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N S Vyas - One of the best experts on this subject based on the ideXlab platform.
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determination of blade stresses under constant speed and transient conditions with nonlinear damping
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 1996Co-Authors: J S Rao, N S VyasAbstract:Determination of resonant stresses is an important step in the life estimation of Turbomachine Blades. Resonance may occur either at a steady operating speed or under transient conditions of operation when the blade passes through a critical speed. Damping plays a significant role in limiting the amplitudes of vibration and stress values. The blade damping mechanism is very complex in nature, because of interfacial slip, material hysteresis, and gas dynamic damping occurring simultaneously. In this paper, a numerical technique to compute the stress response of a turbine blade with nonlinear damping characteristics, during steady and transient operations of the rotor, is presented. Damping is defined as a function of vibratory mode, rotor speed, and strain amplitude. The technique is illustrated by computing the stress levels at resonant rotor speeds for typical operation of a Turbomachine.
Ji Min - One of the best experts on this subject based on the ideXlab platform.
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Fully three-dimensional and viscous semi-inverse method for axial/radial Turbomachine blade design
SURFACE at Syracuse University, 2008Co-Authors: Ji MinAbstract:A fully three-dimensional viscous semi-inverse method for the design of Turbomachine Blades is presented in this work. Built on a time marching Reynolds-Averaged Navier-Stokes solver, the inverse scheme is capable of designing axial/radial Turbomachinery Blades in flow regimes ranging from very low Mach number to transonic/supersonic flows. In order to solve flow at all-speed conditions, the preconditioning technique is incorporated into the basic JST time-marching scheme. The accuracy of the resulting flow solver is verified with documented experimental data and commercial CFD codes. The level of accuracy of the flow solver exhibited in those verification cases is typical of CFD analysis employed in the design process in industry. The inverse method described in the present work takes pressure loading and blade thickness as prescribed quantities and computes the corresponding three-dimensional blade camber surface. In order to have the option of imposing geometrical constraints on the designed blade shapes, a new inverse algorithm is developed to solve the camber surface at specified spanwise pseudo stream-tubes (i.e. along grid lines), while the blade geometry is constructed through ruling (e.g. straight-line element) at the remaining spanwise stations. The new inverse algorithm involves re-formulating the boundary condition on the blade surfaces as a hybrid inverse/analysis boundary condition, preserving the full three-dimensional nature of the flow. The new design procedure can be interpreted as a fully three-dimensional viscous semi-inverse method. The ruled surface design ensures the blade surface smoothness and mechanical integrity as well as achieves cost reduction for the manufacturing process. A numerical target shooting experiment for a mixed flow impeller shows that the semi-inverse method is able to accurately recover the target blade composed of straightline element from a different initial blade. The semi-inverse method is proved to work well with various loading strategies for the mixed flow impeller. It is demonstrated that uniformity of impeller exit flow and performance gain can be achieved with appropriate loading combinations at hub and shroud. An application of this semi-inverse method is also demonstrated through a redesign of an industrial shrouded subsonic centrifugal impeller. The redesigned impeller shows improved performance and operating range from the original one. Preliminary studies of blade designs presented in this work show that through the choice of the prescribed pressure loading profiles, this semi-inverse method can be used to design blade with the following objectives: (1) Various operating envelope. (2) Uniformity of impeller exit flow. (3) Overall performance improvement. By designing blade geometry with the proposed semi-inverse method whereby the blade pressure loading is specified instead of the conventional design approach of manually adjusting the blade angle to achieve blade design objectives, designers can discover blade geometry design space that has not been explored before
Jd Hughes - One of the best experts on this subject based on the ideXlab platform.
