Subsonic Operation Research Articles

Impact of atomization and spray flow conditions on droplet [formula omitted]-explosions and temporal self-similarity in the FSP process

Flame spray pyrolysis (FSP) is a technique for the synthesis of metal oxide nanoparticles by combusting precursor solutions in a spray flame. The combustion of certain precursor solutions is known to lead to severe droplet disruptions (μ-explosions) in the spray flame that are linked to the synthesis of homogeneous and phase-pure nanoparticles. In this work, a broad spectrum of suitable subsonic operating conditions for the synthesis of iron oxide nanoparticles by FSP is investigated to understand the influence of the jet Reynolds number and turbulence on the onset of μ-explosions and droplet dynamics in spray flames. In order to enable a coherent comparison between differently operated spray flames using an iron(III) nitrate nonahydrate solution, the gas-to-liquid mass ratio and, hence, the oxygen/fuel ratio have been kept constant in order to identify the influence of flow conditions on the droplet dynamics. From the analysis of the droplet sizes in the spray and in the spray flame, it is found that in all combusting sprays, the droplet sizes convert from unimodal (after atomization) to bimodal droplet size distribution (DSD) due to the presence of μ-explosions. The occurrence and evolution of the bimodal DSD reveal that high jet Reynolds numbers result in narrower DSD and in a sharper separation of both DSD probability peaks (modal values). A straightforward 1-step kinematic model is presented to describe the conversion of unimodal to bimodal DSD considering the evaporation of droplets as well as the disruption of droplets to mimic the effect of μ-explosions. The temporal evolution of droplets in FSP is investigated by spatially resolved velocity data that reveal the formation of a temporal self-similarity. The resulting iron oxide nanoparticle size decreases with increasing jet Reynolds number. The turbulent mixing and residence times in the flame, primarily set by the jet Reynolds number, are identified as key design parameters for FSP.

Time-dependent subsonic ablation pressure scalings for soft X-ray heated low- and intermediate-Z materials at drive temperatures of up to 400 eV

The soft X-ray driven subsonic ablation of five different materials with atomic numbers ranging from 3.5 to 22 is investigated for radiation drive temperatures of up to 400eV. Simulations were performed using the one-dimensional radiation hydrodynamics simulation code HYADES. For each material, ablation pressure scaling-laws are determined as a function of drive radiation-temperature and time, assuming that the irradiation lasts for a period of a few nanoseconds and that the drive temperature remains constant during this period. For all the materials, the maximum drive-temperature for subsonic operation is identified. As expected, lower-Z materials demonstrate a stronger scaling of ablation pressure with radiation temperature and a more gradual fall off with time. However, the lowest-Z materials transition to trans- and super-sonic ablation at temperatures of only a few hundred eV.

Wavelet Features and Hidden Markov Model-Based Aerodynamic Instability Detection for Compressors

Abstract A reliable technique is introduced to detect aerodynamic instability of compressors based on wavelet features and hidden Markov model (HMM). A single sensor is sufficient for stall warning if the position of the sensor is carefully selected. The method involves obtaining high-response pressure signal near the rotor tip close to the leading edge. Rotating instabilities band wavelet features are then extracted and trained for the HMM; using data under normal operating conditions, the performance index (PI) is calculated. Unsteady behaviors in prestall processes are discussed and casing wall pressure maps are implemented to explore the mechanism of tip leakage vortex (TLV), which are helpful in explaining the various PI results from different feature selections and probe locations. Experimental results show that the trend indices of PI suitably characterize the compressor aerodynamic instability in subsonic operation.

The influence of booster design features on aicraft engine fan tonal noise

Fan and booster tonal noise makes significant contribution to the overall noise level of an aero engine, particularly in subsonic modes of operation. This noise is caused by the interaction not only of the fan rotor and stator, but also by the interaction of elements of the fan and booster. Tonal components at these frequencies are caused by nonlinear interaction of rotating and stationary blade rows. Therefore, fan noise spectra contain not only common fan tonal components at the blade passing frequency and its harmonics, but sum and difference tones of interaction between the fan and booster elements. In testing acoustic characteristics of a bypass wide-chord fan it was revealed that the sum and difference components of the fan and booster interaction noise appeared in subsonic operating modes and propagated basically in the forward hemisphere. Labyrinth seal is one of the features of the actual fan design. These seals are opened and let some airflow pass in low operating modes of the fan. As a result the flow pattern upstream the fan rotor is distorted. It was experimentally determined that the seal significantly affects the generation of the fan tonal noise in subsonic modes. So far, the impact of this fan design feature is not taken into account in fan noise prediction methods. However, we experimentally determined strong influence of labyrinth seals on the noise of the aero engine simulator. Experimental assessment of the influence of the labyrinth seal operating in off-design modes on UPS noise spectra is the purpose of this work.

