Academic literature on the topic 'Acoustic pressure over the dynamic pressure ratio'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Acoustic pressure over the dynamic pressure ratio.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Acoustic pressure over the dynamic pressure ratio"
1
Das, R., and J. Kurian. "Supersonic flow over three dimensional cavities." Aeronautical Journal 117, no. 1188 (February 2013): 175–92. http://dx.doi.org/10.1017/s0001924000007934.
Full textAbstract:
AbstractThis work presents a study of acoustic oscillations generated and the wave structure associated with supersonic flow past wall mounted 3D open cavities of varying length-to-width (L/W) ratio. Experiments were conducted to investigate the acoustic signature generated by the cavities at freestream Mach number of 1·7. The effect ofL/Wratio of the cavity on the dominant modes of the acoustic signature registered on different walls of the cavities is investigated for anL/Wrange of 0·83-4. Shift in the dominant acoustic mode is observed asL/Wratio changes from 3 to 4. Statistical analysis of pressure data showed existence of acoustic waves and spreading of acoustic energy over different modes with change in cavity width. Time averaged schlieren visualisation indicated variation of shock and shear layer structure in the mainstream for the different cavities. Acoustic waves generated by the presence of the cavity and the dynamic behaviour of the shear layer were observed during instantaneous shadowgraph visualisation. Numerical simulation was done to make a prior assessment of the flow structure and the results are in good agreement with those from experiments. Ratio of mass exchange between cavity and mainflow and the cavity volume was observed to have profound effect on the magnitude of pressure oscillations generated by the cavities.
2
Cong, Jiqing, Jianping Jing, and Changmin Chen. "Development of a PVDF Sensor Array for Measurement of the Dynamic Pressure Field of the Blade Tip in an Axial Flow Compressor." Sensors 19, no. 6 (March 21, 2019): 1404. http://dx.doi.org/10.3390/s19061404.
Full textAbstract:
Tip clearance flow in axial flow compressor is unavoidable and responsible for pressure losses and noise generation and influences the stability of the compressor. However, necessary flow measurement in the blade tip region is a great challenge due to the small gap width as well as the structure limitation. In this paper, a polyvinylidene fluoride (PVDF) piezoelectric-film sensor array is developed to capture the dynamic pressure field over the blade tip in an axial flow compressor. The PVDF sensor array with 40 evenly distributed sensing points is fabricated directly on a 30 μm thick aluminum-metalized polarized PVDF film through photolithography. Dynamic calibration of the sensor is accomplished using acoustic source as excitation and a microphone as a reference. The test pressure range is up to 3.5 kPa and the sampling frequency is 20 kHz. The sensor presents a high signal-to-noise ratio and good consistency with the reference microphone. Sensitivity, frequency response, linearity, hysteresis, repeatability as well as the influence of temperature are also investigated through the calibration apparatus. The calibration gives credence to the relevance and reliability of this sensor for the application in dynamic pressure field measurement. The sensor is then applied to an actual measurement in a compressor. The output of the PVDF sensor array is also compared with the results of common pressure transducers, and the features of the dynamic pressure filed are discussed. The results indicate that the PVDF sensor array is capable of the dynamic pressure field measurement over the blade tip, and superior to the conventional approaches in installation, spatial resolution, frequency response, and cost. These advantages indicate its potential broad application in pressure measurement, especially for the complex spatial surface or thin-walled structure, such as the blade surface and the thin casing wall of the compressor.
3
Mosher, P., and D. W. Childs. "Theory Versus Experiment for the Effects of Pressure Ratio on the Performance of an Orifice-Compensated Hybrid Bearing." Journal of Vibration and Acoustics 120, no. 4 (October 1, 1998): 930–36. http://dx.doi.org/10.1115/1.2893922.
