Academic literature on the topic 'Controlled nozzle oscillation'
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Journal articles on the topic "Controlled nozzle oscillation"
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Wang, Jun, and S. Xu. "Enhancing the AWJ Cutting Performance by Multipass Machining with Controlled Nozzle Oscillation." Key Engineering Materials 291-292 (August 2005): 453–58. http://dx.doi.org/10.4028/www.scientific.net/kem.291-292.453.
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The cutting performance in abrasive waterjet (AWJ) multipass cutting with and without controlled nozzle oscillation is presented based on an experimental investigation cutting an 87% alumina ceramic. The cutting capacity in terms of the depth of cut and the kerf geometrical features is analyzed with respect to the process variables. It is found that multipass cutting is a viable means to increase the cutting performance and application domain of this technology, while a further increase in the cutting performance can be made by using a controlled nozzle oscillation technique.
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Chen, F. L., E. Siores, and K. Patel. "Improving the cut surface qualities using different controlled nozzle oscillation techniques." International Journal of Machine Tools and Manufacture 42, no. 6 (May 2002): 717–22. http://dx.doi.org/10.1016/s0890-6955(01)00161-4.
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Xu, S., and J. Wang. "A study of abrasive waterjet cutting of alumina ceramics with controlled nozzle oscillation." International Journal of Advanced Manufacturing Technology 27, no. 7-8 (February 23, 2005): 693–702. http://dx.doi.org/10.1007/s00170-004-2256-7.
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Wang, Jun. "A Focused Review on Enhancing the Abrasive Waterjet Cutting Performance by Using Controlled Nozzle Oscillation." Key Engineering Materials 404 (January 2009): 33–44. http://dx.doi.org/10.4028/www.scientific.net/kem.404.33.
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Increasing the performance of the abrasive waterjet (AWJ) cutting technology for engineering materials is the ultimate aim of research in this field. This paper presents a review on the studies using a controlled nozzle oscillation technique to increase the cutting performance of the AWJ cutting technology and the associated mechanisms primarily based on the work in the author’s laboratory. Primary attention is paid to the discussions of the depth of cut, the effect and selection of process parameters and the advantages by using this technique in both single- and multi-pass cutting modes.
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Samanta, Arnab, S. Narayanan, Shailesh Kumar Jha, and Ashish Narayan. "Numerical simulation of a sonic-underexpanded jet impinging on a partially covered cylindrical Hartmann whistle." SIMULATION 94, no. 8 (November 17, 2017): 707–21. http://dx.doi.org/10.1177/0037549717741202.
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The present study numerically investigates the effect of a partially covered cylindrical shield on the flow/shock oscillation characteristics of a Hartmann whistle when the pulsating jet exits through the two small openings, (a) close to the cavity inlet, and (b) away from the cavity inlet, of the cylindrical shield. The relevant parameters that modify the flow/shock oscillations of the Hartmann whistle are the stand-off distance, nozzle pressure ratio, cavity length, cavity shield, jet diameter, etc. The pulsating nature of flow in a partially shielded Hartmann whistle is investigated for various stand-off distances to understand its effect in achieving effective flow control. The velocity vectors indicate that the partly shielded Hartmann whistle operates in the jet regurgitant mode with different regurgitant phases. It also shows that some amount of the jet near the cavity inlet gets diverted towards the shield and gets attached to it, whereas some exits out through the two shield openings which can be injected into the flow to be controlled. The Mach number contours indicate the flow deceleration/reacceleration zones, shock-cell structures as well as fluid column oscillations in shock-cells/cavity regions. The present study reveals that the stand-off distance and the jet diameter are the crucial parameters, which control the oscillation mechanisms in a partially covered Hartmann whistle for achieving effective flow control. Thus, this paper sufficiently demonstrates the role of stand-off distances, openings in the shield as well as jet diameter in modifying the flow/shock oscillation characteristics of a partially shielded Hartmann whistle in achieving the finest flow control.
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Maruthupandiyan, K., and E. Rathakrishnan. "Supersonic jet control with shifted tabs." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 232, no. 3 (November 25, 2016): 433–47. http://dx.doi.org/10.1177/0954410016679197.
