ARTICLE | doi:10.20944/preprints202208.0228.v1
Subject: Engineering, Energy & Fuel Technology Keywords: Wind power; Wind turbines; Aerodynamics; Differential Geometry; Airfoils; Blade Element Momentum Theory; BEMT; BEM; HAWT; Wagner rotor
Online: 12 August 2022 (07:53:19 CEST)
Purpose – Extend the Blade Element Momentum Theory (BEMT) such that rotors with pronounced cone and axis angle (tilt or yaw) can be calculated. Derive an equation for the speed ratio (lambda) as a function of Tip Speed Ratio (TSR), radius, blade, cone and axis angle. This converts the BEMT into an Unsteady BEMT or UBEMT. Present the Wagner rotor as one such rotor geometry. --- Methodology – Literature review and calculations. --- Findings – The UBEMT can be used to calculate highly unconventional rotor geometries. --- Research Limitations – Although the aerodynamic coefficients used in the UBEMT are from measurements in steady flow conditions, they can be used with success. --- Practical Implications – Also conventional Horizontal Axis Wind Turbines (HAWT) with noticeable cone and axis angle should be calculated with the UBEMT. The accuracy of power calculations of these HAWTs can be slightly improved. --- Originality – Analytic equations for rotors with cone and axis angle have barely been discussed.
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Hydrostatic; Blade guides; Bandsaw; Diamond blade; Natural stone; Sawing
Online: 24 February 2020 (12:23:56 CET)
In a bandsaw machine the blade guides provide additional stiffness and help to align the blade near the cutting region. Typically these are either in form of blocks made of carbide or ceramics or as sealed bearings. Abrasive particles, generated while cutting hard and brittle materials like natural stones, settle between the contact surfaces of the guides and the blade causing wear and premature failure. The hydrostatic guide system as presented in this work, is a contactless blade guiding method that uses force of several pressurized water jets to align the blade to the direction of the cut. For this investigation, cutting tests were performed on a marble block using a galvanic diamond coated bandsaw blade with the upper roller guides replaced by hydrostatic guides. The results show that the hydrostatic guides help to reduce the passive force while cutting to a constant near zero in contrast to the traditional guides. This also resulted in reduced surface roughness of the stone plates that were cut indicating a reduction in lateral vibration of the band. Additionally, it has also been shown that using hydrostatic guides the bandsaw blade can be tilted to counter the bandsaw drift opening opportunities for further research in active alignment control. This original research work has shown that the hydrostatic guide systems are capable of replacing and in fact perform better than state of the art bearing or block guides particularly for stone cutting applications.
TECHNICAL NOTE | doi:10.20944/preprints201911.0279.v1
Subject: Engineering, Mechanical Engineering Keywords: blade vibration; blade tip-timing; rotating stall; axial compressor; blade health monitoring; least squares; bladed disc dynamics
Online: 24 November 2019 (13:32:49 CET)
Complex blade responses such as a rotating stall or simultaneous resonances are common in modern engines and their observation can be a challenge even for state-of-the-art tip-timing systems and trained operators. This paper analyses forced vibrations of axial compressor blades, measured during the bench tests of the SO-3 turbojet. In relation to earlier studies conducted in ITWL with a small number of sensors, a multichannel tip-timing system let us observe simultaneous responses or higher-order modes. To find possible symptoms of a failure, blade responses in a healthy and unhealthy engine configuration with an inlet blocker were studied. The used analysis methods covered all-blade spectrum and the circumferential fitting of blade deflections to the harmonic oscillator model. The proposed modal solver can track the vibration frequency and adjust the engine order on the fly. That way, synchronous and asynchronous vibrations are observed and analysed together with an extended variant of least squares. The proposed approach helps to avoid common mistakes and saves a lot of work related to configuring the conventional solver.