Full textAbstract:
This research investigates the effect of varying the concentric recess pressure ratio of hybrid (combination hydrostatic and hydrodynamic) bearings to be used in high-speed, high-pressure applications. Bearing flowrate, load capacity, torque, rotordynamic coefficients, and whirl frequency ratio are examined to determine the concentric, recess-pressure ratio which yields optimum bearing load capacity and dynamic stiffness. An analytical model, using two-dimensional bulk-flow Navier-Stokes equations and anchored by experimental test results, is used to examine bearing performance over a wide range of concentric recess pressure ratios. Typically, a concentric recess pressure ratio of 0.50 is used to obtain maximum bearing load capacity. This analysis reveals that theoretical optimum bearing performance occurs for a pressure ratio near 0.40, while experimental results indicate the optimum value to he somewhat higher than 0.45. This research demonstrates the ability to analytically investigate hybrid bearings and shows the need for more hybrid-bearing experimental data.
4
Schiavi, Alessandro, Andrea Pavoni Belli, and Francesco Russo. "Estimation of Acoustical Performance of Floating Floors from Dynamic Stiffness of Resilient Layers." Building Acoustics 12, no. 2 (June 2005): 99–113. http://dx.doi.org/10.1260/1351010054037938.
Full textAbstract:
This paper describes a procedure for evaluating the reduction in impact sound pressure level of floating floors by measuring the apparent dynamic stiffness of the resilient layer, according to International Standard EN 29052-1. The impact sound pressure level experimental data, obtained according to International Standard UNI EN ISO 140-8, was compared with estimates obtained from dynamic stiffness measurements. Results confirm the effectiveness of the empirical model. Two questions are addressed. The first concerns the decrease in layer thickness over time. The second concerns the relationship between damping ratio and performance.
5
Sugimoto, N. "Nonlinear theory for thermoacoustic waves in a narrow channel and pore subject to a temperature gradient." Journal of Fluid Mechanics 797 (May 26, 2016): 765–801. http://dx.doi.org/10.1017/jfm.2016.295.
Full textAbstract:
A nonlinear theory for thermoacoustic waves in a gas-filled, narrow channel and pore subject to an axial temperature gradient is developed based on the fluid dynamical equations for an ideal gas. Under the narrow-tube approximation, three small parameters are introduced as asymptotic parameters, one being the ratio of a span length to a typical thickness of the thermoviscous diffusion layer, another the ratio of the typical propagation speed of thermoacoustic waves to an adiabatic sound speed and the final parameter is the ratio of the typical magnitude of a pressure disturbance to uniform pressure in a quiescent state. No thermal interaction between the gas and the solid wall is taken into account on assuming that the wall has a large heat capacity. Using the three small parameters, the fluid dynamical equations are approximated asymptotically to be reduced to a single nonlinear diffusion wave (advection) equation for an excess pressure. All field variables are determined consistently in terms of the excess pressure so as to satisfy the boundary conditions on the wall. Supposing a time-periodic solution to the equation derived, the mean value of the excess pressure over one period is examined. It is shown that while the mean vanishes in the linear theory, it decreases monotonically due to nonlinearity. It is also shown that mean values of the shear stress and the heat flux at the wall, as well as those of the vector fields of the mass and energy fluxes representing, respectively, acoustic and thermoacoustic streaming, are expressed in terms of the mean values of the products of the spatial and/or temporal pressure gradients, which are reduced to the spatial derivatives of the mean pressure.
6
Chorpening, B. T., J. D. Thornton, E. D. Huckaby, and K. J. Benson. "Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor." Journal of Engineering for Gas Turbines and Power 129, no. 2 (August 30, 2006): 352–57. http://dx.doi.org/10.1115/1.2431390.
Full textAbstract:
To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented that operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blow off, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25m∕s(82ft∕s). The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.
7
Wagner, Justin L., Steven J. Beresh, Katya M. Casper, Edward P. DeMauro, and Srinivasan Arunajatesan. "Resonance dynamics in compressible cavity flows using time-resolved velocity and surface pressure fields." Journal of Fluid Mechanics 830 (October 2, 2017): 494–527. http://dx.doi.org/10.1017/jfm.2017.606.
