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Numerical and Experimental Investigation of the Flow Field in Five Blade Linear Cascade in Subsonic Flow
Šnábl, Pavel ; Chindada, Sony ; Bublík, O. ; Procházka, Pavel P. ; Prasad, Chandra Shekhar
In large steam turbines, last stage blades are very long and must be designed very thin and with no shroud to minimize the centrifugal force which leads to low eigenfrequencies and low structural damping. In this case, aero-elastic damping plays important role on last stage bladed disc’s dynamics. Three major aero-elastic issues found in turbomachinery are forced response, non-synchronous vibrations, and flutter. Flutter is an unstable, self-excited vibration resulting from coupling between the structural vibrations and unsteady aerodynamic forces. It is clear that this unstable behaviour must be avoided and predictions of flutter behaviour need to be performed during design stage of the turbine.\n
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The effect of the pitch support elasticity on the NACA0015 profile aeroelastic properties
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan
The aeroelastic experiments realized in wind tunnel of the Institute of Thermomechanics with Mach numbers M ~ 0.20-0.22 and with the interval of Reynolds numbers Re = (2.4-2.6).105, are presented. These results correspond to the self-excited vibration of the profile NACA0015 with two degrees of freedom allowing the profile rotation in 1/3-chord axis and allowing the vertical displacement of the profile. The dependence of vibration frequency on the wind-flow velocity has been obtained. Comparing with the previous experiments the influence of the pitch support elasticity on the profile aeroelastic properties was determined.
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Some atypical flutter characteristics of the NACA0015 profile
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan ; Štěpán, M.
The part of the aeroelastic experiments with profile carried out in wind tunnel of the Institute of Thermomechanics, v.v.i. at stream velocity M = 0.15-0.38 in the interval of Reynolds numbers Re = (1.8-5.0)•105 is presented. The results relate to the self-excited vibration of the profile NACA0015, which had two degrees of freedom allowing rotation and transverse displacement of the profile. The elasticity of the two degrees of freedom support has not been, during the experiments, changed. The dependence of Strouhal numbers on the speed of the stream.has been obtained. In one case the excitation of an unstable state occured and during the measurement the jump to a stable state arised. The kinematics of the model during this transition is described.in detail.
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Some NACA0015 profile support variants with self-excited vibration in subsonic fluid flow
Vlček, Václav ; Štěpán, M. ; Zolotarev, Igor ; Kozánek, Jan
One of the important domain of the contemporary aeroelasticity is the self-excited vibration of isolated profiles together with the self-excited vibration of profiles located in blade cascades. The Institute of Thermomechanics of the AS is engaged in group of projects concerning this aeroelastic problem. Results presented here were obtained solving a part of them [1-5].This experiments were realized in the wind tunnel of suction type placed in the laboratory of the Institute in Nový Knín. Profile NACA0015 with two degrees of freedom support was used. Profile was embedded with variable rotational and translational elasticity. The attention of this paper is concentrated on the time records and corresponding spectra of the translational and rotational movement during the self-excited vibration of the profile. Further results related to other parameters of this vibration will be published separately.
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Symetric profile experiments with a velocity near the stall-flutter cut-off
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan
Aeroelastic experiments with the profile NACA0015 with two degrees of freedom were realized in aerodynamic tunnel of the Institute of Thermomechanics, Czech Academy of Sciences, Prague. Attention was concentrated to the profile behaviour at velocity where the profile is just on the end of the velocity interval, where stall-flutter occurs. The flow field was measured with Mach-Zehnder interferometer, interferograms were registered with the high speed camera. Difference in the profile behaviour in these conditions was registered.
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Flutter at a low velocity
Vlček, Václav ; Kozánek, Jan ; Zolotarev, Igor
Aeroelastic experiments with the profile NACA0015 were realized in the suction type aerodynamic tunnel of the Institute of Thermomechanics, Czech Academy of Sciences, Prague. The profile had two degrees of freedom realized in translation and rotation motion and flow velocity was just up its critical value. The flow field was measured with interferometry method and the results obtained at the velocity M = 0.23 in the flutter regime are presented. The evaluation of interferogramms enabled to determine the components of the drag and lift forces.
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