Rotating Test Rig Research Articles

Study on the prediction of high-speed rotary lip seal wear in aero-engine based on heat-fluid-solid coupling

PurposeThis paper aims to investigate the effect of frictional heat on the wear of high-speed rotary lip seals in engines.Design/methodology/approachIn this research paper, the authors focus on the high-speed rotating lip seal of aircraft engines. Using the hybrid lubrication theory, a thermal-fluid-solid coupled numerical simulation model is established to investigate the influence of parameters such as contact pressure distribution, temperature rise and leakage rate on the sealing performance under different operating conditions. By incorporating the Rhee wear theory and combining simulation results with experimental data, a method for predicting the wear of the rotating seal lip profile is proposed. Experimental validation is conducted using a high-speed rotating test rig.FindingsThe results indicate that as the speed increases, the rise in frictional heat leads to a decrease in the sealing performance of the lip seal contact region. The experimental results show a similar trend to the numerical simulation results, and considering the effect of frictional heat, the predicted wear of the lip seal profile aligns more closely with the actual wear curve. This highlights the importance of considering the influence of frictional heat in the analysis of rotating seal mechanisms.Originality/valueThis study provides a reference for the prediction of wear profiles of engine high-speed rotary lip seals.

Experimental Vibration Data in Fault Diagnosis: A Machine Learning Approach to Robust Classification of Rotor and Bearing Defects in Rotating Machines

This study builds upon previous research that utilised a vibration-based machine learning (VML) approach for diagnosing rotor-related faults in rotating machinery. The original method used artificial neural networks (ANN) to classify rotor-related faults based on optimised vibration parameters from the time and frequency domains. This study expands the application of this vibration-based machine learning approach to include the anti-friction bearing faults in addition to the rotor faults. The earlier suggested vibration-based parameters, both in time and frequency domains, are further revised to accommodate bearing-related defects. The study utilises the measured vibration data from a laboratory-scale rotating test rig with different experimentally simulated faults in the rotor and bearings. The proposed VML model is developed for both rotor and bearing defects at a rotor speed that is above the first critical speed. To gauge the robustness of the proposed VML model, it is further tested at two different rotating speeds, one below the first critical speed and the other above the second critical speed. The paper presents the methodology, the rig and measured vibration data, the optimised parameters, and the findings.

Machine Learning Techniques for Multi-Fault Analysis and Detection on a Rotating Test Rig Using Vibration Signal

Machine health monitoring of rotating mechanical systems is an important task in manufacturing engineering. In this paper, a system for analyzing and detecting mounting defects on a rotating test rig is developed. The test rig comprises a slender shaft with a central disc, supported symmetrically by oscillating ball bearings. The shaft is driven at constant speed (with tiny variations) through a timing belt. Faults, such as the translation of the central disc along the shaft, the disc eccentricity, and defects on the motor reducer position or timing belt mounting position, are imposed. Time and frequency domain features, extracted from the vibration signal, are used as predictors in fault detection. This task is modeled as a multi-class classification problem, where the classes correspond to eight health states: one healthy and seven faulty. Data analysis, using unsupervised and supervised algorithms, provides significant insights (relevance of features, correlation between features, classification difficulties, data visualization) into the initial dataset, a balanced one. The experiments are performed using classifiers from MATLAB and six feature sets. Quadratic SVM achieves the best performance: 99.18% accuracy for the set of all 41 features extracted from X and Y accelerometer axes, and 98.93% accuracy for the subset of the 18 most relevant features.

On the study of vortex-induced vibration of a straked pipe in bidirectionally sheared flow

Helical strakes are widely used to suppress vortex-induced vibration (VIV) in ocean engineering. However, the VIV response and suppression efficiency of the straked pipe are unclear under the recently discovered bidirectionally sheared flow field. Experiments on vortex-induced vibration for a flexible pipe with three kinds of helical strakes were carried out in an ocean basin. The bare pipe model was 28.41mm in diameter and 7.64m in length. Three kinds of helical strakes with different pitch/height (17.5D/0.15D, 17.5D/0.25D,and 17.5D/0.35D) were applied. The test was performed on a rotating test rig to simulate bidirectionally sheared flow conditions. Fiber Bragg Grating (FBG) strain sensors were arranged along the test pipe to measure bending strains, and the modal analysis approach was used to determine the VIV response. The reduced velocities based on the tested first natural frequency of the bare pipe in water reached 30.79. The cross-flow and in-line VIV amplitudes, VIV suppression efficiency, and fatigue damage are presented in this article. The results showed that the helical strakes can suppress bidirectionally sheared flow-induced VIV significantly at a high reduced velocity regime with fatigue damage suppression efficiency over 99% in the CF and IL directions, but cannot suppress the in-line initial displacement, which was also found in previous studies as a drawback of helical strakes.