ARTICLE | doi:10.20944/preprints202107.0077.v1
Subject: Engineering, Mechanical Engineering Keywords: high-temperature sensor; inductive sensor; blade tip timing; blade health monitoring
Online: 5 July 2021 (08:04:14 CEST)
Magnetic sensors are widely used in health management systems for turbomachinery, but their applications in the hot zone are limited due to the loss of magnetic properties by permanent magnets with increasing temperature. The paper presents and verifies models and design solutions aimed at improving the performance of an inductive sensor for measuring the motion of rotating objects operating at elevated temperatures (200-1000C), such as compressor and turbine blades. Physical, analog and mathematical models of the interaction of blades with the sensor were developed. A prototype of the sensor was made and its tests were carried out on the RK-4 rotor rig for the speed of 7000 rpm, in which the temperature of the sensor head was gradually increased to 1100C. The sensor signal level was compared to that of an identical sensor operating at room temperature. The heated sensor works continuously producing the output signal whose level does not change significantly. What is more, a set of six probes passed an initial engine test in an SO-3 turbojet. It was confirmed that the proposed design of the inductive sensor is suitable for blade health monitoring of the last stages of compressors, steam turbines as well as previous generation gas turbines operating below 1000C, even without a dedicated cooling system. In real-engine applications, sensor performance will depend on how the sensor is installed and the available heat dissipation capability
ARTICLE | doi:10.20944/preprints202009.0402.v2
Subject: Engineering, Control & Systems Engineering Keywords: MEFCA, Cost method; Turbine blade manufacturing; Environmental management accounting
Online: 15 March 2021 (13:06:43 CET)
It is often difficult to extract data on material and energy wates and related costs in the value chain of conventional production units. Many organizations are not fully aware of the actual cost of material and energy waste. For this purpose, advanced costing methods should be used. This study uses material and energy flow cost accounting to determine material costs, losses, and waste management. The case study of this research is the construction of turbine blades in Iran Power Plant Company. In this study, using the extracted data, the construction costs of turbine blades have been studied. The conventional method of making a turbine blade is the machining method, which we will see has a huge amount of wastes of materials and energy. By studying different methods, we will find that there is an alternative method called forging, which reduces losses and costs. Finally, the costs of the two methods are compared. Engineering economics techniques have also been used to compare two methods on a long-term planning horizon.
ARTICLE | doi:10.20944/preprints202012.0140.v1
Subject: Engineering, Automotive Engineering Keywords: Vertical Axis Wind Turbine; Wind Energy; Helical Blade; CFD
Online: 7 December 2020 (12:00:17 CET)
The global energy crisis has lead researchers explore other sources of energy like wind, resulting in a wide acceptance of wind turbines. Vertical axis wind turbines (VAWT) more suitable for small scale application in urban conditions than their horizontal-axis counterparts. A Helical bladed VAWT would reduce the ripple effect when compared to Straight bladed VAWT. The effect of the blade helix angle on the aerodynamic performance of VAWT using 3D numerical simulations is studied. Turbulence modelled using 4-Equation transition SST k-w model. Three different helix angles of 60, 90 and 120 of a 3 bladed VAWT operating across different tip speed ratios were studied. The 60 helical bladed VAWT was found to perform better than all other helical bladed and straight bladed VAWT. Standard deviation of the moment coefficient generated by a blade plotted against 360 of azimuth rotation revealed that the ripple effect on the shaft produced by cyclic loading of the straight blade is considerably reduced upon introduction of helix angle, with 120 helical blade giving lowest standard deviation. The analysis has been done for the percentage of power generated by each quartile of flow and the contribution of each section of the blade. A comparative study was also conducted between different helical bladed VAWT and straight bladed VAWT. Flow feature analysis also revealed the reasons behind secondary peaks and the performance improvement when tip speed ratio increases. Wake structure analysis and flow contours were also studied for a better understanding of the flow field.
ARTICLE | doi:10.20944/preprints201811.0394.v3
Subject: Engineering, Electrical & Electronic Engineering Keywords: marine current turbine; blade attachment; sparse autoencoder; softmax regression
Online: 12 February 2019 (09:59:09 CET)
The development and application of marine current energy are attracting more and more attention around the world. Due to the hardness of its working environment, it is important and difficult to study the fault diagnosis of a marine current generation system. In this paper, an underwater image is chosen as the fault-diagnosing signal, after different sensors are compared. This paper proposes a diagnosis method based on the sparse autoencoder (SA) and softmax regression (SR). The SA is used to extract the features and SR is used to classify them. Images are used to monitor whether the blade is attached by benthos and to determine its corresponding degree of attachment. Compared with other methods, the experiment results show that the proposed method can diagnose the blade attachment with higher accuracy.
REVIEW | doi:10.20944/preprints202207.0177.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: dip-coating; spin-coating; spray-coating; blade-coating; roll-coating
Online: 12 July 2022 (09:01:50 CEST)
In this review, several cost-effective thin-film coating methods which include dip-coating, spin-coating, spray-coating, blade-coating, and roll-coating are presented. Each method has its set of advantages and disadvantages depending on the type of application. Not all of them are appropriate for large-scale production due to their certain limitations. That is why the coating method should be selected based on the type and size of substrate including the resolution of the required thin-films. The sol-gel method offers several benefits, such as simplicity in fabrication, excellent film uniformity, the capacity to cover surfaces of any size and over vast areas, and a low processing temperature. Nevertheless, these coating methods are somewhat economical and well managed in low-budget laboratories. Moreover, the produced thin-films are homogeneous and have low-surface roughness. Furthermore, some other thin-film deposition methods such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) are also discussed. Since CVD is not restricted to line-of-sight deposition, a characteristic shared by sputtering, evaporation, and other PVD processes, many manufacturing methods favor it. However, these techniques require sophisticated equipment and cleanroom facility. We aim to provide the pros and cons of thin-film coating methods and let the readers decide the suitable technique for their specific application.
