Improvement of sound atmosphere in the compartment of construc-tion machine

Noise inside the compartment of construction machine makes the operator feel annoyed and exhausted due to the unwanted component of noise. This paper deals with the treatment of sound inside the compartment of construction machine to make the sound atmosphere desirable for the operator. The main cause of annoyance due to the exposure of noise is the peaky engine order components. This paper provides the method to reduce annoyance for the operator inside by the reduction of peaky components.

ANALYSIS OF TRANSONIC BLADEROWS WITH NON-UNIFORM GEOMETRY USING SPECTRAL METHOD

Turbomachinery blade rows can have non-uniform geometries due to design intent, manufacture errors or wear. When predictions are sought for the effect of such non-uniformities, it is generally the case that whole assembly calculations are needed. A spectral method is used in this paper to approximate the flow fields of the whole assembly but with significantly less computation cost. The method projects the flow perturbations due to the geometry non-uniformity in an assembly in Fourier space. Only one passage is required to compute the flow perturbations corresponding to a certain wave-number of geometry variation. The performance of this method on transonic blade rows is demonstrated on a modern fan assembly. Low and high engine order geometry non-uniformity (e.g. “saw-tooth” pattern) are examined. The non-linear coupling between the flow perturbations and the passage-averaged flow field is also demonstrated. Pressure variations on the blade surface and the potential flow field upstream of the leading edge from the proposed method and the direct whole assembly solutions are compared. Good agreement is observed on both quasi-3D and full 3D cases. A lumped approach to compute deterministic fluxes is also proposed to further reduce the computational cost of the spectral method. The spectral method is formulated in such a way that it can be easily implemented into an existing harmonic flow solver by adding an extra source term, and can be used as an efficient tool for aeromechanical and aeroacoustics design of turbomachinery blade rows.

Forced Response Excitation of a Compressor Stator Owing to Shock Wave Induced by Adjacent Rotor Blade

The accurate prediction of high cycle fatigue (HCF) is becoming one of the key technologies in the design process of state-of-the-art axial compressors. If they are not properly designed, both rotor blades and stator vanes can be damaged. There are two main factors to cause HCF. One is low engine order (LEO) and the other is high engine order (HEO) excitation by fluid force associated with adjacent rotor-stator interaction. For the front stages of axial compressors for power generations and aero engines, the inlet Mach number of a rotor tip typically exceeds the speed of sound and strong shock waves tend to be induced. This can be the source of HEO excitation fluid force, and adjacent stator vanes are sometimes severely damaged. Thus, the aim of this study is to establish an efficient method for predicting the vibration response in this type of problem with high accuracy. To achieve this, numerical investigations are carried out by one-way fluid structure interaction (FSI) simulation. To validate the accuracy of FSI simulation, experiments are also conducted using a gas turbine engine for power generation. In the experiment, the vibration level is measured with strain gauges mounted on the surface of stator vanes and the data are compared with the predicted results. In the first part of the study, efficient prediction methods of excitation fluid force on the stator vane are investigated by time transformation (TT) and harmonic balance (HB) methods. Their accuracies are evaluated by comparing the results with those calculated by transient rotor stator (TRS) simulation whose pitch ratio is one between rotor and stator computational domains. It is found that the TT method can accurately predict the excitation fluid force with lower computation load even when there are pitch differences between rotor and stator regions. In the second part of the study, forced response analyses are carried out using the excitation fluid force obtained in the unsteady flow simulation. To obtain the total damping of the system, both hammering test and flutter simulations are carried out. Computed results are validated with experimental data and it is found that the predicted vibration level is in good agreement with experimental results. Through this study, the effectiveness of one-way FSI simulation is confirmed for this type of forced response prediction. By utilizing the combination of efficient unsteady computational fluid dynamics (CFD) methods and harmonic response analysis, vibration amplitude can be predicted accurately and efficiently.

On the Forced Response Predictions and Life Improvements of an Industrial Axial Compressor Rotor Blade

Improvements made to the high cycle fatigue life of an industrial compressor rotor blade for tip active modes through aerodynamic design changes and aero-mechanical assessments are presented in this paper. Typical aero-mechanical computations involved utilising an in-house linear-harmonic solver to compute the aero damping. In parallel, a novel hybrid model with whole-anulus domain for the blade rows of interest followed by a single passage domain for the rest of the compressor was used to compute the modal forcing. In addition to the standard blade passing resonances, low engine order excitations due to vane number differences, were analysed. This was achieved within a time frame consistent with the product design cycle by using TurboStream, a GPU based non-linear time domain unsteady flow solver. The excitation due to low engine order resonance was found to be influenced by a harmonic of upstream blade passing frequency. When considering a design change targeting HCF life, the calculated reserve factors showed significant improvements for the tip modes of interest. The subsequent engine tests carried out with tip timing agreed closely with the predictions thus validating not only the design but also the forced response prediction process.

