A discussion on advanced methods of energy conversion- Magnetohydrodynamic power generation - Wave growth in m .h.d. generators

1967 ◽  
Vol 261 (1123) ◽  
pp. 461-470 ◽  
Keyword(s):  
Thermodynamic Properties ◽  
Acoustic Waves ◽  
Subsonic Flow ◽  
Flow Direction ◽  
Noble Gas ◽  
Travelling Waves ◽  
Combustion Products ◽  
Stationary Waves ◽  
Ohmic Dissipation ◽  
Steady Current

It has been shown that in an m.h.d. generator, acoustic waves can grow due to the coupling of fluctuations in electrical conductivity, Hall parameter and thermodynamic properties of the gas, with the ohmic dissipation and electromagnetic body forces. A new analysis of this phenomenon is presented in which waves travelling at an arbitrary angle to the flow direction in a plane perpendicular to the magnetic field are considered. In contrast to McCune’s (1964) treatment the thermodynamic properties are not restricted to perfect gas laws; and the condition for spatially and temporally growing waves is examined using a general dispersion relation which includes both these types of wave. We consider in detail (i) stationary waves in supersonic flow, and (ii) travelling waves in the subsonic flow found in the G.E.G.B. 200 MW thermal input generator being built at Marchwood, and a possible power station m.h.d. generator. It is found that the waves in the 200 MW rig which burns kerosene in oxygen will be damped. But in an oil-air combustion products generator for Hall parameters of order 3 or greater, it is found that stationary waves which grow rapidly may occur at Mach numbers greater than about 1-7; and in subsonic flow waves propagating antiparallel to the steady current vector may be amplified, though the growth rate is not excessive. In noble gas m.h.d. generators these waves are more unstable than in the oil, air combustion products generator.

scholarly journals Non-local dispersion and ultrasonic tunneling in concentrationally graded solids

2019 ◽  
Vol 21 (1) ◽  
pp. 54-62
Author(s):  
A. B. Shvartsburg ◽  
M. D. Malinkovich ◽  
A. M. Kislyuk
Keyword(s):  
Acoustic Waves ◽  
Travelling Waves ◽  
Ultrasonic Waves ◽  
Formal Similarity ◽  
Constant Elasticity ◽  
Transmittance Spectra ◽  
Local Dispersion ◽  
Total Transmission ◽  
Non Local ◽  
Spectral Ranges

The non-local dispersion of longitudinal ultrasonic waves is shown to appear in the heterogeneous solids due to continuous spatial distributions of their density and/or elasticity (gradient solids). This dispersion gives rise to the diversity of ultrasonic transmittance spectra, including the broadband total reflectance plateau, total transmission and tunneling spectral ranges. The ultrasonic wave fields in gradient solids, formed by interference of forward and backward travelling waves as well as by evanescent and antievanescent modes are examined in the framework of exactly solvable models of media with continuously distributed density and elasticity. Examples of transmittance spectra for both metal and semiconductor gradient structures are presented, and the generality of concept of artificial non-local dispersion for gradient composite materials is considered. It should also be noted that the wave equation for acoustic waves in gradient media with a constant elasticity modulus and a certain predetermined density distribution reduces to an equation describing the electromagnetic wave propagation in transparent dielectric media. This formal similarity shows that the concept of nonlocal dispersion is common for both optical and acoustic phenomena, which opens the way to the direct use of physical concepts and exact mathematical solutions, developed for gradient optics, to solve the corresponding acoustic problems.

An Approximate Method to Obtain Thermodynamic Gas Properties for Use in Gas Turbines

2014 ◽  
Author(s):  
N. A. Cumpsty ◽  
A. J. Marquis
Keyword(s):  
Thermodynamic Properties ◽  
Approximate Method ◽  
Gas Turbines ◽  
Combustion Products ◽  
Empirical Approach ◽  
Polynomial Approximations ◽  
Adequate Accuracy ◽  
Computer Based ◽  
Educational Course ◽  
Gas Properties

The calculation of the performance of gas turbines, turbochargers, compressors and turbines requires the thermodynamic properties of the gases. Tables of properties exist which are effectively exact, but using these tables is tedious and far from practical in computer-based calculations. Representing tabulated results with polynomial approximations is inconvenient and prone to error in implementation. For teaching and simple calculations simple approximations, such as γ = 1.4 for unburned air and γ = 1.3 for combustion products, are sometimes used, but this is far from wholly satisfactory. This paper describes and discusses a simple empirical approach which will give adequate accuracy for many purposes but is simple enough to be used as part of an educational course.

scholarly journals Steepened Mach waves near supersonic jets: study of azimuthal structure and generation process using conditional averages

2019 ◽  
Vol 880 ◽  
pp. 594-619 ◽  
Author(s):  
Pierre Pineau ◽  
Christophe Bogey
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Flow Direction ◽  
Temporal Analysis ◽  
Wave Radiation ◽  
Flow Structures ◽  
Positive Pressure ◽  
Generation Process ◽  
Azimuthal Mode ◽  
Mach Waves

The azimuthal structure and the generation process of steepened acoustic waves are investigated in the near field of temporal round jets at Mach numbers of 2 and 3. Initially, the shear layers of the jets are in a laminar state and display instability waves whose main properties are close to those predicted from linear temporal analysis. Then, they transition to a turbulent state and generate high-intensity Mach waves displaying sharp compressions typical of those recorded for jets producing crackle noise. These waves are first shown to be poorly reproduced when only the axisymmetric mode is considered, but to be well captured with the first five azimuthal modes. Their generation process is investigated by performing conditional averages of the flow and acoustic fields triggered by the detection of intense positive pressure peak close to the jets. No steepened waves are visible in the conditionally averaged pressure profiles when the procedure involves only one azimuthal mode at a time. However, sharp compressions are obtained based on the first five modes taken together. In that case, the steep compressions are correlated over a limited portion of the jet circumference and are steeper as more azimuthal modes are considered. Moreover, a direct link is established between the steepened waves and the supersonic convection of large-scale coherent flow structures located in the supersonic core of the jets. This indicates that these waves constitute an extreme, nonlinear case of Mach wave radiation by these structures. In addition, the capacity of flow structures to generate sharp, steepened waves is related to their shapes. More particularly, flow structures with a large extent in the radial direction are shown to produce stronger and steeper Mach waves than those that are elongated in the flow direction.