Full textAbstract:
The resonance modes in Mach 0.94 turbulent flow over a cavity having a length-to-depth ratio of five were explored using time-resolved particle image velocimetry (TR-PIV) and time-resolved pressure sensitive paint (TR-PSP). Mode switching was quantified in the velocity field simultaneous with the pressure field. As the mode number increased from one through three, the resonance activity moved from a region downstream within the recirculation region to areas further upstream in the shear layer, an observation consistent with linear stability analysis. The second and third modes contained organized structures associated with shear layer vortices. Coherent structures occurring in the velocity field during modes two and three exhibited a clear modulation in size with streamwise distance. The streamwise periodicity was attributable to the interference of downstream-propagating vortical disturbances with upstream-travelling acoustic waves. The coherent structure oscillations were approximately $180^{\circ }$ out of phase with the modal surface pressure fluctuations, analogous to a standing wave. Modal propagation (or phase) velocities, based on cross-correlations of bandpass-filtered velocity fields were found for each mode. The phase velocities also showed streamwise periodicity and were greatest at regions of maximum constructive interference where coherent structures were the largest. Overall, the phase velocities increased with modal frequency, which coincided with the modal activity residing at higher portions of the cavity where the local mean flow velocity was elevated. Together, the TR-PIV and TR-PSP provide unique details not only on the distribution of modal activity throughout the cavity, but also new understanding of the resonance mechanism as observed in the velocity field.
8
Hileman, J., and M. Samimy. "Effects of Vortex Generating Tabs on Noise Sources in an Ideally Expanded Mach 1.3 Jet." International Journal of Aeroacoustics 2, no. 1 (January 2003): 35–63. http://dx.doi.org/10.1260/147547203322436935.
Full textAbstract:
The flow and acoustic fields of an ideally expanded Mach 1.3 axisymmetric jet with delta tabs were examined to explore the effects of the tabs on noise sources. This work continues research that was performed on a baseline (no-tab) jet. Noise measurements were made at an angle of 30° to the downstream jet axis to allow a direct comparison to previous work, and to relate the sound generation mechanisms to the large structures that were visualized with temporally resolved flow visualization. Additional acoustic measurements were made at 60° and 90° locations. Three cases were examined: a baseline jet, a single delta tab jet, and a dual delta tab jet. Both tab jets were operated at the same pressure ratio as the baseline jet, which was ideally expanded. Power spectra and average acoustic waveform measurements were made for a variety of azimuthal locations; apparent noise origins were estimated with a 3-D microphone array; and temporally resolved flow visualization was used to examine the dynamic flow structure of the jet's mixing-layer. The results confirm that the tabs generate strong streamwise vortices that have a significant effect on both the flow and acoustic fields of the jet. The tabs cause significant deformation in the cross-stream plane of the mixing-layer, as well as regulating the formation and roll-up of vortices due to Kelvin Helmholtz instability. With the addition of tabs, the noise field becomes azimuthally dependent and the region of noise generation moves dramatically upstream. It appears that the tabs are directly responsible for an increase in noise over a range of Strouhal numbers between 0.8 and 2.5 through generated streamwise vortices and they are indirectly responsible for the modification of the noise generating mechanisms at Strouhal numbers below 0.6 through the induced spanwise vortex roll-ups.
9
Yurikov, Alexey, Roman Pevzner, Konstantin Tertyshnikov, Vassily Mikhaltsevitch, Boris Gurevich, and Maxim Lebedev. "Laboratory measurements with DAS: A fast and sensitive tool to obtain elastic properties at seismic frequencies." Leading Edge 40, no. 9 (September 2021): 655–61. http://dx.doi.org/10.1190/tle40090655.1.
