Aerodynamic Excitation Research Articles

Probability analysis of compressor blade vibration based on radial basis function extremum neural network method

To enhance the transient response and modeling accuracy of compressor blade vibration characteristics in time domain dynamic reliability analysis, a method called the radial basis function extremum neural network (RBFENN) is proposed. This method combines the radial basis function neural network (RBFNN) with the extreme response surface method (ERSM). By considering the time domain and frequency domain characteristics of unsteady aerodynamic excitation on blades affected by multi-row stator/rotor interference, the stress response distribution of the blades is determined through deterministic analysis. The RBFENN mathematical model is established using RBFNN to address the high nonlinearity in surrogate modeling. The ERSM is used to process the transient problem of motion reliability analysis, taking extreme values into account throughout the response process. In evaluating the vibrational reliability of the compressor blades, the maximum stress is considered as the primary focus of the study, taking into account the stochastic nature of aerodynamic excitation frequency, rotational velocity, and material parameters. It is observed that the unsteady aerodynamic excitation induces higher-order harmonic resonances in the blade velocity margin, resulting in increased stress at the leading edge of the blade root. This stress distribution follows a normal distribution pattern. A comparison among Monte Carlo methods, ERSM, and RBFENN demonstrates the superiority of the proposed RBFENN method in terms of computational accuracy and efficiency. This study introduces the RBFENN method as a learning-based approach for blade vibration reliability design, enriching the theory of mechanical reliability.

Rapid dynamic load estimation procedure for lifting propellers in forward flight

AbstractLifting propellers operate at oblique inflow and thus encounter severe dynamic loads during forward flight, impacting structural integrity, fatigue, and vibration. Numerical optimization approaches consider aerodynamic, structural mechanical, and aeroacoustic aspects within preliminary design. To also account for dynamic loads during forward flight, a novel procedure allows their rapid estimation. Based on steady-state simulations combining strip theory and finite beam elements, aerodynamic excitation, damping, and stiffness are defined in the frequency domain. Loads are derived through a linear inflow model and quasi-steady aerodynamics. Damping and stiffness loads are linearized and transferred into matrix form to calculate the frequency response. The computationally expensive need for simulations in the time domain is thus avoided. Applicability extends to both fixed and variable pitch lifting propellers utilized in large multicopters for cargo or passenger transportation. Comparisons to time-marching simulations show good agreement with deviations of approximately 10 %. The analytical derivation yields physical insights to understand and reduce dynamic loads and their magnification due to resonance.

Interior noise characteristics, source identification and its quantification contribution of 400 km/h high-speed train in different operating environments

Noise level is one of the core technical indicators of high-speed trains, especially for a speed of 400 km/h. Noise source identification and its contribution quantification are key for interior noise control. This article takes a certain high-speed train running up to 400 km/h as the research object. Firstly, based on the interior noise spectrum and experimental results of source identification based on spherical harmonic function, the main source locations and energy distribution inside the train are determined. Secondly, through polynomial fitting, the correlation between vibration and noise in various areas inside and outside the train and speed is determined. Subsequently, by calculating the energy contribution through area integration, the noise contribution of each interior region is determined, and then the variation law of the noise contribution of each region with the speed is determined, and the quantitative contributions of various areas inside the train are given when the high-speed train is running at 400 km/h. Finally, the vibration and noise inside the train, aerodynamic noise on the train body surface, and noise in the bogie area in open lines and tunnel operating environments are compared and analyzed, as well as their variation laws with speed. The main noise sources inside the train under two types of operating environments are identified, and the contribution rates of noise sources in different areas inside the train are analyzed, further studying the interior noise and vibration transmission characteristics. The results show that, when the high-speed train is running at 400 km/h in open line operating environment, the significant frequency range of interior noise is 40 Hz ∼ 2000 Hz, and dominant interior noise sources are located in the roof and floor. In the tunnel operating environment, the significant frequency range of interior noise is 160 Hz ∼ 1000 Hz, and the primary sources of interior noise are predominantly located in the left window and floor. For the sidewall area, the interior noise comes mainly from the vibration of the inner sidewall when in open line operating environment, while in tunnel operating environment, the interior noise comes mainly from the aerodynamic excitation of the body surface.

