The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades a...The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades are prone to undesirable and possibly destructive vibra-tions caused by engine-order excitation or induced by flow itself.To shed more light on this problem and to extend the existing knowledge,this paper presents experimental and numerical study on torsional mode vibration of one blade in a linear blade cascade of flat profiles.In this study,dynamic loading and pressure distributions were investigated at subsonic,supercritical and transonic flow regimes while the blade was kinematically excited by a motor and shaft mechanism at reduced frequencies up to k Z 0.47.Dynamic flow structure development was documented and analyzed based on numerical simulations.Furthermore,dependence of energy transfer over an oscillation cycle on frequency and exit Mach number was investigated.Results revealed significant hysteresis in the flow field configuration particularly at supercrit-ical and transonic cases.Hysteresis is manifested namely by different development of supersonic regions when the oscillating blade passes through the zero deflection during upstroke and downstroke.Resulting aerodynamic moment is non-harmonic and there is an increasing phase lag with respect to the blade deflection when oscillation frequency increases.In majority of investigated regimes,hysteresis resulted in aerodynamic damping of the blade oscillation.展开更多
The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simul...The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simulation of blade flutter in turbomachinery,various incidence angle offsets of the middle blade were modeled.All simulations were run for the flow regime characterized by outlet isentropic Mach number M_(is)=0.5and zero incidence.The results of the LES/RANS simulations(pressure and Mach number distributions)were compared to a baseline RANS model,and to experimental data measured in a high-speed wind tunnel.The numerical results show that both methods overpredict flow separation taking place at the leading edge.In this regard,the hybrid LES/RANS method does not provide superior results compared to the traditional RANS simulations.Nevertheless,the LES/RANS results also capture vortex shedding from the blunt trailing edge.The frequency of the trailing edge vortex shedding in CFD simulations matches perfectly the spectral peak recorded during wind tunnel measurements.展开更多
基金supported by the Ministry of Educa-tion Youth and Sports of the Czech Republic under the grant LUAUS23231 Origins and mechanisms of flutter and non-synchronous vibration in modern turbomachines oper-ating at wide range of regimes.
文摘The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades are prone to undesirable and possibly destructive vibra-tions caused by engine-order excitation or induced by flow itself.To shed more light on this problem and to extend the existing knowledge,this paper presents experimental and numerical study on torsional mode vibration of one blade in a linear blade cascade of flat profiles.In this study,dynamic loading and pressure distributions were investigated at subsonic,supercritical and transonic flow regimes while the blade was kinematically excited by a motor and shaft mechanism at reduced frequencies up to k Z 0.47.Dynamic flow structure development was documented and analyzed based on numerical simulations.Furthermore,dependence of energy transfer over an oscillation cycle on frequency and exit Mach number was investigated.Results revealed significant hysteresis in the flow field configuration particularly at supercrit-ical and transonic cases.Hysteresis is manifested namely by different development of supersonic regions when the oscillating blade passes through the zero deflection during upstroke and downstroke.Resulting aerodynamic moment is non-harmonic and there is an increasing phase lag with respect to the blade deflection when oscillation frequency increases.In majority of investigated regimes,hysteresis resulted in aerodynamic damping of the blade oscillation.
基金supported by the Czech Science Foundation(GACR)(Grant No.20-11537S)Institutional support RVO:61388998。
文摘The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simulation of blade flutter in turbomachinery,various incidence angle offsets of the middle blade were modeled.All simulations were run for the flow regime characterized by outlet isentropic Mach number M_(is)=0.5and zero incidence.The results of the LES/RANS simulations(pressure and Mach number distributions)were compared to a baseline RANS model,and to experimental data measured in a high-speed wind tunnel.The numerical results show that both methods overpredict flow separation taking place at the leading edge.In this regard,the hybrid LES/RANS method does not provide superior results compared to the traditional RANS simulations.Nevertheless,the LES/RANS results also capture vortex shedding from the blunt trailing edge.The frequency of the trailing edge vortex shedding in CFD simulations matches perfectly the spectral peak recorded during wind tunnel measurements.