Influence of honeycomb structures on labyrinth seal aerodynamics

Shroud cavities in aero engines are typically formed by a labyrinth seal between the rotating turbine shroud and the stationary casing wall. To mitigate rub-in and reduce weight, the casing often features honeycomb structures above the rotor seal fins. In this paper, the aerodynamic performance of such honeycomb structures is experimentally investigated using a rotating test rig featuring both smooth and honeycomb-tapered casing walls. Measurements show that the discharge coefficient decreases for the honeycomb configuration while losses and subsequent windage heating of the flow increase. A variation in rotational speed reveals additional sensitivities to the local flow field in the swirl chamber. Numerical simulations are conducted and validated using the experiments. A good agreement between the prediction and measurements of the jet via the evolution of pressure across the sealing fins is identified. In contrast, the prediction of losses and integral parameters reveals larger deficits. Empirical correlations from available literature satisfactorily predict the leakage mass flow rate if rotation is low and if the casing is smooth. High rotation and the presence of honeycombs, however, prove challenging and reveal the potential for further improvements. We propose a simple a-posteriori correction that can capture the effect of honeycomb structures on seal discharge by accounting for changes in momentum and flow area.

Experimental investigation of vortex-induced vibration of a flexible pipe in bidirectionally sheared flow

The existence of a bidirectionally sheared flow field caused by internal solitary waves has recently been confirmed according to a field survey in the South China Sea. A model test of a tensioned flexible pipe in bidirectionally sheared flow was performed in an ocean basin. The model was 28.41mm in diameter and 7.64m in length. The purpose of the model test was to understand the response performance and obtain benchmark data of vortex-induced vibration (VIV) in bidirectionally sheared flow. The test was performed on a rotating test rig to simulate bidirectionally sheared flow conditions. Fiber Bragg Grating (FBG) strain sensors were arranged along the test pipe to measure bending strains, and the modal analysis approach was used to determine the VIV response. Reduced velocities based on the tested first natural frequency in water reached 30.79. The cross-flow and in-line VIV amplitudes, response frequencies in statistics and time-domain analysis, traveling wave characteristics, phase synchronization and trajectories are presented in this article. The maximum root mean square (RMS) VIV amplitudes in the test reached 0.51 diameters and 0.18 diameters in the cross-flow and in-line directions, respectively. A relative low Strouhal number of 0.10 was found in the CF direction.

Theoretical and experimental evaluations of pre-swirl rotor-stator system with inner seal bypass configuration for turbine performance improvement

Pre-swirl system has strong potential to improve the cooling performance and service life of high-pressure turbine rotor blades in gas turbine engines. This study is to evaluate and improve the temperature drop and power consumption characteristics of the pre-swirl system with multi-in and multi-out seal flow by theoretical and experimental analysis. Then, a high-speed rotating test rig of the pre-swirl rotor-stator system is established, considering the inner seal by-pass configuration to prevent the flow of hot gas into the pre-swirl cavity. In addition, the rotor-stator domain parameters in the pre-swirl system test rig are accurately measured at high-speed operating conditions. Three experimental schemes of pre-swirl systems are proposed for comparison under different operating conditions. The experimental results show that the temperature drop of the prototype pre-swirl system is in the range of 9.28–20.78 K, with the power consumption of the system ranging between −0.23 and −6.67 kW and the system pressure ratios being around 1.3–1.9. Because of the inner seal inflow ratio ranging within 0–15%, the system temperature drops for the improved pre-swirl system built-in inner seal by-pass passages notably reach a value between 12.12 K and 25.54 K with an average system power consumption within −0.41 to −8.21 kW. Thus, the improved pre-swirl system arrangement has dual advantages of a higher cooling effect and lower power consumption.

