Aerodynamic Excitation Force Research Articles

Evolution of turbine flow field and aerodynamic excitation force under rotating detonation environment

Evolution of turbine flow field and aerodynamic excitation force under rotating detonation environment

Combination resonance and primary resonance characteristics of a dual-rotor system under the condition of the synchronous impact of the inter-shaft bearing

The internal structure of many aero-engines is designed with a dual-rotor system. Up to now, there have been few studies on the influence of aerodynamic excitation on the dual-rotor system. The phenomenon of synchronous impact may occur when the frequency of the aerodynamic excitation force of the fan blade is close to the characteristic frequency of the inter-shaft bearing. This paper investigates the dynamic characteristics of a dual-rotor system under the condition of synchronous impact. The system's motion equations are formulated considering the complex nonlinearities of the inter-shaft bearing, such as Hertz contact force of 10/9 exponential function, clearance, and periodic varying compliance. In addition, the inter-shaft bearing with a local defect is considered. The fan blade’s aerodynamic excitation force is modeled by synthesizing multiple harmonic excitation forces, the amplitudes of which are obtained by the Fourier series expansion. Numerical simulations are employed to get the dynamic responses of the system. The results show that the dynamic characteristic of the dual-rotor system at the primary resonance caused by the high-pressure (H.P.) rotor is not changed by the aerodynamic excitation force, while the primary resonance caused by the low-pressure (L.P.) rotor increases significantly. However, three aerodynamic resonances of the amplitude-frequency response of the dual-rotor system are emerging in the low-frequency region (124, 146 and 186 rad/s). When the synchronous impact phenomenon occurs, the amplitude of the three resonance peaks will increase twice compared to the original status, leading to a doubled increase in the dynamic load of the inter-shaft bearing. The characteristics of the dual-rotor system affected by the parameters such as initial phase difference of local defect, rotor eccentricity of system, clearance of inter-shaft bearing, and the stiffness and damping of supports are discussed in detail. The results obtained provide a deep insight into the mechanism of synchronous impact.

Simulation and experimental investigation on vibration of a radial turbine wheel using a two-way FSI approach

When turbine blades of a radial turbocharger are subjected to an unsteady aerodynamic load excitation force, high cycle fatigue of the turbine blades will occur when the excitation force reaches a certain level. The fatigue of the radial turbine wheel is affected by both static and dynamic stresses, and high cycle fatigue occurs when the dynamic stress reaches a certain amplitude. In this study, a two-way fluid–structure interaction (FSI) analysis method was used to predict the dynamic excitation force and dynamic response of the turbine wheel, which can precisely predict the forced vibration of the turbine wheel under the condition of rotor–stator interaction. A resonance intersection point was excited by the stator (turbine housing vortex tongue) of the radial turbocharger as the operating boundary condition, and the aerodynamic excitation caused by the rotor–stator interaction and the vibration amplitude of the turbine blade was predicted and analysed. A turbine blade dynamic measurement system (tip timing) was used to measure the dynamic deformation of turbine blades for turbochargers in real time. The simulation and measurement results showed that the errors of the predicted vibration displacements and measured mistuning blades were within the acceptable range, and the two-way FSI analysis method can precisely predict the forced vibration of the model.

Effects of a Single Blade Incidence Angle Offset on Adjacent Blades in a Linear Cascade

The paper presents a numerical and experimental investigation of the effect of incindence angle offset in a two-dimensional section of a flat blade cascade in a high-speed wind tunnel. The aim of the current work is tp determine the aerodynamic excitation forces and approximation of the unsteady blade-loading function using a quasi-stationary approach. The numerical simulations were performed with an in-house finite-volume code built on the top of the OpenFOAM framework. The experimental data were acquired for regimes corresponding to the numerical setup. The comparison of the computational and experimental results is shown for the static pressure distributions on three blades and upstream and downstream of the cascade. The plot of the aerodynamic moments acting on all five blades shows that the adjacent blades are significantly influenced by the angular offset of the middle blade.