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Mixing characteristics of a Mach 2 jet controlled by shifted tabs have been studied at different levels of expansion at the nozzle exit. Two identical rectangular flat tabs of aspect ratios (length/width) 3, 4, 5 and 6, offering 2.5% blockage each, located diametrically opposite, found that the mixing promotion caused by the shifted tab increases with increase of adverse pressure gradient (that is, below NPR 5). On the contrary, the mixing enhancement caused by tab placed at the nozzle exit decreases with increase of adverse pressure gradient. At higher NPRs from 5 to 8 for shifted tab configuration, the amplitude of centerline pitot pressure oscillation is considerably smaller than the uncontrolled jet. At lower NPRs, corresponding to expansion level pe /pa, from 0.383 to 0.511, shifted tab is found to be a better mixing promoter than the tab at the nozzle exit. But for expansion levels from 0.511 to 1.022, mixing promoted by tab at nozzle exit is better than the shifted tabs. Shifted tab at 0.5D results in about 55% reduction in core length, at NPR 3, and the corresponding core length reduction by tabs at 0.25D, 0.5D, and 0D is 25.93%, 22.2%, and 14.81%, respectively.
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Ansari, A. R., and A. R. B. Novinzadeh. "Designing a Control System for an Airplane Wing Flutter Employing Gas Actuators." International Journal of Aerospace Engineering 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/4209619.
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The wing flutter is a dynamic instability of a flight vehicle associated with the interaction of aerodynamic, elastic, and inertial forces (aeroelastics phenomena). In this study, just the primary control is investigated. Also, in order to control the two-dimensional wing flutter, the force jet and pulse width pulse frequency (PWPF) are suggested. The PWPF modulator has the advantage of almost linear operation, low jet gas consumption, flexibility in addressing various needs, and good accuracy in presence of oscillations. This scheme makes use of quasi-steady dynamic premises and incompressible flow, as well as the thin airfoil theory. It should be noted that, to justify the application of the aerodynamic theory, we have speculated that the thruster jet ejected through a nozzle with a diameter smaller than several millimeters has a supersonic regime (with Mach number of the order of M≈3.5). Consequently, the interference of the thruster jet in the boundary layer, flow, and circulation around the airfoil which are characterized by low speed would be negligible. The operation of the jet as a thruster is handled by the PWPF modulator, and the process output is fed back to the system via a PD controller. In order to control the wing flutter oscillation, the location of installing the actuator on the airfoil is investigated.
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Akbarzadeh, M., and M. J. Kermani. "NUMERICAL SIMULATIONS OF INVISCID AIRFLOWS IN RAMJET INLETS." Transactions of the Canadian Society for Mechanical Engineering 33, no. 2 (June 2009): 271–96. http://dx.doi.org/10.1139/tcsme-2009-0021.
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The performances of three different ramjet inlets and an entire ramjet are numerically studied in this paper. The fluid is assumed to be inviscid. Inlet 1 is a SCRAMJET inlet and is chosen from the literature. Inlets 2 and 3 are instead designed based on the Oswatitsch principle. Inlets 2 and 3 produce a series of oblique shocks merging at the engine cowl lip followed by a terminating normal shock just downstream of the inlet throat. In ramjet, the combustion is modeled using a non-uniform volumetric heat source distributed in the combustor area. The position of the terminating normal shock in Inlets 2 and 3 is controlled via the inlet’s back pressure. Instead, in ramjet it is bounded by the amount of heat rate added in combustor and the exhaust nozzle throat area. For the numerical simulations, the Roe (1981) and MacCormack (1969) schemes are used. To prevent the spurious numerical oscillations in high resolution computations by Roe scheme the van Albada flux limiter (1982) is used, while in MacCormack scheme artificial viscosity terms are added to damp the oscillations. To double check the accuracy of the computations, the Fluent software package has also been used. Comparisons show very good agreement.