Deposition Pattern Analysis on a Fouled Multistage Test Compressor

Abstract Compressor fouling is one of the main causes of gas turbine performance degradation. Microsized particles adhere to the blade surfaces increasing the surface roughness and modifying the airfoil shape. In this work, the contamination of the Allison 250 C18 multistage compressor engine with four sorts of micrometric dust has been provided. The tests were performed changing the relative humidity (RH) at the compressor inlet and the unit rotational speed. After each test, a photographic inspection of the internal fouled parts has been realized and the digital pictures have been analyzed employing an image processing package. The deposit's build-up of stator vanes and rotor blades has been postprocessed and the most affected regions of each compressor stage have been highlighted. Besides, a numerical simulation of the machine has been performed. The numerical flow field has been used to highlight the blade regions, which show the most favorable conditions for particle deposition. A theoretical model has been applied to the flow field to simulate the particle deposition. The combination of the deposition model with the results of the numerical simulations gives the chance to better understand the experimentally founded deposition patterns. Those results have been finally compared to the pictures of the patterns. The possibility to detect and measure the deposition patterns on a rotating test rig and the comparison with models and experiments gave the possibility to assess in detail the particle deposition phenomenon on a multistage axial compressor flow path.

Dynamic Analysis and Experimental Research on the Cantilever High Speed Rotor of Turbofan Engine

Taking a simulated low-pressure rotor of a turbofan engine as the research object, the dynamic characteristic calculation model of the simulated low-pressure rotor with hollow shaft and solid shaft was established respectively by using the finite element method. The first three order critical speeds and mode shapes of the rotor were calculated systematically. The dynamic balance test of the simulated low-pressure rotor and the research on the damping effect of the squeeze film damper were carried out on the high-speed rotating test rig, and the dynamic characteristic test was completed in the full speed range. The results show that the finite element results agree well with the experimental results. The rationality of the rotor’s hollow shaft structure and rotor dynamic design was verified. The research provides reference and technical support for structural design, dynamic design and experimental research of real low-pressure rotor in engine.

Influence of the limited room space on inlet conditions and fan operation at the rotating test rig

The limited space of the laboratory room allows maintaining the selected ambient air parameters in the required ranges. It can be, however, a source of many problems in the case of rotating test rigs that blow a large amount of air. The aim of the paper is to examine the influence of limited space and its shape on the working conditions of axial fans test stand. The focus was particularly on the conditions prevailing at the inlet to the test rig and their potential impact on the tested fan operation. The article presents the results of CFD simulations for two rooms of different volumes and the results of experimental measurements carried out for the smaller one. Good qualitative agreement between the simulations and the experiment was obtained. The limited space around the test rig causes the unsteadiness of the axial velocity profile and introduces an unsteady swirl at the inlet. This leads, in turn, to local changes in the angle of attack of the fan blades and the resulting consequences related to the off-design working conditions. The paper proves the need to minimise the effects of the induced airflow in the test room and proposes some methods to accomplish this task.

Analysis of Leaf Seal Leakage Performance Under the Influence of Manufacturing Variations Using Experiment and Computational Fluid Dynamics

Abstract In this paper, test data are combined with results from two different computational fluid dynamics (CFD) models to investigate the leakage performance of leaf seals. Experimental data are gathered for centric rotor position using a rotating test rig at various rotational speeds, inlet pressures, and preswirl velocities. The test results are compared to brush and labyrinth seal leakage data from previous studies and reveal elevated leakage rates of the leaf seal. As the tested leaf seals are subject to thermal leaf deformation from welding during the manufacturing process, the influence of geometry variations within the leaf pack on leakage performance is investigated with the help of numerical simulations. Both a fully resolved leaf model and a modeling approach based on porous media are used. The CFD models are validated based on pressure measurements within the up- and downstream coverplate gaps at three different radii. Both CFD models show good agreement with test data for different inlet parameters. A variation of cold clearance shows moderate influence on leakage and small clearances can be brought into context with hydrodynamic lift-up indicated by experimental leakage data. Much higher sensitivity on leakage mass flow is predicted for variations in leaf spacing at the leaf root and leaf tip. The latter is discussed as an explanation for the measured leakage of the test seal with its manufacturing variations, while the first quantitatively shows optimization potential at the design stage of leaf seals.

Consolidated results of the laboratory and full scale field validation of an active flap system

This article presents the consolidated results of a comprehensive validation campaign of a pneumatic active flap system (AFS) developed within the scope of the Induflap2 project [1] in a collaboration effort between Siemens Gamesa Renewable Energy A/S (SGRE), the Technical University of Denmark (DTU), and Rehau GmbH. The validation results presented herein include wind tunnel measurements, measurements in a rotating test rig under free atmospheric conditions, as well as the validation at full scale on a 4MW wind turbine with 130m rotor diameter (SWT-4.0-130). This article is of a summarizing character and the reader is referred to further literature where applicable. During the course of the project, several revisions of the AFS were developed and tested at different levels of fidelity. Along with the different variations of the AFS, the impact of variations of the geometric and material related design parameters were studied. Two of the latest revisions of the AFS were tested at full scale on a wind turbine. The measurements presented herein focus solely on the latest revision of the AFS (internally referred to as the FT008rev10 concept). The different tests and measurements were performed in the period from 2016 to 2019. During the full scale measurements, a wind speed dependent load impact between 5% and 10% was measured for the blade root flapwise bending moments, demonstrating thus a large potential for turbine loading adjustments to perform active load control on modern wind turbines.