ARTICLE | doi:10.20944/preprints202004.0295.v1
Subject: Engineering, Mechanical Engineering Keywords: plenum fan; blade profile; static pressure; static efficiency; velocity distribution
Online: 17 April 2020 (08:22:49 CEST)
We successfully designed an optimized plenum fan with a three-dimensional, smooth, curved blade. The optimized model revealed that the static pressure in the channel had been increased uniformly and stably, and the flow separation at the leading edge was significantly reduced. To conclude, the three-dimensional blade stabilized the fluid flow, and the flow friction was reduced by suppressing the flow separation as much as possible so that both the static pressure and the static efficiency were clearly improved in comparison with those of the original model. The static efficiency, as a result, was improved by 6% compared with that of the original model.
ARTICLE | doi:10.20944/preprints201705.0146.v1
Subject: Engineering, Marine Engineering Keywords: power generation cycle; turbo machinery; turbine; compressor; blade; airfoil; noise
Online: 19 May 2017 (08:54:53 CEST)
A turbomachinery is essential part in the power generation cycle. But, it is main noise source to annoy workers and users and to make environmental problem. Thus it is important to reduce this noise for operating the power generation cycle. This noise is created by flow instability on rotor blade trailing edge. An airfoil that becomes a section of a rotor blade of a rotating machine is manufactured as a blunt trailing edge (TE) with a round or flatback shape rather than the ideal sharp TE shape for the purposes of producibility and durability. This increases the tonal noise and flow-induced vibration at low frequency owing to vortex shedding behind TE when compared with a sharp TE. In order to overcome this problem, this study investigates the oblique TE shape using numerical simulation. In order to do so, the flow was simulated using large eddy simulation (LES) and the noise was analysed by acoustic analogy coupled with LES result. Once the simulation results were verified using the flatback airfoil measurements of Sandia National Laboratories, numerical prediction was performed for airfoils modified to have oblique trailing edge angles of 60°, 45°, and 30° to analyse the flow and noise characteristics. From the simulation results for an airfoil having an oblique TE, it could be seen that the vortex shedding frequency moves in accordance with the oblique angle and that the vortex shedding noise characteristics change according to this angle when compared to the flatback TE airfoil. Therefore, it is considered that modifying the flatback TE airfoil to have an appropriate oblique angle can reduce noise and change the tonal frequency to a bandwidth that is suitable for mechanical systems.
ARTICLE | doi:10.20944/preprints201705.0122.v1
Subject: Engineering, Mechanical Engineering Keywords: morphing blade; adaptive geometry; computational fluid dynamics; fluid-structure coupling
Online: 16 May 2017 (13:06:29 CEST)
The concept of smart morphing blades, which can control themselves to reduce or eliminate the need for active control systems, is a highly attractive solution in blade technology. In this paper an innovative passive control system based on Shape Memory Alloys (SMAs) is proposed. On the basis of previous thermal and shape characterization of a single morphing blade for a heavy-duty automotive cooling axial fan, this study deals with the numerical analysis of the aerodynamic loads acting on the fan. By coupling CFD and FEM approaches it is possible to analyze the actual blade shape resulting from both the aerodynamic and centrifugal loads. The numerical results indicate that the polymeric blade structure ensures proper resistance and enables shape variation due to the action of the SMA strips.
ARTICLE | doi:10.20944/preprints202203.0238.v1
Subject: Engineering, Marine Engineering Keywords: Virtual Blade Model; Code extension; CFD modeling; Tidal turbine; Wind turbine
Online: 17 March 2022 (02:37:47 CET)
The Virtual Blade Model (VBM) is the implementation of the Blade element model (BEM). This was done by coupling the Blade Element Momentum theory equations to simulate rotor operation with the Reynolds Averaged Navier-Stokes (RANS) equation to simulate rotor wake and the turbulent flow field around it. Exclusion of actual geometry of blades causes lower computational cost (about 10 to 100 times). Also, due to simplifications in the meshing procedure, VBM is easier to set up than the models that consider the actual geometry of blades. One of the main unaddressed limitations of the VBM code was the constraint of modeling up to ten rotor zones within one computational domain. This paper provides a detailed and well-documented general methodology to develop a virtual blade model for simulation of ten-plus turbines within one computational domain to remove the limitation of this widely used and robust code. It is strongly believed that the technical contribution of this paper, combined with the current sky-rocketing advancement of available computational resources and hardware, would open the gates to simulate various engineering problems in the field of aerospace, clean energy, and many more.
