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Simple model for investigation of aerodynamic coupling in linear blade cascades
Chládek, Štěpán ; Pešek, Luděk ; Procházka, Pavel P.
Simple viscous-elastic model has been proposed for investigation of aerodynamic coupling in linear blade cascades. One blade is connected with both adjacent blades using idealized springs and dampers which represent viscous fluid. All blades may oscillate with one degree of freedom represented by vertical translation. Energy method using travelling waves model was utilized for aerodynamic damping coefficient derivation. The proposed model does not compute the damping values quantitatively, nevertheless it provides the damping shape analysis. Interesting results are presented within zero and low subsonic flow velocities, where the experiment included velocity flow field measurement.
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Design of low-subsonic blade cascade model for aero-structural dynamic testing
Pešek, Luděk ; Hála, Jindřich ; Šulc, Petr ; Chládek, Štěpán ; Bula, Vítězslav ; Uruba, Václav ; Cibulka, Jan
Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The numerical calculations of two proposed cascades were performed for analysis of influence of stagger angle, incident angle of flow and inter-blade phase angles of the relative movement of blades. The results of numerical simulations of fluid dynamics of non-stationary flow both as viscid and non-viscid are presented. Futhermore the solution of the physical model of the designed cascade including excitation of profiles, measuring of the profile displacement and aerodynamic forces are described.
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Computation of aerodynamic damping in aeroelastic system based on analytical and numerical approach
Chládek, Štěpán ; Horáček, Jaromír ; Zolotarev, Igor
The paper describes computation of aerodynamic damping and natural frequencies of aeroelastic systems. The damping is a critical parameter for the stability analysis of aeroelastic systems. Structural damping of the system is important for very low fluid flow velocities, however by increasing the flow velocity, the aerodynamic damping dominates in the instability search. The damping can be evaluated in time or in frequency domain. The presented computation of aerodynamic damping consists of two analytical and one numerical approach. The analytical approaches are represented by the well-known pk method and the unsteady panel method. The pk method is based on Theodorsen unsteady aerodynamics and on the computation of complex eigenvalues of the system as functions of the flow velocity. The unsteady panel method enables the computation of the interaction between aeroelastic system and fluid flow. The aerodynamic damping is evaluated in time domain from the system response to given initial conditions. The numerical approach is based on the finite volume method (FVM) modelling the complete fluid-structure interaction (FSI) coupled problem. The aerodynamic damping is also computed from the system response to a given initial condition. The results of the mentioned methods are compared for the profile NACA 0012 with two degrees of freedom (2-DOF) for plunge and pitch motion around an elastic axis.
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Evaluation of aerodynamic damping and natural frequencies from numerical simulations and experiments
Chládek, Štěpán ; Horáček, Jaromír ; Zolotarev, Igor
The paper describes different ways for aerodynamic damping and natural frequencies evaluation in a problem of fluid-structure interaction. It is useful for both numerical simulations and experimental measurements. The Fourier transform is used for the frequency evaluation and the damping is evaluated both in time and frequency domain. Significant influence of the chosen sampling frequency and the length of time record on the accuracy of the results are demonstrated both in the numerical simulation and in the experiment that was performed with the flexibly supported profile NACA 0012 with two degrees of freedom.
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Static, spectral and modal analysis of the support of NACA0015 profile
Chládek, Štěpán ; Kozánek, Jan ; Vlček, Václav ; Zolotarev, Igor
In this paper the static and dynamic properties of the new proposed aerodynamical NACA0015 profile were experimentally investigated. The static stiffness of the angular and longitudinal profile support were determined by optical method. By pulse excitation were measured dynamical characteristics for different stiffness and mass configurations and identified corresponding spectral and modal properties. It will be useful for appropriate tuning of this dynamical system to achieve the flutter vibration in aerodynamical tunnel.
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Identification of the aeroelastic profile based on optical measurement
Chládek, Štěpán ; Zolotarev, Igor
Abstract: This paper introduces an identification of an aeroelastic profile as n – degrees of freedom linear system. The common identification is based on the excitation of the system with an impact hammer and the measurement of the response by an acceleration sensor and using the transfer functions the modal properties are evaluated. This approach gives a disadvantage in the sense of influence of the system structural properties. In this paper the identification of the dynamical system is based on the optical measurement of the system response. The great advantages of this approach are both the low influence of the measuring devices to the system properties and the high precision of the measurement. The theory has been verified on the aeroelastic profile NACA 0012 with 2 degrees of freedom and the results are presented.
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Analytical and numerical approach to the airfoil stability computation
Chládek, Štěpán ; Horáček, Jaromír
The fluid structure interaction (FSI) represents an important task in many applications. This paper deals with interaction of airfoil and fluid flow and compares two possible ways of computation of the stability boundaries of the system. The airfoil has two degrees of freedom represented by translation h(t) and rotation a(t). The flow acts on the airfoil with aerodynamic forces depending on the flow velocity. Two methods for calculation of the critical flow velocity, when the airfoil loses aeroleastic stability, are described.
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Aeroelastic experiments with the structural properties variation
Chládek, Štěpán ; Zolotarev, Igor ; Uruba, Václav
The paper measurements on a model of the airfoil NACA0012. Usually there is a limit range of the flow velocity in the wind tunnel. The chosen wind tunnel is usually fixed, the only one possibility is to modify the structural properties of the experimental stand. There are presented two kinds of modifications, one is based on the geometry variation, the other one on the added mass approach. Both of them have been verified experimentally.
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