Flowing-gas diode pumped alkali lasers: theoretical analysis of transonic vs supersonic and subsonic devices.

We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.

Numerical simulation on operation of closed‐loop experimental facility with subsonic MHD generator

AbstractThe operating characteristics and operation procedure of the closed‐loop experimental facility under subsonic power generation have been investigated by means of time‐dependent quasi‐one‐dimensional numerical simulations. Two ways of operation for subsonic power generation were found: (1) subsonic operation both under nonpower and power generation and (2) supersonic operation under nonpower generation and subsonic operation under power generation. For operation (1), Mach number at channel inlet decreases to ∼0.6, therefore it is required to generate plasma under this Mach number. On the other hand, if the plasma cannot be generated, operation (2) needs to be carried out. In this case, a shock wave appears in the generator channel, then the influence of a large pressure change and a vibration caused by a shock wave in the generator channel needs to be considered. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 25–33, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20399

Subsonic Radiation Gas Dynamics in a Laser Plasma Generator Channel

The radiation gasdynamic processes in the channel of an air laser plasma generator operating at atmospheric pressure are analyzed. In the multigroup approximation a numerical radiation gasdynamic model is formulated on the basis of the equations of motion of a viscous heat-conducting gas and the selective thermal radiation transport equation. Laminar and turbulent subsonic generator operation regimes are considered. For the purpose of approximately describing the turbulent gas and plasma mixing the Navier-Stokes equations averaged after Reynolds and the k-e turbulence model are used. The problem is solved in the time-dependent two-dimensional axisymmetric formulation. Strong radiation-gasdynamic interaction regimes are investigated. In these regimes the energy losses due to radiation from the high-temperature region of the laser plasma and the absorption of its thermal self-radiation by the surrounding plasma and gas layers (radiation reabsorption) appreciably affect the gasdynamic flow structure. Two methods of integrating the selective thermal radiation transport equation in the generator channel are discussed. In one of these the thermal radiation transport is calculated inside the heated volume and in the other the radiation heat fluxes are calculated on the surfaces bounding the volume. The results of calculating the spectral and integral radiation heat fluxes on the inner surface of the generator are given.

Numerical Simulation on Operation of Closed Loop Experimental Facility with Subsonic MHD Generator

The operating characteristics and operation procedure of the closed loop experimental facility under subsonic power generation have been investigated by means of time-dependent quasi-one-dimensional numerical simulations. It was found that there are two ways of operation for the subsonic power generation, which are (1)a subsonic operation both under non-power and power generation and (2)a supersonic operation under non-power generation and subsonic operation under power generation. For the operation(1), Mach number at channel inlet decreases to ˜0.6, therefore it is required to generate plasma under this Mach number. On the other hand, if the plasma cannot be generated, the operation(2) needs to be carried out. In this case, a shock wave appears in the generator channel, then the influence of a large pressure change and a vibration caused by a shock wave in the generator channel needs to be considered.

High-pressure subsonic mode operation of chemical oxygen-iodine laser

A new regime of chemical oxygen-iodine laser (COIL) operation in the high-pressure subsonic mode was demonstrated. 342 W output with 20.9% chemical efficiency was obtained at the Cl/sub 2/ flow rate of 18 mmol/s. The operating pressure at the laser cavity was 6.4 Torr, and it is equivalent to 3.1 J/l of specific energy. The specific energy obtained was four times as high as supersonic operation, and to our knowledge, that is the highest specific energy reported. The experimental results were in good agreement with the numerical simulation results.