Nonlinear characteristics and radial-bending-torsional vibration of a blade with breathing crack

Rotor failures due to cracked blades are frequently observed in rotating machinery. The identification of cracking state of rotating blade based on vibration characteristics has garnered a lot of attention. However, nonlinear characteristics and vibration combining in radial, bending and torsional directions of a rotating blade induced by the crack breathing is yet not clear. This paper proposes a radial-bending-torsional dynamic model of rotating blade with breathing crack. A time-varying integration method is proposed for determining the crack state based on the strain energy release rate. The crack breathing behavior is described by Boolean operation and the numerical integration are applied to open or close the crack. The model is validated through modal analysis, vibration responses and contact state of crack surface. Frequency veering is changed between the 2nd flap and 1st edgewise frequency due to the existence of crack. Strong nonlinear behaviors are found in the radial and torsional vibrations because of the crack breathing. Nonlinearities are also found in the combined vibrations between the radial-bending and the bending-torsional directions. Radial and torsional vibration amplitude levels can be used as an indication of blade crack failure, but the applicability depends on the absolute response decided by the aerodynamic excitation and resonant vibration. These findings can serve as guidance in crack identification and cracking state monitoring of rotating blades.

Study on the Influence of Volute Throat Jet on Excitation Vibration Alleviation of Radial Turbine Blade

Abstract Turbine blade fracture, resulting from high-cycle fatigue (HCF), is the most commonly observed failure mode of turbochargers. In a vaneless turbine, the radial turbine blade is susceptible to HCF under excessive aerodynamic excitation due to the flow field distortion caused by the volute tongue. The present study explores a technique to mitigate blade excitation by reducing pressure disturbance in the volute tongue area. The gas with higher pressure in the inlet section of the volute is transferred to the low-static pressure area upstream of the volute tongue through a throat jet hole. The usage of high-pressure gas improved the homogeneity of the flow field near the volute tongue. The study investigates the mitigation of high-pressure gas jet on turbine blade excitation, the impact of jet hole geometry on the suppression effect of the blade vibration, and the effect of high-pressure jet on turbine performance using numerical simulation of unsteady flow fields. The results indicate that the jet flow has a substantial impact on dampening the blade vibrations. The harmonic pressure amplitude at the monitor point located within the high blade vibration amplitude region is reduced by up to 56%. Generalized pressure analysis reveals that the aerodynamic excitation of the turbine blades is significantly reduced. Experimental evidence verifies the effectiveness of the jet hole scheme in reducing blade vibration. Moreover, the jet hole has a negligible effect on turbine efficiency. However, there is a degree of increased stress in the volute tongue with a jet hole which needs to be evaluated in engineering applications.

Analysis of human body vibration response on high-speed trains under crosswinds

The increase in the speed of high-speed trains and the widespread use of lightweight vehicle body technology have made vehicle systems more sensitive to aerodynamic excitation. However, few studies have focused on the worsening of passenger ride comfort, as opposed to just safety, when trains pass along windy railway lines. This study first analyzes the connection between flow structure and aerodynamic load, using bidimensional empirical mode decomposition (BEMD). Then, it examines the effect of aerodynamic loads on the vibration characteristics of vehicles and human bodies, at different speeds under crosswinds, by combining a vehicle-track-seat-human body coupling model. Finally, the effects of crosswinds on vehicle and human body vibration are analyzed, including differences in vibration characteristics of the human head when in different positions. The BEMD results indicate that the flow field around the vehicle is dominated by low-frequency oscillation. These low-frequency components show close alignment with the aerodynamic loads’ main frequency, and the high-speed trains’ natural frequency, which may lead to vehicle resonance shaking, and to derailment. Additionally, it is found that lateral vibration comfort for human legs and thighs is worst in both the head and middle cars, while vertical vibration comfort for the human head is worst in the head car. When running at three speeds under crosswinds, fluctuations in aerodynamic loads and track irregularities are major causes of discomfort for humans, particularly affecting vertical vibration comfort. In crosswinds, vertical vibration of the human head is significantly greater than lateral vibration, indicating a loss of comfort, primarily in the vertical direction, when trains are excited by crosswinds. It is observed that lateral vibration comfort is worst at the front end of the head car, but best at their rear end. Vertical vibration comfort is best in the middle section of the head car.