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Raman, G., S. Packiarajan, G. Papadopoulos, C. Weissman, and S. Raghu. "Jet thrust vectoring using a miniature fluidic oscillator." Aeronautical Journal 109, no. 1093 (March 2005): 129–38. http://dx.doi.org/10.1017/s0001924000000634.
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Abstract This paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass addition. The fluidic actuators used had no moving parts and produced oscillatory flow with a square wave form at frequencies up to 1·6kHz. A subsonic jet with an exit diameter of 3·81cm was controlled using single and dual fluidic actuators, each with an equivalent circular diameter of 1·06mm. The fluidic nozzle was operated at pressures between 20·68 and 165·47kPa. The objectives of the present work included documentation of the actuation characteristics of fluidic devices, assessment of the effectiveness of fluidic devices for jet thrust vectoring, and evaluation of mass flow requirements for vectoring under various conditions. Measurements were made in the flow field using a pitot probe for the vectored and unvectored cases. Some acoustic measurements were made using microphones in the near-field and for selected cases particle image velocimetry (PIV) measurements were made. Thrust vectoring was obtained in low speed jets by momentum effects with fluidic device mass flow rates of only 2 × 10–4kg/sec (0·6% of main jet mass flow per fluidic oscillator). Although a single fluidic device produced vectoring of the primary jet, the dual fluidic device configuration (with two fluidic devices on either side of the jet exit) produced mass flux enhancement of 28% with no vectoring. Our results indicate that fluidic actuators have the potential for use in thrust vectoring, flow mixing and industrial flow deflection applications.
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Алексеев, Геннадий, Gennadii Alekseev, Ольга Егорова, Olga Egorova, Дмитрий Молдованов, Dmitrii Moldovanov, Алексей Егоров, and Aleksey Egorov. "Spray Drying of Food Suspensions: Upgrading Capabilities." Food Processing: Techniques and Technology 49, no. 1 (June 26, 2019): 70–76. http://dx.doi.org/10.21603/2074-9414-2019-1-70-76.
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Spray drying is currently used to obtain powder products from suspensions. It is considered the most effective type of drying for such media. The complexity of the drying process is associated with thermal destruction of components, which degrades the properties of the product and imposes significant restrictions on temperature condition. The present research features the simulation of transient modes of operation of the solenoids to generate a controlled cavitation effect when applied to a stream of acoustic vibrations using a magnetostrictive generator of ultrasound. The authors propose a new design of spray nozzle for drying suspensions with counter-connected solenoids. Such solenoids can cause deformation of the main suspension supply line. The intensity of the cavitation processes depends on the dynamics of the solenoid actuation. The paper introduces a mathematical modeling of transient modes of operation for ultrasonic frequency generator solenoids that create a controlled cavitation effect when applied to the jet of acoustic oscillations of this frequency. When modeling the process of operation of solenoids, the main criterion for changing the intensity of cavitation is the average rate of change in the volume of the cavity at the stage of its collapse, related to one cycle of oscillations for a spherical cavity. An increase in the static pressure of the liquid led to a shift in the phase of the collapse of the cavity. As a result of the chosen mathematical model, a numerical experiment with modeling in the MathCAD program was carried out. It revealed some graphical dependences of the change in U(t), L(t), and R(t). The obtained data allow one to predict the ballast induction and active load (R, L) for the control of transients in the solenoid of the ultrasonic generator. These dependences make it possible to choose more effective parameters for drying suspensions, which is especially important for heat- sensitive components.
Dissertations / Theses on the topic "Controlled nozzle oscillation"
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Alexan, Karim Carleton University Dissertation Engineering Aeronautical. "Controlled oscillation of forebody vortices by nozzle jet blowing." Ottawa, 1992.
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Zhong, Yu Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "A study of the cutting performance in multipass abrasive waterjet machining of alumina ceramics with controlled nozzle oscillation." Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/41216.