Field testing of morphing flaps on a wind turbine blade using an outdoor rotating rig

Abstract In recent years, active flap devices on wind turbine blades have been shown to both reduce peak loads at the tower and extend blade fatigue life. Associated benefits include retrofitting existing tower infrastructure with longer and greater energy-producing blades whilst also extending service life of blades. In the current work, a novel wind turbine blade control method using morphing flaps has been successfully investigated and demonstrated using a scaled demonstrator mounted on an outdoor rotating test rig. Shape adaptive structures that remain conformal to the flow are increasingly referred to as morphing devices. As part of the INNWind.eu project, a novel morphing flap device was developed for a recently designed aerofoil. The proposed morphing flap comprises a light-weight carbon fibre laminate, 3D printed honeycomb core and a flexible silicone surface. A comprehensive test campaign using an outdoor rotating test rig under atmospheric conditions was carried out to assess the potential effectiveness. As shown by experimental data, the morphing flap provides good performance in terms of aerodynamic lift control of the blade and can provide dynamic load alleviation capability.

Aerodynamic and load control performance testing of a morphing trailing edge flap system on an outdoor rotating test rig

A testing campaign utilizing DTU’s outdoor rotating rig is described, where a novel morphing flap system developed in collaboration with the University of Bristol within the INNWIND.eu project has been evaluated and successfully demonstrated. In addition, the aerodynamic performance of ECN’s newly designed aerofoil has been evaluated in atmospheric conditions. The morphing wing is shown to achieve good performance in terms of aerodynamic lift control, and compares well with computational fluid dynamics predictions. Moreover, simple feed-forward controller implementations, also utilizing inflow sensors, show promising results in terms of dynamic load alleviation.

Identification of Dynamic Characteristics of Hybrid Bump-Metal Mesh Foil Bearings

The stability of oil-free high-speed turbo-machinery can be effectively improved by increasing the damping characteristic of the gas foil bearing (GFB). Novel hybrid bump-metal mesh foil bearings (HB-MFBs) have been previously developed. Prior experimental results show that the parallel combination of bump structure and metal mesh not only can improve the structure stiffness but also provide better damping property compared with the bump-type foil structure. To investigate the dynamic behavior of floating HB-MFBs and promote its application, this study measured the dynamic force coefficients of HB-MFBs on a rotating test rig. The vibrations of HB-MFBs with different mesh densities (40%, 32.5%, and 25%) and a generation І bump-type foil bearing (BFB) with similar size are measured under static and impact loads to estimate the bearing characteristics. Static load test results show that the linear stiffness decreases when the air film is generated (from 0 rpm to 20 krpm) but increases gradually with speed (from 20 krpm to 30 krpm, and 40 krpm). Moreover, the dynamic force coefficients of HB-MFBs indicate the significant influence of metal mesh density on bearing dynamic characteristics. The growth in block density increases the dynamic stiffness and damping coefficients of bearing. The comparison of HB-MFB (32.5% and 40%) and BFB emphasizes the good damping characteristics of HB-MFB.

On- and off-design performance of a model rotating turbine with non-axisymmetric endwall contouring and a comparison to cascade data

ABSTRACTNon-axisymmetric endwalls in turbine stages have shown to be a robust method to improve the performance of turbines in both power generation and aero-derivative applications. Non-axisymmetric endwalls target the control of secondary flows and are designed using detailed computational fluid dynamics coupled with a variety of optimisation algorithms and utilising a number of objective functions according to the engine company or researcher's preference. These numerical predictions are often backed up by detailed measurements in linear and annular cascades and later proven in full-scale engine tests. Relatively little literature is available describing their performance in rotating test rigs or at conditions other than design, apart from that of the authors. This study comprehensively revisits the low-speed, model turbines used in the earlier study, replacing all of the 5-hole probe data with more accurate results and additional hot-film measurements. These results together with computational fluid dynamics solutions are used to show the success of the method across a large incidence range and to compare to earlier cascade results for a similar endwall and blade profile to establish the usefulness of cascade testing in this application. In addition, a comparison to two other off-design studies is made. Results indicate that the endwalls successfully improve the rotor total isentropic efficiency at all test conditions and that the improvement increases with increased turning in the blade row, from 0.5% to 1.8% across the incidence range. The results also compare well to the estimation of isentropic efficiency improvement that can be drawn from the cascade testing which stands at 1.55%.