A Study on the Effect of Turbulence Intensity on Dual Vertical-Axis Wind Turbine Aerodynamic Performance

Examining dual vertical-axis wind turbines (VAWTs) across various turbulence scenarios is crucial for advancing the efficiency of urban energy generation and promoting sustainable development. This study introduces a novel approach by employing two-dimensional numerical analysis through computational fluid dynamics (CFD) software to investigate the performance of VAWTs under varying turbulence intensity conditions, a topic that has been relatively unexplored in existing research. The analysis focuses on the self-starting capabilities and the effective utilization of wind energy, which are key factors in urban wind turbine deployment. The results reveal that while the impact of increased turbulence intensity on the self-starting performance of VAWTs is modest, there is a significant improvement in wind energy utilization within a specific turbulence range, leading to an average power increase of 1.41%. This phenomenon is attributed to the more complex flow field induced by heightened turbulence intensity, which delays the onset of dynamic stall through non-uniform aerodynamic excitation of the blade boundary layer. Additionally, the inherent interaction among VAWTs contributes to enhanced turbine output power. However, this study also highlights the trade-off between increased power and the potential for significant fatigue issues in the turbine rotor. These findings provide new insights into the optimal deployment of VAWTs in urban environments, offering practical recommendations for maximizing energy efficiency while mitigating fatigue-related risks.

Effect of tip clearance on non-synchronous propagating flow disturbances of compressor rotors under high aerodynamic loading conditions

The complex tip flow instability and its induced non-synchronous vibration have become significant challenges, especially as aerodynamic loading continues to increase. This study investigates the effects of tip clearance on non-synchronous propagating flow disturbances of compressor rotors under high aerodynamic loading conditions by conducting full-annulus unsteady numerical simulations with three typical tip clearance values for a 1-1/2 stage transonic compressor. The non-synchronous aerodynamic excitation frequency, circumferential mode characteristics, and annular unstable flow structures are analyzed under near stall conditions. The results show that the total pressure ratio and normalized mass flow parameters first increase and then decrease as the tip clearance increases from 0.5%C (where C represents the tip chord length) to 2%C under high aerodynamic loading conditions, instead of constantly decreasing. For the 0.5%C tip clearance case, the traveling large-scale tornado-like separation vortices cause a low non-synchronous aerodynamic excitation frequency and severe pressure fluctuations. The periodic shedding and reattachment processes of the rotor blades separated by 2 – 3 pitches result in 19 dominant mode orders in the circumferential direction. As the tip clearance increases from 1%C to 2%C, the difference of tip flow structures in each blade passage is significantly weakened, and the dominant mode order of the disturbance is equal to the rotor blade-passing number. The pressure fluctuation is mainly caused by cross-channel tip leakage flow, and the aerodynamic excitation frequency exhibits evident broadband hump characteristics, which has been reported as a rotating instability phenomenon.

Numerical Investigation of the Excitation Characteristics of Contaminated Nozzle Rings

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient.

Interior noise prediction of inter-coach space of high-speed maglev trains based on wavenumber decomposition on aerodynamic excitation

Current research on noise and vibration control of high-speed maglev trains pays more attention to far-field noise, while the level of interior noise has a direct impact on the ride comfort and should be placed equal weight on. In this paper, inter-coach space, one of the main pressure fluctuation sources of a specific type of high-speed maglev train with a design speed of 600 km·h−1, is taken as the research object. The turbulent and acoustic components of wall pressure fluctuations (WPF) are separated based on a wavenumber-frequency analysis approach, and then each component is applied as different forms of source input to the vibroacoustic model, namely, finite element method-boundary element method (FEM-BEM) and statistical energy analysis (SEA) for low- and high-frequency ranges respectively, to investigate the contribution of both components to interior acoustic cavity in all frequency range. It can be seen quantitatively from the results that the amplitude of turbulent component is generally much higher than that of the acoustic one, but it can be vice versa when it comes to the interior response. The conclusion drawn in this paper are able to provide guidance for future researches on more targeted interior noise control of high-speed maglev trains.