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An experimental investigation has been undertaken to study the depth of cut in multipass abrasive waterjet (AWJ) cutting of an 87% alumina ceramic with controlled nozzle oscillation. The experimental data have been statistically analysed to study the trends of the depth of cut with respect to the process parameters. It has been found that multipass cutting with controlled nozzle oscillation can significantly increase the depth of cut. Within the same cutting time and using the same cutting parameters other than the jet traverse speed, it has been found that multipass cutting with nozzle oscillation can increase the depth of cut by an average of 74.6% as compared to single pass cutting without nozzle oscillation. Furthermore, a multipass cutting with higher nozzle traverse speeds can achieve a larger depth of cut than a single pass cutting at a low traverse speed within the same cutting time. A recommendation has been made for the selection of appropriate process parameters for multipass cutting with nozzle oscillation. In order to estimate the depth of cut on a mathematical basis, predictive models for the depth of cut in multipass cutting with and without nozzle oscillation have been developed using a dimensional analysis technique. The model development starts with the models for single pass cutting which are then extended to multipass cutting where considerations are given to the change of the actual standoff distance after each pass and the variation of kerf width. These predictive models has been numerically studied for their plausibility by assessing their predicted trends with respect to the various process variables, and verified qualitatively and quantitatively based on the experimental data. The model assessment reveals that the developed models correlate very well with the experimental results and can give adequate predictions of this cutting performance measure in process planning.
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Xu, Shunli. "Modelling the cutting process and cutting performance in abrasive waterjet machining with controlled nozzle oscillation." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16237/.
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Abrasive waterjet (AWJ) cutting is one of the most recently developed manufacturing technologies. It is superior to many other cutting techniques in processing various materials, particularly in processing difficult-to-cut materials. This technology is being increasingly used in various industries. However, its cutting capability in terms of the depth of jet penetration and kerf quality is the major obstruction limiting its further applications. More work is required to fully understand the cutting process and cutting mechanism, and to optimise cutting performance. This thesis presents a comprehensive study on the controlled nozzle oscillation technique aiming at increasing the cutting performance in AWJ machining. In order to understand the current state and development in AWJ cutting, an extensive literature review is carried out. It has found that the reported studies on controlled nozzle oscillation cutting are primarily about the use of large oscillation angles of 10 degrees or more. Nozzle oscillation in the cutting plane with such large oscillation angles results in theoretical geometrical errors on the component profile in contouring. No published attempt has been found on the study of oscillation cutting under small angles although it is a common application in practice. Particularly, there is no reported research on the integration of nozzle oscillation technique into AWJ multipass cutting, which is expected to significantly enhance the cutting performance. An experimental investigation is first undertaken to study the major cutting performance measures in AWJ single pass cutting of an 87% alumina ceramic with controlled nozzle oscillation at small angles. The trends and characteristics of cutting performance quantities with respect to the process parameters as well as the science behind which nozzle oscillation affects the cutting performance have been analysed. It has been shown that as with oscillation cutting at large angles, oscillation at small angles can have an equally significant impact on the cutting performance. When the optimum cutting parameters are used for both nozzle oscillation and normal cutting, the former can statistically increase the depth of cut by 23% and smooth depth of cut by 30.8%, and reduce kerf surface roughness by 11.7% and kerf taper by 54%. It has also been found that if the cutting parameters are not selected properly, nozzle oscillation can reduce some major cutting performance measures. In order to correctly select the process parameters and to optimise the cutting process, the mathematical models for major cutting performance measures have then been developed. The predictive models for the depth of cut in both normal cutting and oscillation cutting are developed by using a dimensional analysis technique. Mathematical models for other major cutting performance measures are also developed with the aid of empirical approach. These mathematical models are verified both qualitatively and quantitatively based on the experimental data. The assessment reveals that the developed models conform well to the experimental results and can provide an effective means for the optimum selection of process variables in AWJ cutting with nozzle oscillation. A further experimental investigation of AWJ cutting of alumina ceramics is carried out in order to study the application of AWJ oscillation technique in multipass cutting. While high nozzle traverse speed with multipass can achieve overall better cutting performance than low traverse speed with single pass in the same elapsed time, it has been found that the different combination of nozzle traverse speed with the number of passes significantly affects cutting process. Optimum combination of nozzle traverse speed with the number of passes is determined to achieve maximum depth of cut. It has also demonstrated that the multipass cutting with low nozzle traverse speed in the first pass and a comparatively high traverse speed for the following passes is a sensible choice for a small kerf taper requirement. When nozzle oscillation is incorporated into multipass cutting, it can greatly increase the depth of cut and reduce kerf taper. The predictive models for the depth of cut in both multipass normal cutting and multipass oscillation cutting are finally developed. With the help of dimensional analysis, the models of the incremental cutting depth for individual pass are derived based on the developed depth of cut models for single pass cutting. The models of depth of cut for a multipass cutting operation are then established by the sum of the incremental cutting depth from each pass. A numerical analysis has verified the models and demonstrated the adequacy of the models' predictions. The models provide an essential basis for the development of optimization strategies for the effective use of the AWJ cutting technology when the multipass cutting technique is used with controlled nozzle oscillation.