Full textAbstract:
Forced-oscillation stress-strain laboratory measurements are increasingly employed to obtain elastic and viscoelastic properties of rocks at seismic frequencies. Yet these measurements are time-consuming and expensive, due in part to the use of metal or semiconductor strain gauges, which need to be glued to the sample. Such gauges are fragile, have relatively low sensitivity, and measure very local strain only so the measurements can be affected by a slight misalignment of the system assembly and local heterogeneity of the rock. The emergence of fiber-optic distributed acoustic sensing (DAS) technology provides an alternative means of measuring strain. Strain measurements with DAS involve winding an optical fiber around the sample multiple times and connecting it to a DAS recording unit. Pilot experiments performed using this setup on a range of rocks and materials show good agreement with strain gauge measurements. Advantages of DAS over strain gauges include much higher strain sensitivity (down to 10−11) and signal-to-noise ratio (and hence, shorter time required for measurements), larger dynamic range, ability to measure average (rather than local) strain in the sample, and robustness at elevated temperatures. Although the pilot experiments demonstrate the potential of DAS for rock physics measurements, further research and improvement of the proposed methodology are required to obtain independent estimates of Young's modulus and Poisson's ratio and to port the system into a pressure vessel to obtain rock properties under in-situ conditions.
10
Abderrahmane, Belkallouche, Tahar Rezoug, and Laurent Dala. "Passive control of cavity acoustics via the use of surface waviness at subsonic flow." Aircraft Engineering and Aerospace Technology 91, no. 2 (February 4, 2019): 296–308. http://dx.doi.org/10.1108/aeat-01-2018-0061.
Full textAbstract:
PurposeAircraft noise is dominant for residents near airports when planes fly at low altitudes such as during departure and landing. Flaps, wings, landing gear contribute significantly to the total sound emission. This paper aims to present a passive flow control (in the sense that there is no power input) to reduce the noise radiation induced by the flow over the cavity of the landing gear during take-off and landing.Design/methodology/approachThe understanding of the noise source mechanism is normally caused by the unsteady interactions between the cavity surface and the turbulent flows as well as some studies that have shown tonal noise because of cavity resonances; this tonal noise is dependent on cavity geometry and incoming flow that lead us to use of a sinusoidal surface modification application upstream of a cavity as a passive acoustics control device in approach conditions.FindingsIt is demonstrated that the proposed surface waviness showed a potential reduction in cavity resonance and in the overall sound pressure level at the majority of the points investigated in the low Mach number. Furthermore, optimum sinusoidal amplitude and frequency were determined by the means of a two-dimensional computational fluid dynamics analysis for a cavity with a length to depth ratio of four.Research limitations/implicationsThe noise control by surface waviness has not implemented in real flight test yet, as all the tests are conducted in the credible numerical simulation.Practical implicationsThe application of passive control method on the cavity requires a global aerodynamic study of the air frame is a matter of ongoing debate between aerodynamicists and acousticians. The latter is aimed at the reduction of the noise, whereas the former fears a corruption of flow conditions. To balance aerodynamic performance and acoustics, the use of the surface waviness in cavity leading edge is the most optimal solution.Social implicationsThe proposed leading-edge modification it has important theoretical basis and reference value for engineering application it can meet the demands of engineering practice. Particularly, to contribute to the reduce the aircraft noise adopted by the “European Visions 2020”.Originality/valueThe investigate cavity noise with and without surface waviness generation and propagation by using a hybrid approach, the computation of flow based on the large-eddy simulation method, is decoupled from the computation of sound, which can be performed during a post-processing based on Curle’s acoustic analogy as implemented in OpenFOAM.
Dissertations / Theses on the topic "Acoustic pressure over the dynamic pressure ratio"
1
Coltrin, Ian S. "The Influence of Nozzle Spacing and Diameter on the Acoustic Emissions of Closely Spaced Supersonic Jet Arrays." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/2935.