Coupled modal characteristics of a bladed rotor bearing system under aerodynamic and rotor excitations: Modelling and numerical study

Bladed Rotor Bearing System is considered in the coupled vibration analysis among blades and the rotor system. The governing equations of motion are derived based on Lagrange’s equation, which accounts for the coupled vibrational modes. The model is discretised based on the Galerkin finite element method. A comparative analysis on the influence of uniform and pre-twisted blade configurations on the BRBS and on individual blades is carried out. Free vibration analysis for various blade geometry configurations is studied and results show that natural frequencies of the blades are reduced in the presence of pre-twist whereas the same is increased with double-taper. The Campbell diagram revealed the presence of frequency veering among the blades and rotor loci of natural frequencies for a specific blade configuration. The influence of aerodynamic and external excitations on the blades and the rotor, respectively, are considered in the forced response analysis, where the resulting effects of both the excitations on the individual blades and the BRBS for different blade configurations are studied.

Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation

Abstract Current operational considerations require steam turbines to operate in a more flexible way, with more frequent and faster start-up and an increasing part-load operation. For very low mass flowrates, the interaction of highly separated flow with the high-speed rotor blades causes windage flow. This type of flow is characterized by increased temperature and highly unsteady flow, which forms vortex structures that rotate at a fraction of the rotor speed. If their magnitude is sufficiently high and the frequency is close to the blade eigenfrequency, non-synchronous vibration (NSV) can be induced. In this paper, low-flow turbine operation is investigated using a three-stage turbine rig that features an instrumentation concept focused on capturing aerodynamic and aeroelastic phenomena. Extensive steady probe, unsteady pressure, and tip-timing measurements are utilized. The experimental scope covers a wide range of operating points in terms of rotational speed and mass flowrates. Low-flow regimes are detected by a reversal in torque and increase in temperature. Unsteady measurements during transient operation identified large-scale vortical flow structures rotating along the circumference, so-called rotating instabilities (RIs). The onset, growth, and breakdown regimes of RI are characterized for different low-flow conditions. The quantitative characteristics of RI with regard to nodal diameter and rotational speed are derived by a cross-correlation of multiple unsteady sensors. The blade vibration measurements show a moderate structural response from unsteady aerodynamic excitation, indicating no significant NSV occurring in the present experimental setup. Later in the study, an acoustic excitation system has been applied to trigger a locked-in NSV without interrupting the coherent flow structures. From that, significant blade response has been observed, revealing a high degree of mistuning and damping of the rotor blading.

Modular approximate discrete modeling for blisk system with triple closed-loop equivalence method

At present, the lumped-parametric model is often used in the preliminary design of bladed disks. However, the lack of systematic modeling methods leads to high errors. In order to develop the systematic modeling method and improve the equivalence accuracy, this paper considers the comprehensive equivalence from the aspects of natural characteristics, transient forced responses, and steady-state forced responses under aerodynamic excitations. This paper includes two novelties. First, based on the modular equation of blisk system, an approximate discrete model is derived for computational efficiency. Second, a triple closed-loop equivalence method with modal weight optimization is developed innovatively for optimal equivalence parameters. The method can significantly improve the accuracy of element parameters in the lumped-parametric model and achieve the comprehensive equivalence to actual blisk. Compared with the existing equivalence method, the average errors of natural frequencies in the whole mode interval and in the high-density mode interval are reduced by 41.75 % and 36.76 %, respectively. The maximum and average displacement errors of the transient response are reduced by 51.76 % and 58.98 %, respectively. Furthermore, vibration characteristics of the mass and stiffness mistuned blisks are analyzed under traveling wake excitation during acceleration and deceleration processes by approximate discrete model and determined parameters.

Experimental and numerical investigations on non-synchronous vibration and frequency lock-in of transonic compressor rotor blades

Non-synchronous vibration (NSV) problems in axial compressors are challenging and frequently result in high vibration stress or structural failure within the frequency lock-in region. A deeper understanding of the lock-in phenomenon in NSV is necessary to improve blade reliability and safety. In this study, an experiment was conducted on a multistage transonic axial compressor to obtain frequency lock-in characteristics. The enforced motion of the flexible blade simulation method was used to study the frequency lock-in mechanism between blade vibration and tip unstable flow. The results showed that the aerodynamic frequency characteristic changed from a broadband spectrum to a distinct frequency peak as the NSV onset. The nonlinear vibration pattern could maintain the limited cycle oscillation for 26 s. The vibration stress of the frequency locked-in case was approximately 19 times that of the frequency unlocked one. The pressure fluctuations generated by the large-scale radial separation vortex structures were stronger than those of the tip leakage flow, and the third-order harmonic frequency of the circumferential instability flow was close to the first-order bending model natural frequency. The periodic shedding and reattachment process of flow separation provided the initial non-synchronous aerodynamic excitation source. The frequency lock-in phenomenon occurred at a maximum vibration amplitude of 2 % and 3 % tip chord length. The tip unstable flow characteristics were consistent and entirely dominated by blade vibration.