Book chapters on the topic "Controlled nozzle oscillation"
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Wang, Jun, and S. Xu. "Enhancing the AWJ Cutting Performance by Multipass Machining with Controlled Nozzle Oscillation." In Advances in Abrasive Technology VIII, 453–58. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-974-1.453.
Full textConference papers on the topic "Controlled nozzle oscillation"
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Arthurs, David, and Samir Ziada. "The Effect of Fluid-Resonant Coupling in High-Speed Impinging Planar Jet Flows." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97141.
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This study investigates the effect of fluid-resonant coupling, i.e. the coupling between unstable modes of an impinging jet with resonant acoustic modes occurring between the nozzle and the impingement surface, on the self-excited oscillations of high-speed impinging planar jet. In order to investigate this phenomenon, a series of experiments have been performed using a high-speed impinging planar jet with varying nozzle thickness (h) and impingement distance (xo), for a single Mach number in the compressible flow regime. The test results reveal that the jet oscillation is controlled by a fluid-dynamic mechanism for small impingement distances, where the unstable mode of the jet is controlled by the impingement ratio. At larger impingement distances, the response is dominated by a fluid-resonant mechanism, in which the various hydrodynamic modes of the jet couple with different resonant acoustic modes occurring between the nozzle and the impingement surface. Within the fluid-resonant regime the system produces acoustic tones that are excited predominantly as a function of the impingement distance, with the nozzle thickness and impingement ratio having only minor effects on the tone frequency. Flow visualization images show that the same unstable mode is excited for multiple nozzle thicknesses at a constant impingement distance, despite the wide variations in associated impingement ratio.
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Janus, Michael C., George A. Richards, M. Joseph Yip, and Edward H. Robey. "Effects of Ambient Conditions and Fuel Composition on Combustion Stability." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-266.
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Recent regulations on NOx emissions are promoting the use of lean premix (LPM) combustion for industrial gas turbines. LPM combustors avoid locally stoichiometric combustion by premixing fuel and air upstream of the reaction region, thereby eliminating the high temperatures that produce thermal NOx. Unfortunately, this style of combustor is prone to combustion oscillation. Significant pressure fluctuations can occur when variations in heat release periodically couple to acoustic modes in the combustion chamber. These oscillations must be controlled because resulting vibration can shorten the life of engine hardware. Laboratory and engine field testing have shown that instability regimes can vary with environmental conditions. These observations prompted this study of the effects of ambient conditions and fuel composition on combustion stability. Tests are conducted on a subscale combustor burning natural gas, propane, and some hydrogen/hydrocarbon mixtures. A premix, swirl-stabilized fuel nozzle typical of industrial gas turbines is used. Experimental and numerical results describe how stability regions may shift as inlet air temperature, humidity, and fuel composition are altered. Results appear to indicate that shifting instability regimes are primarily caused by changes in reaction rate.
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Pennacchi, P., S. Chatterton, and A. Vania. "Modeling of the Dynamic Response of a Pelton Turbine Hydroelectric Plant." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45907.