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Unsteady aerodynamics in an axial flow compressor
2001Co-Authors: Jd HughesAbstract:Current methods for designing compressor Blades in axial Turbomachines assume that the flow through each blade row is steady. However, interactions associated with the relative motion of neighbouring blade rows are known to produce a disturbance field with both random and periodic components. Despite a growing amount of research into the influence of these disturbances on the downstream row in a rotor-stator or stator-rotor blade row pair, these effects are still not generally accounted for at the design stage. Recent advances in Low Pressure Turbine blade design have shown that incorporating unsteady effects can lead to increases in blade loading beyond the loading limits inferred from steady flow calculations. The current experimental work investigates the unsteady flow behaviour in the neighbourhood of the outlet stator in a 1.5 stage axial flow compressor using thermal anemometry. The aim is to provide a base for more accurate unsteady modelling, and facilitate the development of compressor blade designs which gain maximum benefit from unsteady effects. High-speed data acquisition with synchronised sampling was used to acquire data ensembles for a specific set of rotor wakes, and estimate the periodic and random components of the stator inflow disturbance field. The stator inflow disturbance flow field was altered by clocking of the inlet guide vane row relative to the stator row, and by changing the rotor-stator axial blade row spacing. The interaction of inlet guide vane and rotor wakes was examined using hot-wire measurements downstream of the rotor row. The interaction process was shown to restrict the relative motion of rotor wake fluid and produce local accumulations of low energy fluid on the suction side of the inlet guide vane wakes. Significant circumferential variations in both time-mean velocity and the periodic disturbance component were observed. Clocking of the downstream stator row relative to the inlet guide vanes altered the mid-span stator blade boundary layer behaviour. Hot-wire measurements performed downstream of the stator were used to evaluate the influence of blade row clocking on the stator mid-span viscous losses. The magnitude of periodic fluctuations in ensemble-average stator wake thickness was significantly influenced by IGV wake-rotor wake interaction effects. The changes in time-mean stator losses were marginal. The periodically unsteady laminar to turbulent transition of the stator blade boundary layer was examined using a hot-film surface array mounted on both the suction and pressure surfaces. Observations were made for stator blade loading or incidence cases near stall, design and maximum flow, and for a range of relative axial and circumferential blade row positions. Ensemble average plots of turbulent intermittency and relaxation factor (extent of calmed flow following the passage of a turbulent spot) are presented for a range of inflow disturbance cases. These show the strength of periodic wake-induced transition phenomena to be significantly influenced by incidence, clocking and blade row spacing effects. The periodic, wake-induced, transition in separation bubbles was also altered by changes in blade row spacing. Significant differences between suction and pressure surface transition behaviour were observed, particularly with regard to the strength and extent of calming. Subsequent collaborative work (not reported within) evaluated the quasi-steady application of conventional transition correlation to predict unsteady transition onset on the blading of an embedded axial compressor stage. The viscous/inviscid interaction code MISES was used to calculate the blade surface pressure distributions and boundary layer development. Predictions of the temporal variation in transition onset based on the measured temporal variation of inflow turbulence were compared with the transition onset observations from the compressor stator. Computations for both natural and bypass transition modes indicated that the natural transition mode predicted by a modified e\(^n\) method tended to dominate on the compressor Blades. The success of the MISES transition onset predictions provided strong circumstantial evidence for the importance of natural transition mechanisms in strongly decelerating flow and provided the impetus further experimental investigation. Transitional flow data from the surface film gauges were also analysed using wavelet techniques. The primary use of the wavelet analysis was to facilitate identification of transient instability phenomena in the complex periodic transitional flows present in the stator blade boundary layer. Wavelet analysis and high-pass filtering techniques revealed significant wave packet activity in the unstable laminar flow regions. An algorithm was developed to identify instability waves within the Tollmien-Schlichting (T-S) frequency range. This was combined with a turbulent intermittency detection routine to produce space~time diagrams showing the probability of instability wave occurrence prior to regions of turbulent flow. The implications for transition prediction in decelerating flow regions on axial Turbomachine Blades are discussed
Universitaet Der Bundeswehr Muenchen, Neubiberg Fakultaet Fuer Luft-und Raumfahrttechnik - One of the best experts on this subject based on the ideXlab platform.