Full textAbstract:
The acoustic emissions from supersonic jets represent an area of significant research needs; not only in the field of aero-acoustics, but in industry as well where high pressure let down processes have been known to cause acoustically induced vibrations. A common method to reduce the acoustic emissions of such processes involves dividing the single larger supersonic flow into several smaller ones. Though this is common practice, there is not yet a current model which describes the reduction of acoustic emissions from an array of smaller supersonic jets. Current research which studies supersonic jet arrays are mainly focused on the effects of screech. Though screech is important, due to its high amplitude acoustic pressure, this research focuses on the overall acoustic emissions radiated from supersonic jet arrays which can cause severe acoustic loadings. This research investigated the acoustic emissions and shock formations from several eight by eight arrays of axisymmetric jet experimentally. The array nozzle diameters investigated ranged from 1/8 inch to 1/4 inch and the spacing over diameter ratio ranged from 1.44 to 3. The net pressure ratios investigated ranged from 2 to 24. Results revealed a strong correlation between the acoustic emissions and the shock formations of the flow. Up until a critical net pressure ratio, the overall sound pressure levels were comparable to that of a single jet within an array. At net pressure ratios beyond the critical the overall sound pressure levels transitioned to higher decibel levels; equivalent to a single jet with an equivalent exit area of an entire array. Also, the characteristic acoustic frequency emitted from a nozzle array remained ultrasonic (above 20 kHz) at lower net pressure ratios and then shifted to audible levels (between 20 Hz to 20 kHz) at net pressure ratios beyond the critical. Also, before the critical net pressure ratio the shock cells from the jets within the array remained unmerged, but at net pressure ratios beyond the critical the shock cells merged and formed lattices of weak oblique shocks at first and then strong oblique shocks as the net pressure ratio continued to increase. The critical net pressure ratio was investigated by non-dimensional analysis. The non-dimensional analysis revealed that the critical net pressure ratio was a strong linear function of the spacing over diameter ratio. A linear model was derived which is able to predict the critical net pressure ratio, and in turn, predict a critical shift in the acoustic emissions of a nozzle array.
Conference papers on the topic "Acoustic pressure over the dynamic pressure ratio"
1
Mohany, Atef, and Samir Ziada. "Effect of Acoustic Resonance on the Dynamic Lift Forces Acting on Two Tandem Cylinders in Cross-Flow." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93086.
Full textAbstract:
Direct measurement of the dynamic lift force for the case of two tandem cylinders in cross-flow during acoustic resonance is performed. Two spacing ratios inside the proximity interference region, L/D = 2.5 and 3, are considered. During the tests, the acoustic transverse-modes of the duct housing the cylinder are self-excited. In the absence of acoustic resonance, the measured dynamic lift coefficient agrees well with those reported in the literature. When the acoustic resonance is initiated, a drastic increase in the dynamic lift coefficient is observed, especially on the downstream cylinder. This is associated with abrupt changes in the phase between the lift forces and the acoustic pressure. The dynamic lift forces on both cylinders are also decomposed into in-phase and out-of-phase components, with respect to the resonant sound pressure. The lift force components for the downstream cylinder are found to be dominant. Moreover, the out-of-phase component of the lift force on the downstream cylinder is found to become negative over two different ranges of flow velocity and to virtually vanish between these two ranges. Acoustic resonance is therefore generated over two ranges of reduced velocity separated by a non-resonant range near the velocity of frequency coincidence. The out-of-phase lift component of the downstream cylinder is found to control the occurrence of acoustic resonance, whereas the in-phase lift component seems to cause slight variations in the acoustic resonance frequency.
2
Bozak, Richard F. "Measurements of Multiple Pure Tone Propagation From a High Bypass Turbofan Rotor in an Internal Flow Facility." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14161.