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The paper presents a detailed numerical model of the dynamics of a Pelton turbine installed in a hydroelectric plant. The model considers in detail the Pelton turbine with all the electromechanical subsystems, such as the main speed governor, the controller and the servoactuator of the turbine nozzle, and the electric generator. In particular it reproduces the effects of pipe elasticity in the penstock, the water inertia and the water compressibility on the turbine behaviour. The dynamics of the surge tank on low frequency pressure waves is also modeled together with the main governor speed loop and the position controllers of the nozzle needle actuators and of the hydraulic electrovalve. Model validation has been made by means of experimental data acquired during some starting tests after a partial revamping of a hydroelectric unit, which involved also the control system of the hydraulic actuators but not the nozzles. The model is used in order to identify the cause of the oscillations of the electric power mainly ascribed to the backlash of the nozzle needle system.
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Mirat, Clément, Daniel Durox, and Thierry Schuller. "Analysis of the Spray and Transfer Function of Swirling Spray Flames From a Multi-Jet Steam Assisted Liquid Fuel Injector." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25111.
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Characterizations of the response of swirling spray flames to flow rate modulations over the entire frequency range remain scarce. This response is addressed here by determining the transfer function of spray flames stabilized on a multi-jet steam-assisted dodecane injector in a turbulent swirling flow confined by a quartz tube. This type of burner is used in some liquid fueled industrial boilers. In the absence of combustion and air flow, a phase Doppler particle analyzer is used to determine the Sauter mean diameter (SMD) of the fuel spray as a function of the atomizing gas to fuel mass flow rate ratio (GLR) injected in the nozzle. For small values of the GLR, the SMD of the generated spray decreases rapidly as the GLR increases. For GLR values above a certain threshold, the SMD reaches a constant value that is independent of the GLR. Transfer functions are measured in this second regime for swirling air flows characterized by a swirl number S = 0.92 that is determined by laser Doppler anemometry. Transfer functions defined as the normalized ratio of OH* or CH* flame chemiluminescence intensity fluctuations divided by the velocity oscillation level measured by laser Doppler velocimetry at the burner outlet are determined as a function of the forcing frequency for a small perturbation level. The response of sooty and non sooty flames at globally lean conditions are examined. Using a set of steady experiments, it is shown that the OH* signal may safely be used to confidently estimate low frequency heat release rate disturbances for both types of flames, but the CH* signal cannot be used in the sooty flame cases. The measured transfer functions of non-sooty spray flames feature many similarities with the transfer function of perfectly premixed swirling flames indicating that their dynamics is also controlled by interference mechanisms that need to be elucidated.
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Yi, Tongxun, and Domenic A. Santavicca. "Flame Transfer Functions and Their Applications to Combustion Analysis and Control." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-60181.
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Heat release rate responses to inlet fuel modulations, i.e. the flame transfer function (FTF), are measured for a turbulent, liquid-fueled, swirl-stabilized, LDI combustor. Fuel modulations are achieved using a motor-driven rotary fuel valve designed specially for this purpose, which is capable of fuel modulations up to 1 kHz. Small-amplitude fuel modulations, typically below 2.0% of the mean fuel, are applied in this study. There is almost no change in FTFs at different fuel modulation amplitude, implying that the derived FTFs are linear and that the induced heat release rate oscillations mainly respond to variations in the instantaneous fuel flow rate rather than in the droplet size and distribution. The gain and phases of the FTFs at different air flow rates and preheat temperature are examined. The instantaneous fuel flow rate is determined from pressure measurements upstream of a fuel nozzle. Applications of the FTF to modeling and control of combustion instability and lean blowout are discussed. Near-LBO stability enhancement using small-amplitude fuel modulation based on the output of a LQG controller is numerically demonstrated.
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Zhou, Jing-Wei, Li-Ping Geng, Yu-Gang Wang, and Fei-Fei Hong. "Experimental and Numerical Study on Flow Field and Heat Transfer Characteristics for a Periodically Unsteady Impinging Jet." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22591.