Fault diagnosis of tilting-pad type fluid film bearings in high-speed rotating machinery

Of all fluid film bearing types, tilting pad bearings offer the optimal rotordynamic stability due to their excellent stiffness and damping characteristics. Due to the reduction in cross-coupling stiffness, tilting pad bearings are ideal for use in high-speed and high-load turbomachineryapplications, such as industrial compressors and steam/gas turbines. In this investigation, we propose the method to diagnose the main failure mode of tilting pad journal bearings such as babbitt metal wear and pivot wear in bearing pads. Various experimental cases for bearing wearwere precisely implemented through a high-speed rotating test rig operating at 10,200 rpm. The vibration and temperature data were obtained through a condition monitoring system and various features from shaft vibration, bearing metal and lubrication temperature data were extracted for the fault diagnosis. In this study, we have shown that even defects due to the abrasive wear of fluid film bearings including general rotor faults, such as unbalance, misalignment and rubbing, can be accurately diagnosed.

High Speed Visualizations of oil Jet Lubrication for Aero-engine Gearboxes

Abstract Augmenting gearing systems efficiency is a key issue in developing innovative aero-engines with low specific fuel consumption. The transmission system directly affects the engine overall efficiency, therefore it is essential maximizing its performance. In high speed applications fluid-dynamic losses become predominant and are directly connected to the lubrication method. Oil jet systems are generally used in order to achieve a proper cooling and lubrication of tooth surface. A novel rotating test rig was exploited for investigating oil jet lubrication by means of high speed visualizations. An oil jet impinging radially on a single spur gear was generated by a spray-bar, assessing which parameters affect the oil jet behavior.

Application of wireless power transfer technologies and intermittent energy harvesting for wireless sensors in rotating machines

Battery-powered wireless sensor networks have been extensively deployed in condition monitoring and structural health monitoring systems, but the performance of wireless sensors are limited by battery capacity and difficulty of application in rotating machines. In this paper, a variety of commercial wireless charging solutions and coil-shaft configurations for magnetic coupling are compared, having in mind of the application of continuously charging wireless sensors on rotating machines. For the co-axial configuration of the transmitter coil and the receiver coil, a Qi standard compliant wireless charging kit and a custom charging circuit are successfully applied to charge wireless sensors on small rotating test rigs. In order to harvest and store intermittent energy input from the wireless power source, a prototype receiver circuit using a supercapacitor and low-dropout regulator is designed and validated. Based on the prototype circuit, the radial configuration of single transmitter coil and multiple receiver coils is demonstrated for wireless power transfer to the sensor nodes on the drivetrain of a small wind turbine test rig.

Heat Transfer Investigation on an Internal Cooling System of a Gas Turbine Leading Edge Model

A scaled up test model simulating a realistic leading edge cooling system of a high pressure gas turbine blade was designed with the aim of performing heat transfer measurements in static and rotating conditions.The test model is composed by a trapezoidal supply channel which feeds three large racetrack holes, generating coolant impingement on the internal concave leading edge surface. Four big fins allow to confine the impingement jets impact zones. Air is then extracted through 4 rows of 6 holes each, two of showerhead (SH) and two of film cooling (FC). The test model is installed on a rotating test rig, which allows to reach jet Reynolds numbers (Rej) up to 40000 and rotation numbers (Roj) up to 0.05. The effect of cross-flow in the supply channel is also considered.The heat transfer coefficient (HTC) distribution on the internal concave surface was evaluated by means of a steady state technique, using wide band thermochromic liquid crystals (TLCs) to measure the wall temperature and an electrically heated Inconel sheet to provide a constant heat flux to the investigated surface.This paper reports experimental results obtained in static conditions for Rej 10000 and 30000 and for two cross-flow cases representative of blade tip and hub sections. The effects of different mass flow extraction between pressure and suction side is also investigated by varying the mass flow rate through FC and SH holes.The effect of the coolant extraction holes geometry on the Nusselt number distribution is analyzed by comparing the experimental results, reported as 2D Nusselt number (Nu) maps, with a previous investigation on an analogous test model with similar impingement geometry. A CFD campaign was also carried out on the present test rig, exploiting a previously validated computational model. Both numerical and experimental results reveal that the effects of differentiated mass flow extraction and extraction area modification are secondary with respect to the effects of Rej and crossflow variation.