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

Effects of tip clearance on non-synchronous aerodynamic excitation of compressor rotor blades

The unstable tip flow of compressor rotor may cause the aeroelastic problems, inducing the non-synchronous vibration with high amplitude level, which has a significant effect on blade high cycle fatigue and safety. In order to investigate the effects of tip clearance on non-synchronous aerodynamic excitation of compressor rotor blades, the full annular numerical simulations were conducted for the unsteady flow field of a 1.5-stage compressor under near stall conditions. The frequency characteristics of non-synchronous aerodynamic excitation and tip unstable flow structure were analysed for different tip clearances (0.5%C, 1.0%C, 2.0%C, and 3.0%C). The results showed that the frequency and amplitude are strongly influenced by the tip clearance size. For 0.5%C tip clearance, the main frequency of non-synchronous aerodynamic excitation is the low-frequency aerodynamic excitation frequency, which is mainly caused by tornado-like vortex in the tip suction side, the dominant aerodynamic disturbance mode number is 19. For 2.0%C and 3.0%C tip clearance, the dominant aerodynamic disturbance mode number is 47, and the main aerodynamic excitation frequency is high frequency non-synchronous aerodynamic excitation frequency, mainly caused by the shedding vortices propagating circumferentially at the blade tip, exhibiting the feature of “rotating instability”.

Low-Engine-Order Forced Response Analysis of a Turbine Stage with Damaged Stator Vane.

A damaged stator vane can disrupt the circumferential symmetry of the design flow for turbine assemblies, which can lead to a low-engine-order (LEO) forced response of rotor blades. To help engineers be able to better address sudden vane damage failures, this paper conducts a mechanism analysis of the LEO forced response of rotor blades induced by a single damaged vane using an in-house computational fluid dynamic code (Hybrid Grid Aeroelasticity Environment). Firstly, it is found that the damaged vane introduces a family of LEO aerodynamic excitations with high amplitudes by full-annulus unsteady aeroelastic simulations of a single-stage turbine. In particular, the LEO forced response of the rotor blades excited by 3EO is 2.01 times higher than the resonance response excited by vane passing frequency, and the LEO resonance risk of the rotor blades is greatly increased. Then, by analyzing the flow characteristics of the wake and potential field of the stator row with a damaged vane, the localized high transient pressure in the notch cavity and the radial redistribution of the secondary vortex at the stator exit are the main sources of the low-order harmonic components in the flow field. Importantly, the interaction mechanisms in two regions with high LEO excitation amplitude on the rotor blade surface are revealed separately. Finally, an evaluation and comparison of a single damaged vane in terms of aerodynamic performance and LEO forced response was carried out. The results of this paper provide a good theoretical basis for engineers to effectively control the resonance response of rotor blades caused by a damaged stator vane in turbine design.

Dynamical responses and analysis of rotor-nacelle systems subjected to aerodynamic and base excitations

Dynamical responses and analysis of rotor-nacelle systems subjected to aerodynamic and base excitations

Improved Predictive Model of Drivers’ Subjective Perception of Vehicle Reaction under Aerodynamic Excitations

Improved Predictive Model of Drivers’ Subjective Perception of Vehicle Reaction under Aerodynamic Excitations

Anti-vibration Design of the Civil Aircraft’s Horizontal Tail Trailing Edge Compartment

The horizontal tail trailing edge compartment is a vital component of civil aircraft, situated between the horizontal tail beam and elevator. Its primary function is to connect the elevator and meet the aerodynamic sealing requirements of the unflapped elevator, and to transfer the aerodynamic and inertial load of the elevator to the outboard wing box of the horizontal tail in concentrated form. Under aerodynamic or other excitation, the horizontal tail trailing edge compartment may experience vibration, increasing the risk of structural damage. This study aims to enhance the anti-vibration capability of the horizontal tail trailing edge compartment via parametric finite element analysis. This analysis examines various design elements of the horizontal tail end cabin and compares the first-order modal frequency to deduce the influence of factors on the stiffness. The results provide a reference for the anti-vibration design of the horizontal tail trailing edge compartment in civil aircraft.