic Oxygen in the Effluent of an Atmospheric Pressure Plasma Jet

The planar 13.56MHz RF-excited low temperature atmospheric pressure plasma jet (APPJ) investigated in this study is operated with helium feed gas and a small molecular oxygen admixture. The effluent leaving the discharge through the jet’s nozzle contains very few charged particles and a high reactive oxygen species’ density. As its main reactive radical, essential for numerous applications, the ground state atomic oxygen density in the APPJ’s effluent is measured spatially resolved with two-photon absorption laser induced fluorescence spectroscopy. The atomic oxygen density at the nozzle reaches a value of ~1016 cm-3. Even at several centimetres distance still 1% of this initial atomic oxygen density can be detected. Optical emission spectroscopy (OES) reveals the presence of short living excited oxygen atoms up to 10 cm distance from the jet’s nozzle. The measured high ground state atomic oxygen density and the unaccounted for presence of excited atomic oxygen require further investigations on a possible energy transfer from the APPJ’s discharge region into the effluent: energetic vacuum ultraviolet radiation, measured by OES down to 110 nm, reaches far into the effluent where it is presumed to be responsible for the generation of atomic oxygen.

Screening wall effects of a thin fluidized bed by near-infrared imaging

Near-infrared (NIR) imaging was used to observe water vapour flow in a gas-solid fluidized bed reactor. The technique consisted of a broadband light, an optical filter with a bandwidth centred on strong water vapour absorptions, a Vidicon NIR camera, a nozzle from which an optically active mixture of gas and water vapour was trans-illuminated by an NIR beam and collected data of transmittance were normalized to actual optical path. The procedure was applied to a thin fluidized bed reactor with a low aspect ratio of tube to particle diameters (D-1/d(p)) in order to validate the wall effect on flow dynamics and mass transfer during the reduction of ceria-silica by hydrogen. High concentrations of water vapour emerged in the vicinity of the wall when the bed was operated at pseudo-static conditions but disappeared when the bed was run at minimum bubbling conditions. This result shows the capability of optical methods with affordable costs to 2D imaging opaque packed bed by using a spatially resolved probe located at the exit, which is of great benefit for in situ visualization of anisotropic concentrations in packed beds under industrially relevant conditions and thus for elucidation of the underlying reaction mechanism and diffusion interactions. Crown Copyright (c) 2011 Published by Elsevier B.V. All rights reserved.

Generation of bright, extreme-ultraviolet harmonic radiation from a krypton fluoride laser

We present results of experiments studying the efficiency of high harmonic generation from a gas target using the TITANIA krypton fluoride laser at the Rutherford Appleton Laboratory. The variation of harmonic yield for the 7th to 13th harmonics (355-191 Angstrom) is studied as a function of the backing pressure of a solenoid valve gas jet and of the axial position of the laser focus relative to the centre of the gas jet nozzle. Harmonic energies up to 1 mu J were produced in helium and neon targets from laser energies of approximately 200 mJ. This corresponds to absolute conversion efficiencies of up to 5 x 10(-6).

Ethanol (C2H5OH) spray of sub-micron droplets for laser driven negative ion source

Liquid ethanol (C₂H₅OH) was used to generate a spray of sub-micron droplets. Sprays with different nozzle geometries have been tested and characterised using Mie scattering to find scaling properties and to generate droplets with different diameters within the spray. Nozzles having throat diameters of 470 µm and 560 µm showed generation of ethanol spray with droplet diameters of (180 ± 10) nm and (140 ± 10) nm, respectively. These investigations were motivated by the observation of copious negative ions from these target systems, e.g., negative oxygen and carbon ions measured from water and ethanol sprays irradiated with ultra-intense (5 × 1019 W/cm2), ultra short (40 fs) laser pulses. It is shown that the droplet diameter and the average atomic density of the spray have a significant effect on the numbers and energies of accelerated ions, both positive and negative. These targets open new possibilities for the creation of efficient and compact sources of different negative ion species.