Full textAbstract:
Abstract An important noise source in modern high bypass ratio turbofans is from multiple pure tones produced by the fan during takeoff. An experiment conducted on a 1.5 pressure ratio fan in an internal flow facility provided dynamic pressure measurements to investigate multiple pure tone generation and propagation. Since multiple pure tones are generated by blade shock variation primarily due to the fan’s blade stagger angle differences, the blade stagger angles were measured with an array of over-the-rotor dynamic pressure transducers. Multiple pure tone measurements were made with 30 wall-mounted dynamic pressure transducers from 0.4 to 1.1 diameters upstream of the rotor. Measured blade stagger angle differences correspond to the the shock amplitude variation measured upstream. The acoustic field was extracted from the dynamic pressure signals using principal component analysis as well as duct mode beamforming. Shocks traveling out the inlet were found to couple to duct modes propagating at similar angles. Over-the-rotor acoustic liners appear to reduce rotor shock variation resulting in a reduction of sub-harmonic multiple pure tone sound pressure levels by 3–4 dB.
3
Lee, Hyung Ju, Kyu Tae Kim, Jong Guen Lee, Bryan D. Quay, and Domenic A. Santavicca. "An Experimental Study on the Coupling of Combustion Instability Mechanisms in a Lean Premixed Gas Turbine Combustor." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-60009.
Full textAbstract:
An experimental study was conducted to characterize the combined effects of flame-vortex interactions and equivalence ratio fluctuations on self-excited combustion instabilities in a swirl-stabilized lean premixed gas turbine combustor. The combustor was designed so that the fuel injector location and the combustion chamber length could be independently varied. In addition, the fuel and air could be mixed upstream of the choked inlet to the combustor, thereby eliminating the possibility of equivalence ratio fluctuations. Experiments were performed over a broad range of operating conditions and at each condition both the combustor length and the fuel injection location were varied. Dynamic pressure in the combustor, acoustic pressure and velocity in the mixing section, and the overall rate of heat release were simultaneously measured at all operating conditions. Two distinct instability regimes were observed; one near 220 Hz and the other near 345 Hz. It was also found that the strength of the instability changed significantly as the fuel injection location was varied, while the phase of the acoustic pressure and velocity fluctuations in the mixing section did not change. A time series of pressure and CH* chemiluminescence signals confirmed constructive or destructive coupling of the two instability mechanisms; the flame-vortex interaction and the equivalence ratio fluctuation interact each other and determine the instability characteristics in partially premixed conditions.
4
Edmonds, Ryan G., Robert C. Steele, Joseph T. Williams, Douglas L. Straub, Kent H. Casleton, and Avtar Bining. "Ultra-Low NOx Advanced Vortex Combustor." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90319.
Full textAbstract:
An ultra lean-premixed Advanced Vortex Combustor (AVC) has been developed and tested. The natural gas fueled AVC was tested at the U.S. Department of Energy’s National Energy Technology Laboratory (USDOE NETL) test facility in Morgantown (WV). All testing was performed at elevated pressures and inlet temperatures and at lean fuel-air ratios representative of industrial gas turbines. The improved AVC design exhibited simultaneous NOx/CO/UHC emissions of 4/4/0 ppmv (all emissions are at 15% O2 dry). The design also achieved less than 3 ppmv NOx with combustion efficiencies in excess of 99.5%. The design demonstrated tremendous acoustic dynamic stability over a wide range of operating conditions which potentially makes this approach significantly more attractive than other lean premixed combustion approaches. In addition, a pressure drop of 1.75% was measured which is significantly lower than conventional gas turbine combustors. Potentially, this lower pressure drop characteristic of the AVC concept translates into overall gas turbine cycle efficiency improvements of up to one full percentage point. The relatively high velocities and low pressure drops achievable with this technology make the AVC approach an attractive alternative for syngas fuel applications.
5
Prieur, Kevin, Daniel Durox, Thierry Schuller, and Sébastien Candel. "Strong Azimuthal Combustion Instabilities in a Spray Annular Chamber With Intermittent Partial Blow-Off." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63343.
