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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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Measurement of fluttering airfoil with two degrees of freedom
Štěpán, M. ; Šidlof, P. ; Vlček, Václav
The paper focuses on measurement of vibrating motion of an aerodynamic profile in wind tunnel of the Institute of Thermomechanics. The physical model of the NACA 0015 airfoil has been designed and fabricated, allowing motion with two degrees of freedom: vertical motion and rotation around the elastic axis. The motion of the airfoil was registered by length optical incremental gauge, separately by the high speed camera with synchronous measurement of pressures on the surface of airfoil. The amplified signals from the pressure sensors and strain gauges were acquired using the National Instruments data cards and Dewesoft measuring software. The results of the measurement are presented too.
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Unsteady aerodynamic forces measured on a fluttering profil
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan
The evaluations of optical measurements of the flow field near the fluttering profile NACA0015 with two-degrees of freedom are presented. Mach number of the airflow was M = 0.21 and M = 0.45, the boundaries of the flutter occurrence. Aerodynamic forces acting on the profile were evaluated in the drag and lift components which enabled to obtain independently the forces corresponding to the upper and lower surfaces of the profile. Using the mentioned decomposition, the new information about mechanism of flutter properties was obtained. The force effects on the upper and lower surfaces are in opposite phases and they are partially eliminated as a result of the circulation around the profile. The cycle changes of this forces cause the permanent energy contribution from the airflow to the vibrating system.
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Vibration evaluation and identification in mechanical engineering
Kozánek, Jan
This paper deals with parametric identification in mechanical engineering domain. We assume a linear mathematical model of vibrating machine in discrete form and in frequency domain, defined by stiffness, viscous damping and mass matrices and by the corresponding resolvent. Parametric identification is understood as the evaluation of the measured data from dynamic experiments and its methods can be divided into "indirect" (obtaining spectral and modal properties - modal analysis methods) and "direct" (determination of the coefficient matrices of the mathematical model). We mention also the parametric identification methods for parametric and evolutive dynamic systems , the loss of asymptotic stability and dynamic systems with weak nonlinearities.
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