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An experimental investigation has been carried out to study the effect of unsteady periodically impinging jets on the flow field and heat transfer characteristics. The experiments are performed for steady jets and for typical periodical jets (i.e., sinusoidal and rectangular jets) at frequencies from 1.25 to 40Hz. The periodical jets are produced by a special mass flow rate controller. The investigation shows that the stagnation point heat transfer does not show any enhancement for the periodically impinging jets when the frequency is lower. Various signals of unsteady jets show distinguishing frequency dependences and the rectangular jet, which has a step change in signal function itself, is the most effective one for heat transfer improvement and the degree of enhancement is in the range 30–40% at frequency of 40 Hz. This increase is believed to be caused by higher oscillations and strong entrainments to the ambient fluid. The hotwire anemometry is used to measure the velocity at centerline of the nozzle and PIV is used to measure the phase-locked flow field of the periodically impinging jet. The flow field is also obtained by numerical simulation with CFD.
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Thornton, Jimmy D., Douglas L. Straub, Benjamin T. Chorpening, E. David Huckaby, Geo A. Richards, and Kelly Benson. "A Combustion Control and Diagnostics Sensor for Gas Turbines." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53392.
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The implementation of sophisticated combustion control schemes in modern gas turbines is motivated by the desire to maximize thermodynamic efficiency while meeting NOx emission restrictions. To achieve target NOx levels, modern turbine combustors must operate with a finely controlled fuel-air ratio near the fuel-lean flame extinction limit, where the combustor is most susceptible to instabilities. In turbine configurations with multiple combustors arranged around the annulus, differences in flow splits caused by manufacturing variations or engine wear can compromise engine performance. Optimal combustion control is also complicated by changes in environmental conditions, fuel-quality, or fuel-type. As a consequence, engines must be commissioned in the field with adequate stability margin such that manufacturing tolerances, normally expected component wear, fuel-quality, and environmental conditions will not cause unstable combustion. A lack of robust combustion in-situ monitoring has limited the ability of modern turbines to achieve stable ultra-low emission performance over the entire load range. This paper describes a combustion control and diagnostics sensor (CCADS) that can potentially revolutionize the manner in which modern gas turbines are controlled. This robust sensor uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. The CCADS is integrated into the fuel nozzle such that low cost and long life are achieved. Tests conducted at turbine conditions in laboratory combustors instrumented with CCADS have demonstrated the following potential capabilities: 1) detection of incipient flashback and autoignition 2) detection of incipient lean blowout 3) detection of dynamic pressure oscillations 4) and a qualitative measure of equivalence ratio within the combustor. Many of these capabilities have been reported in other publications with data from an atmospheric combustion rig. This paper will summarize each of the capabilities with recent data at turbine conditions. The expectation is that CCADS will provide the key in-situ monitoring for diagnostics and control of modern gas turbines, allowing them to achieve stable ultra-low emissions performance.
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Chorpening, B. T., E. D. Huckaby, M. L. Morris, J. D. Thornton, and K. J. Benson. "Flame Ionization Distribution and Dynamics Monitoring in a Turbulent Premixed Combustor." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90879.
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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, and progress has been made on detecting and measuring combustion instabilities. In support of this development, a highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the ultraviolet flame 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 ultraviolet (mostly OH*) emission and the corresponding electron and ion distribution near the walls of the combustor. During testing the combustion dynamics were controlled using a fuel feed impedance control technique. This provided flame ionization measurements for both steady and unsteady combustion, without changing the operating parameters of the combustor. Previous testing in this combustor had fewer data acquisition channels, and did not include a full implementation of a CCADS centerbody. This testing included both the guard and sense CCADS electrodes installed on the nozzle centerbody, and an array of 14 wall mounted spark plugs to monitor the flame ionization downstream along the walls of the combustor. This paper reports the results of this testing, focusing on the relationship between the flame ionization, ultraviolet flame emission, and pressure oscillations. Tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with inlet reference velocities of 20 and 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. Data processing included computing the logarithm of the real-time current signal from the guard electrode, to compensate for the exponential decay of the potential field from the electrode. The data show the standard deviation of the guard current to be the most promising statistic investigated for correlation with the standard deviation of the chamber pressure. This correlation could expand the capabilities of CCADS to allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.