Full textAbstract:
The present article reports original experiments carried out in the MICCA-Spray combustor developed at EM2C, CNRS and CentraleSupélec. This system comprises 16 swirl spray injectors. Liquid n-heptane is injected by hollow cone simplex atomizers. The combustion chamber is formed by two cylindrical quartz tubes allowing full optical access to the flame region and it is equipped with eight pressure sensors recording signals in the plenum and chamber. A high speed camera provides images of the flames and photomultipliers record the light intensity from different flames. For certain operating conditions, the system exhibits well defined instabilities coupled by the first azimuthal mode of the chamber at a frequency of about 750 Hz. These instabilities occur in the form of bursts with a moderate level of growth. Examination of the pressure and the light intensity signals gives access to the acoustic energy source term. Analysis of the phase between the two signals during the instability bursts (growth, limit cycle, decay) is carried out using cross-spectral analysis. At limit cycle, large amplitude of pressure oscillations are reached with peak values around 5000 Pa (or 5% of the mean pressure in the chamber), and these levels persist over a finite period of time. Detailed analysis of the signals using the spin ratio indicates that the standing mode is predominant. The chamber can exhibit a spinning mode but with a lower amplitude of acoustic fluctuation. Analysis of the flame dynamics at the pressure anti-nodal line reveals a strong longitudinal pulsation with heat release rate oscillations in phase and increasing linearly with the acoustic pressure even at the highest oscillation levels. At the pressure nodal line, the flames are subjected to large transverse velocity fluctuations leading to a transverse motion of the flames and partial blow-off. Scenarios and modeling elements are developed to interpret these features. To the best of our knowledge, this is the first time that azimuthal instabilities are characterized in a well-controlled annular combustor with swirled spray flames.
6
Chorpening, B. T., J. D. Thornton, E. D. Huckaby, and K. J. Benson. "Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53881.
Full textAbstract:
To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented which operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blowoff, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25 m/s. The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.
7
Straub, Douglas L., and Geo A. Richards. "Effect of Fuel Nozzle Configuration on Premix Combustion Dynamics." In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-492.
Full textAbstract:
Combustion dynamics (or combustion oscillations) have emerged as a significant consideration in the development of low-emission gas turbines. To date, the effect of premix fuel nozzle geometry on combustion dynamics has not been well-documented. This paper presents experimental stability data from several different fuel nozzle geometries (i.e., changing the axial position of fuel injection in the premixer, and considering simultaneous injection from two axial positions). Tests are conducted in a can-style combustor designed specifically to study combustion dynamics. The operating pressure is fixed at 7.5 atmospheres and the inlet air temperature is fixed at 588K (600F). Tests are conducted with a nominal heat input of 1MWth (3MBTUH). Equivalence ratio and nozzle reference velocity are varied over the ranges typical of premix combustor design. The fuel is natural gas. Results show that observed dynamics can be understood from a time-lag model for oscillations, but the presence of multiple acoustic modes in this combustor makes it difficult to achieve stable combustion by simply re-locating the point of fuel injection. In contrast, reduced oscillating pressure amplitude was observed at most test conditions using simultaneous fuel injection from two axial positions.
8
Whitlow, Jesse W., and Robert P. Tomko. "Tongue and Groove Joint Stability Testing in Air." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37245.
Full textAbstract:
Dynamic and static stability testing was performed on a tongue-in-groove joint using air as the driving fluid. The testing was performed to evaluate the conditions that would produce oscillations that could result in sustained vibration of the test piece (dynamic instability) and to determine the conditions for which the joint would seal (static instability). The key variables that were adjusted in the test were the length of the gap, the width of the gap, and the position of the tongue within the groove. Four test configurations were evaluated with different gap widths and engagement lengths to produce L/go (tongue engagement length to groove gap width) ratios ranging from 1.2 to 42. The smallest L/go configuration, which was the most dynamically unstable configuration, was repeated with damping added to the spring-mass system. Each configuration was flow tested over a range of differential pressures and disk positions within the groove. Differential pressure, disk position, displacement due to disk vibration, disk acceleration, flow through the gap, and acoustic pressure in the gap were measured and recorded. Testing showed the most violent unstable behavior occurs when the disk is centered in the groove, while the behavior tends to be stable when the disk is near the downstream sealing surface of the groove.