Rub-Impact Dynamics of Shrouded Blades under Bending-Torsion Coupling Vibration

Shroud devices which are typical cyclic symmetric structures are widely used to reduce the vibration of turbine blades in aero engines. Asymmetric rub-impact of adjacent shrouds or aerodynamic excitation forces can excite the bending-torsion coupling vibration of shrouded blades, which will lead to complex contact motions. The aim of this paper is to study the rub-impact dynamic characteristics of bending-torsion coupling vibration of shrouded blades using a numerical method. The contact-separation transition mechanism under complex motions is studied, the corresponding boundary conditions are set up, and the influence of moments of contact forces and aerodynamic excitation forces on the motion of the blade is considered. A three-degree-of-freedom mass-spring model including two mass blocks with the same size and shape is established to simulate the bending-torsion coupling vibration, and the dynamic equations of shrouded blades under different contact conditions are derived. An algorithm based on the fourth-order Runge–Kutta method is presented for simulations. Variation laws of the forced response characteristics of shrouded blades under different parameters are studied, on the basis of which the method to evaluate the vibration reduction characteristics of the shrouded blade system when the motion of the blade is chaotic is discussed. Then, the vibration reduction law of shrouded blades under bending-torsion coupling vibration is obtained.

Aerodynamic Excitation Forces Generated by Rotating Propeller Fan

Aerodynamic Excitation Forces Generated by Rotating Propeller Fan

Numerical analysis of the aerodynamic performance and excitation forces in a transonic turbine cascade with flat-tip and squealer-tip blades

The purpose of this paper is to numerically investigate the effect of blade tip clearance and its structure on the turbine aerodynamic performance and excitation force on blades in a transonic turbine cascade. Hence, circular cascades with flat-tip and squealer-tip blades and eight different tip clearances based on the SNECMA transonic turbine were established and the rotational effect was taking into consideration. The simulations were performed by solving the RANS equations and the SST turbulence model was used. The results show that tip clearance and tip structure have a significant influence on the turbine efficiency and excitation forces. Smaller tip clearance and squealer tip structure can reduce the tip leakage flow and leads to higher turbine efficiency. The tangential blade force varies nonlinearly with tip clearance since the leakage flow significantly changes the static pressure distributions on blade surfaces. Further, the excitation force factor was also calculated and illustrated.

Dynamic Analysis of Flexible Shaft and Elastic Disk Rotor System Based on the Effect of Alford Force

Taken the flexible shaft and elastic disk rotor system as the research object, vibration differential equations are established by the modal synthesis method. Based on the Runge–Kutta method of direct integration, dynamic equations are solved successfully. Then, the effects of Alford force caused by the airflow excitation are researched on the stability and dynamic response. The results show modal vibration of the disk takes a great effect on the coupled natural frequency of shaft transverse vibration in the high rotational speed region. The effect of shaft‐disk coupling makes rotor frequency to decrease, and different rotational speeds have little effect on rotor frequency. Eccentric distance is sensitive to the amplitude of rotor response, but it has little effect on rotor stability, motion law, and relative relationship of two response frequencies. The proportion of rotor responses caused by aerodynamic excitation force becomes larger with the increase of rotational speed and disk radius. However, the proportion decreases with the second support moving to the right, and it is helpful for the stable operation of the rotor system.

Numerical Investigation on Aeroelastic Behavior of Composite Material Plate Excited by Pulsed Air Jet