Fluid flow in a tube with an elastic membrane insertion

1998 ◽  
Vol 375 ◽  
pp. 39-64 ◽  
Author(s):  
GIANNI PEDRIZZETTI
Keyword(s):  
Circular Tube ◽  
Viscous Incompressible Fluid ◽  
Travelling Waves ◽  
Finite Elasticity ◽  
Elastic Membrane ◽  
Membrane Insertion ◽  
Stationary Waves ◽  
Membrane Elasticity ◽  
Wall Interaction ◽  
Reference Pressure

The unsteady flow of a viscous incompressible fluid in a circular tube with an elastic insertion is studied numerically. The deformation of the elastic membrane is obtained by the theory of finite elasticity whose equations are solved simultaneously with the fluid equations in the axisymmetric approximation. The elastic wall expands outwards due to the positive transmural pressure and represents an idealized model for the response of pathologies in large arteries.It is found that if either the fluid discharge or the reference pressure are imposed downstream of the insertion, the fluid–wall interaction develops travelling waves along the membrane whose period depends on membrane elasticity; these are unstable in a perfectly elastic membrane and are stabilized by viscoelasticity. In the reversed system, when the fluid discharge is imposed on the opposite side, the stable propagation phenomenon remains the same because of symmetry arguments. Such arguments do not apply to the originally unstable behaviour. In this case, even when the membrane is perfectly elastic, propagation is damped and two natural fluctuations appear in the form of stationary waves. In all cases the resonance of the fluid–wall interaction has been analysed. Comparisons with previously observed phenomena and with results of analogous studies are discussed.

scholarly journals Simultaneous Single-Shot LIF-Imaging of OH and UHC in a Prevaporized, Partially Premixed, Swirl-Stabilized n-Heptane Flame

1998 ◽  
Author(s):  
Rudolf Lachner ◽  
Daniel Theisen ◽  
Rainer Fink ◽  
Dieter Rist ◽  
Achim Schmid ◽  
...  
Keyword(s):  
Flow Direction ◽  
Laser Sheet ◽  
Broad Band ◽  
Combustion Products ◽  
Single Shot ◽  
Turbulent Structures ◽  
Broad Band Emission ◽  
Band Emission ◽  
Partially Premixed ◽  
High Fluorescence

The prevaporized, partially premixed, swirl-stabilized n-heptane flame in an atmospheric pressure combustor is investigated using a tuneable KrF excimer laser. Flashing the flame with a laser sheet tuned to the P2(8) line of OH (hydroxyl radical), single-shot images of the laser-induced signals are taken simultaneously with two ICCD-cameras aligned to the same measuring volume. One camera detects mainly the laser-induced fluorescence (LIF) from the 3→2 band of the OH plus signals from UHC (unburned hydrocarbons). Only broad-band emission from UHC is imaged onto the other camera. Comparing the two images, signals stemming from OH and UHC, respectively, can be distinguished. Pictures, taken in various planes along the main flow direction, reveal highly turbulent structures in the flame. High fluorescence signals from OH can obviously be found both in filament-like flame fronts lying between fresh combustible mixtures and hot combustion products as well as in broadened reaction regions.

Thermodynamic properties of coal combustion products

2006 ◽  
Vol 53 (10) ◽  
pp. 842-847
Author(s):  
E. V. Samuilov ◽  
N. A. Sheveleva
Keyword(s):  
Thermodynamic Properties ◽  
Coal Combustion ◽  
Combustion Products ◽  
Coal Combustion Products

scholarly journals Planetary wave activity in the Arctic and Antarctic lower stratospheres during 2007 and 2008

2009 ◽  
Vol 9 (4) ◽  
pp. 14601-14643
Author(s):  
S. P. Alexander ◽  
M. G. Shepherd
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Travelling Waves ◽  
Maximum Amplitude ◽  
Wave Activity ◽  
Planetary Waves ◽  
The Arctic ◽  
Stationary Waves ◽  
Wave Amplification ◽  
Zonal Wavenumber

Abstract. Temperature data from the COSMIC GPS-RO satellite constellation are used to study planetary wave activity in both polar stratospheres from September 2006 until November 2008. One major and several minor sudden stratospheric warmings (SSWs) were recorded during the boreal winters of 2006/2007 and 2007/2008. Planetary wave morphology is studied using space-time spectral analysis while individual waves are extracted using a linear least squares fitting technique. Results show the planetary wave frequency and zonal wavenumber distribution varying between hemisphere and altitude. Most of the large Northern Hemisphere wave activity is associated with the winter SSWs, while the largest amplitude waves in the Southern Hemisphere occur during spring. Planetary wave activity during the 2006/2007 and 2007/2008 Arctic SSWs is due largely to travelling waves with zonal wavenumbers |s|=1 and |s|=2 having periods of 12, 16 and 23 days and stationary waves with |s|=1 and |s|=2. The latitudinal variation of wave amplification during the two Northern Hemisphere winters is studied. Most planetary waves show different structure and behaviour during each winter. Abrupt changes in the latitude of maximum amplitude of some planetary waves is observed co-incident in time with some of the SSWs.

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