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AG TURBO, TURBOTECH II: Vorhaben 1.134 - Optimierung des Stroemungsverhaltens von Verdichtergittern mit CDA-Profilierung. Der Einfluss periodisch instationaerer Zustroemung auf das Transitionsverhalten von Verdichtergittern Abschlussbericht
2000Co-Authors: Teusch R., Fottner L., Kampitsch M., Universitaet Der Bundeswehr Muenchen, Neubiberg Fakultaet Fuer Luft-und RaumfahrttechnikAbstract:For the aerodynamic design of Turbomachine Blades current methods generally apply steady flow theory and consider unsteady effects like blade row interaction, shock-boundary layer interaction, potential effects and secondary flow effects only by means of empirical or semi-empirical correlations. In the context of a modern, cost-oriented blade design efforts are made to increase the aerodynamic blade loading by considering these unsteady effects whereby efficiency and performance are kept constant. This results in a blade count reduction and consequently a weight reduction, but entails a highly three-dimensional and unsteady flow field, which makes great demands on numerical design codes. The primary goals of this work was to investigate the unsteady flow behavior in compressor cascades with controlled diffusion blading under the influence of upstream wakes and to obtain a detailed insight into the physics of unsteady boundary layer behavior. With the obtained data base a validation of unsteady codes should be conducted. The investigated cascades V110 and V111 are representative for the mid section of stator Blades in a high pressure compressor. At the investigated low Reynolds number a loss reduction up to 20% was observed, while at the high Reynolds number a loss increase up to 30% compared to the steady flow case was noted. The numerical results obtained by the unsteady Reynolds-averaged Navier-Stokes code TRACEU which includes a transition correlation showed a very good agreement with the experimental results. Further on indications for new design criteria considering unsteady flow effects were provided. (orig.)Bei der aerodynamischen Auslegung von Turbomaschinenbeschaufelungen beruecksichtigten bisherige Verfahren instationaere Stroemungseffekte wie Schaufelreihen-Interaktion, Stoss-Grenzschicht-Wechselwirkung, Einfluss des Potentialfeldes und Sekundaerstroemungseffekte nur partiell ueber empirische und halbempirische Korrelationen. Im Rahmen einer modernen kostenorientierten Schaufelauslegung wird versucht, durch Optimierung der Schaufelprofile unter Beruecksichtigung der obengenannten instationaeren Effekte bei gleichbleibendem Wirkungsgrad und Leistungsverhalten die aerodynamische Schaufelbelastung zu erhoehen, wodurch eine Reduzierung der Schaufelzahl und damit eine kompaktere Bauweise mit geringerem Gewicht ermoeglicht wird. Das Resultat einer diese Effekte beruecksichtigenden Optimierung ist ein aeusserst komplexes, hochgradig dreidimensionales und instationaeres Stroemungsfeld, das hohe Anforderungen an die numerischen Auslegungsverfahren stellt. Primaeres Ziel dieser Arbeit war, durch eine detaillierte Untersuchung des instationaeren Stroemungsverhaltens um Verdichterschaufeln mit CDA-Profilierung unter dem Einfluss von Nachlaufdellen stromaufliegender Schaufelreihen einen tieferen Einblick in die physikalischen Vorgaenge innerhalb der Schaufelgrenzschicht zu ermoeglichen und mit Hilfe der experimentellen Daten instationaere numerische Verfahren zu validieren. Fuer die beiden untersuchten Verdichtergitter V110 und V111 wurde bei niedriger Zustroem-Reynoldszahl eine bis zu 20%-ige Verlustreduzierung und bei hoher Reynoldszahl ein bis zu 30%-iger Verlustanstieg gegenueber dem stationaeren Fall verzeichnet. Die Nachrechnung der experimentellen Ergebnisse mit dem instationaeren Reynolds-gemittelten Navier-Stokes-Verfahren TRACEU mit Transitionsmodellierung lieferte sehr gute Ergebnisse. Desweiteren wurden Hinweise fuer eine zukuenftige, die instationaeren Effekte beruecksichtigende Schaufelauslegung erteilt. (orig.)SIGLEAvailable from TIB Hannover: RR 6618(2000,6)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman
Jiang Jun - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional inverse method for Turbomachine Blades by the circulation method: The thickness problem
SURFACE at Syracuse University, 1998Co-Authors: Jiang JunAbstract:This dissertation summarizes a procedure to design Blades with finite thickness in three dimensions. In this inverse method, the prescribed quantities are the blade pressure loading shape, the inlet and outlet spanwise distributions of swirl, and the blade thickness distributions, and the primary calculated quantity is the blade geometry. The method is formulated in the fully inverse mode for design of three-dimensional Blades in rotational and compressible flows whereby the blade shape is determined iteratively using the flow tangency condition along the blade surfaces. This technique is demonstrated here in the first instance for the design of two-dimensional cascaded and three-dimensional Blades with finite thickness in inviscid and incompressible flows. In addition, the incoming flow is assumed irrotational so that the only vorticity present in the flowfield is the blade bound and shed vorticities. Design calculations presented for two-dimensional cascaded Blades include an inlet guide vane, an impulse turbine blade, and a compressor blade. Consistency check is carried out for these cascaded blade design calculations using a panel analysis method and the analytical solution for the Gostelow profile. Free-vortex design results are also shown for fully three-dimensional Blades with finite thickness such as an inlet guide vane, a rotor of axial-flow pumps, and a high-flow-coefficient pump inducer with design parameters typically found in industrial applications. These three-dimensional inverse design results are verified using Adamczyk\u27s inviscid code