High-pressure subsonic mode operation of chemical oxygen-iodine laser

High-pressure subsonic mode operation of chemical oxygen-iodine laser

Accelerators and decelerators for large hypersonic aircraft

H YPERSONIC aircraft will be considerably different from subsonic aircraft. They will be very large, deltoid-configured aircraft with needle noses. Thus their shape will be almost the opposite that of subsonic aircraft which have much higher aspect-ratio wings and raindrop-shaped fuselages. A result of these differences is that hypersonic aircraft will have much higher takeoff and landing speeds, and they will be less efficient when flying at subsonic speeds. To overcome their low-speed inefficiency, more powerful subsonic engines would be required. Since noise increases with power, more noise would be created during subsonic operation. And because of their large size, hypersonic aircraft will generate intense sonic booms when flying at supersonic speeds. With these vast differences it is unreasonable to assume that hypersonic aircraft will be operated the same way as subsonic aircraft, i.e., that they will take off with onboard power and land on a long runway at any large airport. On the contrary, hypersonic aircraft, with their onerous characteristics, will probably be over-the-ocean craft, like the historical flying boats. Thus they will take off and land at only seacoast sites where the noise and sonic boom will be generated over an ocean. With takeoffs and landings at only a few sites, it will be economically feasible to have a considerable amount of ground-based equipment at each site. For good economics the operation of hypersonic aircraft must be very reliable. The use of ground-based, rather than airborne, equipment will increase their operational reliability because: 1) Ground-based equipment does not have the severe weight and volume limitations that airborne equipment has; so it can be designed more conservatively with larger margins of safety. 2) Ground-based equipment does not have to endure the vibrations, large temperature changes, and other hazards of flight. 3) Ground-based equipment will be available for maintenance most of the time. It will not be in the air where it cannot be serviced or repaired. Thus the goal should be to minimize the amount of airborne equipment by developing as much ground-based equipment as can be used. To fulfill this goal it is found that: 1) It is possible to design and build a ground-based accelerator that can precisely control the attitudes of very large aircraft while they are accelerated through the speed of sound and then launch them at a speed of Mach 2. 2) It is also possible to design and build a rotatable, groundbased decelerator that can land a large, fully-loaded aircraft that is traveling at a speed of 450 mph. Presented as Paper 90-1986 at the AIAA/SAE/ASME/ASEE 26th Joint Propulsion Conference, Orlando, FL, July 16-18, 1990; received July 30, 1990; synoptic received March 14, 1991; accepted for publication March 28,1991. Full paper available from AIAA Library, 555 W. 57th Street, New York, NY 10019. Copyright © 1991 by Edward Lantz. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. * Consultant. Associate Fellow AIAA.

High Interaction Subsonic MHD Channel Operation

Analytical and experimental investigations were conducted into the subsonic operation of MHD generator channels. Experiments were performed with a combustion-driven MHD channel in which transitions from supersonic flow to subsonic flow and vice versa were caused by varying the magnetic field strength. Subsonic operation under various conditions was verified by increases in combustor pressure with increases in magnetic field. Experimentally measured operating parameters were compared with predictions. Satisfactory agreement was generally found.

Reducing jet engine noise

Aeroengine noise reduction activity of the recent past has covered the whole system of existing and feasible patterns of operation from short take off concepts through to supersonic transport. In the UK engine industry, however, the emphasis has been on solving three outstanding problems: quietening the noisier of the existing aircraft, the Concorde problem, and designing even quieter engines for future subsonic operation.

Studies of drag-reduction methods for subsonic operation of supersonic inlets.

Two schemes were studied in an attempt to reduce the drag of a supersonic inlet at subsonic speeds. One of the methods is to use a retractable airfoil in front of the cowl to generate thrust. The second method involves hinging the cowl lip inward so that the captured airflow is choked, thus lowering the pressures on the external surfaces. Both schemes were successful in reducing the drag at captured airflow rates less than the choking point of the plain inlet. Although the drag was not reduced below the critical drag of the plain inlet, the tests indicate that this may be possible.

Separation Standards and Aircraft Wander

The basic parameters leading to aircraft navigational error are combined statistically and are used to evaluate the uncorrected deviation (wander) to be expected in both subsonic and supersonic transport aircraft operating in a typical trans-oceanic environment. The size of the across-track and along-track wander before any form of corrective control is applied indicates the physical size of the A.T.C. block of airspace necessary to contain the aircraft. The variation of block size with the forward prediction period used by A.T.C. is presented graphically. The effect of improvement in the basic sources of error is demonstrated and it is seen that for the S.S.T. era attention must be turned to effecting improvements in aircraft heading and airspeed holding capabilities.

The medical aspects of supersonic flight.

AS THE RESULT of more than 10 years of international study it has been established that supersonic air transportation by the early 1970's is technically and economically feasible.1At that time the general flying public will take a substantial step forward on the road to eventual civil space flight.2Although no totally new medical problem areas are anticipated for supersonic flight, the speeds and altitudes envisioned do require a re-evaluation of the inherent operational and environmental hazards with particular emphasis on potential effects on crew, passengers, and the public at large. This report describes this advanced form of air travel and re-examines those areas currently of greatest clinical concern. Configuration The artist's conception of a representative supersonic jet configuration (top right) shows that characteristically, it has a long, narrow, pointed body and either a fixed, razor-thin, delta or a variablegeometry wing designed for both subsonic and supersonic operation.