9
Kim, Kyu Tae, Karthik Kashinath, and Simone Hochgreb. "Effects of Nonuniform Reactant Stoichiometry on Combustion Instability." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45097.
Full textAbstract:
This paper analyzes the forced response of swirl-stabilized lean-premixed flames to acoustic forcing in a laboratory-scale stratified burner. The double-swirler, double-channel annular burner was specially designed to generate acoustic velocity oscillations and radial fuel stratification at the inlet of the combustion chamber. Temporal oscillations of equivalence ratio along the axial direction are dissipated over a long distance, and therefore the effects of time-varying fuel/air ratio on the flame response are not considered. Simultaneous measurements of inlet velocity and heat release rate oscillations were made using a hot wire anemometer and photomultiplier tubes with narrowband OH*/CH* interference filters. Time-averaged CH* chemiluminescence intensities were measured using an intensified CCD camera. Results show that flame stabilization mechanisms vary depending on stratification ratio for a constant global equivalence ratio. For a uniformly premixed condition, an enveloped M-shaped flame is observed. For stratified conditions, however, a dihedral V-flame and a detached flame are developed for outer stream and inner stream fuel enrichment cases, respectively. Flame transfer function (FTF) measurement results indicate that a V-shaped flame tends to damp incident flow oscillations, while a detached flame acts as a strong amplifier relative to the uniformly premixed condition. The phase difference of FTF increases in the presence of stratification. More importantly, the dynamic characteristics obtained from the forced stratified flame measurements are well correlated with unsteady flame behavior under limit-cycle pressure oscillations. The results presented in this paper provide insight into the impact of nonuniform reactant stoichiometry on combustion instabilities, which has not been well explored to date.
10
Tuncer, Onur, Sumanta Acharya, and Jong Ho Uhm. "Effects of Hydrogen Enrichment on Confined Methane Flame Behavior." In ASME 2006 Power Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/power2006-88079.
Full textAbstract:
Many land based power generation units presently operate on natural gas, whose major constituent is methane, and many of them would need to tackle the challenges due to a fuel switch towards synthesis gas in the near future. Operating conditions and stability of a pre-mixed gas turbine combustor is quite sensitive to the changes in the fuel composition. Behavior of a premixed confined hydrogen enriched methane flame is studied with regard to thermo-acoustic instability induced flame flashback, emissions, flammability limits and acoustics over a wide range of operating conditions. However, most emphasis is put on lean combustion, which is an industry standard method used to lower pollutant emissions by reducing adiabatic flame temperatures. Hydrogen addition extends the flammability limits and enables lower nitric oxide emissions levels to be achieved at leaner equivalence ratios. On the other hand, increased root-mean-square pressure fluctuation levels, and higher susceptibility to flashback is observed with increasing hydrogen volume fraction inside the fuel mixture. This phenomenon is mostly attributed to much higher burning speeds of hydrogen in contrast to pure methane. A semi-analytical model has been utilized to capture the flame holding and thermo-acoustically induced flame flashback dynamics for a pre-mixed gas turbine combustor. A simple linearized acoustic model, derived from the basic conservation laws, and a front-tracking algorithm based on the Markstein’s G-equation are coupled together in order to track the flame initiation front, which in turn yields in an understanding of dynamic flame holding characteristics. A limit cycle behavior in the flame front movement is observed during simulations due to a non-linearity in the feedback term that relates acoustic velocity to heat release. Sets of experiments including flashback speed measurements have been performed at varying fuel composition. Phase locked CH radical imaging measurements have also been performed in order to track the flame initiation front in time with respect to the dominant instability cycle. Computer simulations are performed to study flashback and combustor acoustics together numerically and it is observed that these are in good qualitative agreement with the experiments.