Nowadays, carbon fiber composite material is becoming more and more popular in aero engine industry due to its high specific strength and stiffness. Laminate carbon fiber composite material is widely used to manufacture the high load wide chord fan blade, containment casing, etc. The aeroelastic behavior of composite product is critical for the optimization of the product design and manufacturing. In order to explore its aeroelastic property, this paper discusses the coupled simulation of aerodynamic excitation applied on laminate composite material plate. Mechanical behavior of composite material plate is different from that of isotropic material plate such as metal plate, because it is anisotropy and has relative high mechanical damping due to resin between plies. These plates to be studied are designed using 4 different layup configurations which follow the design methods for composite fan blade. The numerical simulation of force response analysis mainly uses single frequency mechanical force input to simulate the electromagnetic shakers or other actuators, which could transmit mechanical force to the test parts. Meanwhile, pulsed air excitation is another way to “shake” the test parts. This excitation method induces aero damping into the test part and simulates the unsteady flow in aero engine, which could cause aeroelastic problems, such as flutter, forced response and non-synchronous vibration (NSV). In this study, numerical simulation using coupled method is conducted to explore the characteristics of laminate composite plates and the property of aerodynamic excitation force generated by pulsed air jet device. Modal analysis of composite plate shows that different ply stacking sequences have a significant impact on the plate vibration characteristics. Air pulse frequency and amplitude in flow field analysis are calibrated by hot wire anemometer results. As the air pulse frequency and amplitude are varied, incident angle of flow and layup configurations of plate can be analyzed in details by the simulations. Through the comparisons of all these factors, air pulse excitation property and the aeroelastic behavior of composite material plate are estimated. It would provide a possible way to guide the next-step experimental work with the pulsed air rig. The new composite fan blade design can be evaluated through the process.

S1610101 ファンによる流体加振力とモータ足側反力 : モータ足側反力の計算式の作成([S161]家庭電化機器/業務用電化機器)

S1610101 ファンによる流体加振力とモータ足側反力 : モータ足側反力の計算式の作成([S161]家庭電化機器/業務用電化機器)

J-1-2 ファンによる流体加振力の計算とモータ足側反力の検討

J-1-2 ファンによる流体加振力の計算とモータ足側反力の検討

A Study on Unsteady Aerodynamic Excitation Forces on Radial Turbine Blade due to Rotor-Stator Interaction

A Study on Unsteady Aerodynamic Excitation Forces on Radial Turbine Blade due to Rotor-Stator Interaction

Blade Excitation in Pulse-Charged Mixed-Flow Turbocharger Turbines

In this article, a fully three-dimensional computational modeling approach in the time and frequency domain is presented, which allows to accurately predicting fluid-structure interactions in pulse-charged mixed-flow turbocharger turbines. As part of the approach, a transient computational fluid mechanics analysis is performed based on the compressible inviscid Euler equations covering an entire engine cycle. The resulting harmonic orders of aerodynamic excitation are imposed in a forced response analysis of the respective eigenvector to determine effective stress amplitudes. The modeling approach is validated with experimental results based on various mixed-flow turbine designs. It is shown that the numerical results accurately predict the measured stress levels. The numerical approach can be used in the turbine design and optimization process. Aerodynamic excitation forces are the main reason for high cycle fatigue in turbocharger turbines and therefore a fundamental understanding is of key importance.

Vibration Suppression of a Helicopter Using Pendulum Absorbers : First Elastic Mode of a Blade

Centrifugal pendulum vibration absorbers are widely used as a vibration suppression device for helicopters. The vibration characteristics of this absorber have been investigated by utilizing linear anti-resonance theory. However, it has been noted that nonlinear characteristics appear when pendulums swing at large amplitudes. The authors investigated vibration suppression characteristics of pendulum absorbers considering nonlinear characteristics of pendulums. In the first report, we investigated a two-degree-of-freedom (2DOF) system composed of a rigid blade and a pendulum. In this system, the blade was excited by a harmonic deflection motion of the shaft. In the second report, we investigated a three-degree-of-freedom system composed of a fuselage, a rigid blade and a pendulum. In this third study, the model has 3DOF and is composed of a blade, a pendulum and a rotor mount. The blade is assumed to be flexible and only the first elastic mode is considered. An aerodynamic excitation force is applied to the blade. The vibration suppression characteristics of this system are investigated theoretically and experimentally.