Single Nodal Diameter Excitation of Turbine Blades: Experimental and Theoretical Study

Validating simulation results of vibrating turbine blades relies on measurements of realistic or academic cyclic structures on special test rigs. In real operation the blades are excited mainly by aerodynamic forces. For measurements of blade vibration on special test rigs, the excitation should be well known. It is desirable to use excitation spectra that consist of only a few engine order excitations. Especially for nonlinear systems, unwanted excitation orders can possibly lead to nonlinear effects which may interfere with the measurement. To separate different engine orders, an innovative electromagnetic excitation device was developed at the institution to overcome the aforementioned problems. The excitation force spectrum is controlled by a variable air gap over the circumference between device and blade. Any desired engine order excitation can be realized. Additionally, by varying the devices coil current in a harmonic fashion, frequency sweeps at constant speed can be performed. In this paper an extensive study of the excitation force spectrum of the device is conducted. Therefore, theoretical investigations of the expectable spectrum are given under simultaneous variation of air gap geometry and excitation current. These predictions are then validated by experiments featuring a small, academic bladed disk. The vibrations of the blades are measured. The device promises to create well predictable and controllable excitation force spectra which will improve the validation strategy in particular of non-linear simulation tools for the prediction of turbine blade vibrations.

The Effects of Gravity on the Response of Centrifugal Pendulum Vibration Absorbers

This paper describes the effects of gravity on the response of systems of identical, cyclically arranged, centrifugal pendulum vibration absorbers (CPVAs). CPVAs are passive devices composed of movable masses suspended on a rotor, suspended such that they reduce torsional vibrations at a given engine order. These absorbers are becoming prevalent in automotive powertrain components in order to expand fuel-efficient engine operating conditions. Gravitational effects acting on the absorbers can be important for a horizontal rotor/CPVA system spinning at relatively low rotation speeds, for example, during engine idle conditions. The main goal of this investigation is to predict the response of a CPVA/rotor system in the presence of gravity. A linearized model which includes the effects of gravity and an order n torque acting on the rotor is analyzed by exploiting the cyclic symmetry of the system. The results show that the N absorbers respond in one or more groups, where the absorbers in each group respond with identical waveforms but shifted phases. The number of groups depends on the engine order n and the ratio Nn. It is shown that there are special resonant effects if the engine order is n = 1 or n = 2, the latter of which is particularly important in applications. In addition, it is shown that for N > 1 the rotor response is not affected by gravity, due to the symmetry of the gravity effects. The analytical predictions are verified by direct simulations of the equations of motion.

A new bladed assembly simulator and an improved two-parameter plot method for blade tip-timing numerical simulations

The blade tip-timing measurement technique is presently the most promising technique for monitoring the blades of axial turbines and aircraft engines in operating conditions. Due to the high cost of experimental simulations of blade tip-timing–based condition monitoring methods, a numerical simulator for the vibrational behavior of bladed assemblies can be helpful for researchers interested in this field. So far, in most of the numerical simulators, the centrifugal effect of rotational speed on the natural frequencies is neglected. In this study, a new bladed assembly considering the centrifugal effect of the rotational speed for blade tip-timing numerical simulations is proposed. Moreover, an improvement in the engine order estimation algorithm in a two-parameter plot method is accomplished. In the assembly, blades are assumed to be cantilevered Euler–Bernoulli beams coupled together using linear springs. The finite element method is used to extract mass and stiffness matrices from differential equations of the system. By using the two-parameter plot method, the engine order of the excitation is detected. To examine the performance of the algorithm, Monte–Carlo simulation is implemented. The new simulator fulfills both cyclic symmetry and increase in the natural frequencies with increase in rotational speed. Engine order estimation with the new formulation in the two-parameter plot method is accurate. Hence, the new simulator and formulation for two-parameter plot method are reliable for numerical simulations.

Analysis of Nonlinear Modal Damping Due to Friction at Blade Roots in Mistuned Bladed Disks

A method is proposed to analyze the modal damping in mistuned bladed-disk with root joints using large finite element models and the detailed description of frictional interactions at contact interfaces. The influence of mistuning on the dissipated energy for different blades on a bladed-disk and the modal damping factors for different vibration levels for any family of modes can be investigated. The dissipated energy and damping factors due to microslip are simulated by multitude of surface-to-surface elements modeling the friction contact interactions at root joints. The analysis is performed in the time domain, and an original reduction method is developed to obtain the results with acceptable computational times. The model reduction method allows the calculation of the modal damping of the mistuned assembly by evaluation of the energy dissipated at root joint of each individual blade using small parts of bladed disk sectors. The dependency of modal damping factor on blade mode shapes, engine-order excitation numbers, nodal diameter numbers, and vibration amplitudes is studied and the distributions of amplitude and dissipated energy on the mistuned bladed-disk are investigated using a realistic blade disk model.

The effect of assembly and static unbalance on reaction wheel assembly bearing harmonics

Reaction wheel assemblies (RWA) are well-known major sources of microvibrations, whilst they have been studied thoroughly and many disturbance types can be reasonably modelled, bearing disturbances and how their amplitude evolves with the RWA rotational speed are not at the same level of confidence. Whilst studies have been carried out, many of the test rigs used do not truly show the bearing harmonic development, either due to interference from other disturbances such as structural modes or are not representative of an RWA. This study aims to design and validate a test rig which alleviates those issues by moving the resonance frequencies out of a range of interest and isolating the motor disturbances. Using this test rig, it was possible to observe many engine order development without any inference and start to investigate some of the effects some manufacturing parameters can have. The two studied and discussed in this paper were the effect of reassembly and static unbalance. Investigating the microvibration signature at different levels ranging from a top-down to individual harmonics it showed a clear significant variation between disturbance amplitudes.