振子式動吸振器によるヘリコプタの制振 : ブレードの弾性1次モード(D&D2009)

Centrifugal pendulum vibration absorbers are widely used as the vibration suppression devise for helicopters. The vibration characteristics of this absorber has been investigated by applying the linear theory on anti-resonance. However, the nonlinear characteristics appear when the pendulum swings with large amplitude. The authors studied vibration suppression characteristics of pendulum absorbers considering nonlinear characteristics of pendulums. In the first report, we investigated a two-degree-of-freedom system composed of a rigid rotor blade and a pendulum. In this system, the blade was excited by a harmonic deflection motion of the shaft. In the second report, we investigated a three-degree-of-freedom system composed of a fuselage, a rigid blade and a pendulum. In this paper, the model has three degrees of freedom and is composed of a blade, a pendulum and a rotor mount. The blade is flexible and only the first mode is considered. An aerodynamic excitation force applies to the blade. The vibration suppression characteristics of this system are investigated theoretically and experimentally.

Direct measurement of aerodynamic excitation force generated by rotating-blade fan

A method for measuring the aerodynamic excitation force of a rotating-blade fan has been developed. Calculating the vibration response of the structure is a useful solution for reducing the cost and weight of the air conditioner, which consists of a structure enclosed by thin metal plates. To calculate the vibration response of a thin plate excited by the aerodynamic force of the rotating fan, the measured pressure was transformed into the amplitude and phase angle of the aerodynamic force. Only the basic frequency of the blade-passing component, at which the largest fluctuation pressure occurs, was used in this calculation. Using the transformed amplitude and phase of the force, the vibration response of the thin plate structure was accurately calculated.

New Steps to Improve Rotordynamic Stability Predictions of Centrifugal Compressors

Improved rotordynamic stability is desired by end users, and centrifugal compressor manufacturers are expected to meet, if not exceed, this expectation. Compressor manufacturers are required to design and build machines that are rotordynamically stable on the test stand and in the field. Confidence has been established in predicting the excitation forces from seals and bearings, but impeller aerodynamic excitation forces continue to be a challenge. While much attention is paid to impellers from an aerodynamic performance point of view, more efforts are needed from a rotordynamic standpoint. A high-pressure, reinjection centrifugal compressor is analyzed in order to predict rotordynamic stability using the best available resources for seals and bearings. Impeller shroud forces are predicted using the bulk-flow model developed by Gupta and Childs (Gupta, M., and Childs, D., Proc. of ASME Turbo Expo 2000, Power for Land, Sea, and Air). Each impeller stage is analyzed and an attempt is made to improve the estimation of impeller aerodynamic excitation forces. Logarithmic decrement (log dec) predictions for the full rotor model consisting of all the stages and seals are compared to the full-load full-pressure test measured values using a magnetic bearing exciter. A good correlation is obtained between the measured test results and analytical predictions.

An Experimental Study of Reduction for Aerodynamic Excitation to Head-Arm of HDD

This paper deals with reduction methods of aerodynamic excitation for a head-arm of HDD experimentally. Two types of measurement were conducted ; flow visualization around enlarged head-arm models by using a smoke tunnel, and flow field between co-rotating disks of HDD. On the flow visualization, we put a focus on separation of the flow. It is found that width of the separation can be reduced by optimizing design of the hole in the head-arm, chamfering front edge of the head-arm, and so. On the flow field, we examined flow vectors, fluctuation of the flow, frequency characteristics, influence by existence of the head-arm, and so. No factors especially exciting the head-arm were recognized. Therefore, aerodynamic excitation force is considered to be mainly due to the turbulence caused by separation, flow instability of wake, and so.

와류진동 조절에 의한 유동가진 공동 내부의 음압 제어

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the leading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

Experimental Study of Aerodynamic Excitation Mechanism in Shroud Clearance on Flow-induced Disk Vibration of HDD

This paper deals with an excitation mechanism of the flow induced disk vibration of HDD. Since the shroud clearance is very influential factor in the disk vibration, we examined experimentally how the aerodynamic excitation force in the shroud clearance generates. A flow condition in the shroud clearance and the relation between the flow condition and the disk vibration were investigated. Experiments show that making the shroud clearance small leads to reduction of the excitation force and that the excitation force occurs mainly near the disk edge. The vibration amplitude of the disk has a relation with the Reynolds number on the shroud clearance as a characteristic length, so it is considered necessary to make the circumferential flow in the shroud clearance less turbulent for reduction of vibration of the disks.