ARTICLE | doi:10.20944/preprints202108.0273.v1
Subject: Engineering, Mechanical Engineering Keywords: compressor blade; fatigue life; shot-peening; x-Ray diffraction; residual stresses
Online: 12 August 2021 (11:03:28 CEST)
The work presents the results of numerical fatigue analysis of a turbine engine compressor blade, taking into account the values of initial stresses resulting from surface treatment - shot-peening. The values of the residual stresses were estimated experimentally using X-ray diffraction. The paper specifies the values of the residual stresses on both sides of the blade and their reduction due to the cutting through the blade - relaxation. The obtained values of the residual stresses were used as initial stresses in the numerical fatigue analysis of the damaged compressor blade, which is subjected to resonant vibrations of known amplitude. Numerical fatigue ε-N life analysis was based on the several fatigue material models: Manson’s, Mitchell’s, Baumel-Seeger’s, Muralidharan-Manson’s, Ong’s, Roessle-Fatemi’s and Median’s, and also on the three models of cyclic hardening: Manson’s, Xianxin’s, and Fatemi’s. Because of this approach, it was possible to determine the relationship between the selection of the fatigue material ε-N model and the cyclic hardening model on the results of the numerical fatigue analysis. Additionally, the calculated results were compared with the results of experimental research, which allowed for a substantive evaluation of the obtained results. These results are of great scientific and practical importance. The problem of determining the fatigue life of blades with defects operating under resonance vibrations is one of the original tasks in the field of fracture mechanics and experimental mechanics. The results obtained are of great importance in the aviation industry and can be used during engine maintenance and inspections to assess the suitability of blades with defects in terms of the needs of further work. This aspect of engineering maintenance is of great importance from the aircraft safety point of view.
ARTICLE | doi:10.20944/preprints202105.0027.v1
Subject: Engineering, Automotive Engineering Keywords: Pump as Turbine; Flow Unsteadiness; Pressure Pulsation; Blade Angle; Numerical Simulation
Online: 5 May 2021 (08:57:28 CEST)
The adoption of Pump as Turbines (PATs) both in small scale hydroelectric plants and water supply systems has brought different advantages, the most recognized being cost-effectiveness as compared to other hydroturbines. However, due to their lack of flow control ability, their intolerance to off-design operations constitutes one tough shortfall. Moreover, this technology’s newness leads to PAT flow dynamics still being ununderstood even to date. Therefore, this study intends to numerically investigate the mixed flow PAT’s pump mode flow dynamics for five operating conditions expanding from optimum (1QBEP) to deep part-load (0.41 QBEP) conditions. Moreover the effect of runner blade angle on the same has been investigated where three angles namely -2°, 0°, and 2° have been considered. PAT flow stability was found to deteriorate as the flow decreased, where associated pressure pulsation level worsened at different flow zones. In addition, the blade angle increase led correspondingly increasing flow unsteadiness and pressure pulsation levels, where the pulsation frequencies from rotor-stator interactions were dominant for most of flow zones. This study’s findings are of a crucial importance to both scientific and engineering communities as they contribute to thorough understanding of PAT flow dynamics.
ARTICLE | doi:10.20944/preprints201906.0108.v1
Subject: Engineering, Mechanical Engineering Keywords: Blade cooling; Gas turbine efficiency; TIT-pressure ratio correlation for optimal efficiency
Online: 12 June 2019 (15:36:03 CEST)
Modern gas turbines firing temperatures (1500-2000K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages -nozzle vanes and rotor blades- with a portion of the compressor discharge air, a practice that induces a penalty on the cycle thermal efficiency. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different TIT (turbine inlet temperature) and max (total turbine expansion ratio) with a realistically acceptable degree of approximation.. The calculations suggest that, at a given max, the TIT can be increased in order to reach higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher max and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at lower rather than higher max. The small penalty on cycle efficiency is compensated by lower plant cost. The results of our model agree with those of some previous much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate and low resource intensity of the corresponding numerical procedure: all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic, with no investigation on the effects of the different configurations on plant costs, so that future work addressing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.
ARTICLE | doi:10.20944/preprints201707.0007.v1
Subject: Engineering, Mechanical Engineering Keywords: axial fan; laser scanning vibrometry; wind tunnel; inlet cross-flow; blade vibration
Online: 5 July 2017 (04:22:10 CEST)
In thermal power plants equipped with air-cooled condensers, axial cooling fans operate under the influence of ambient flow fields. Under inlet cross-flow conditions, the resultant asymmetric flow field is known to introduce additional harmonic forces to the fan blades. This effect has previously been studied only numerically or using blade mounted strain gauges. For this study, Laser Scanning Vibrometry was used to assess fan blade vibration under inlet cross-flow conditions in an adapted fan test rig inside a wind tunnel test section. Two co-rotating laser beams scanned a low pressure axial fan, resulting in spectral, phase resolved surface vibration patterns of the fan blades. Two distinct operating points were examined, with and without inlet cross-flow influence. While almost identical fan vibration patterns were found for both reference operating points, overall blade vibration increased by 100% at low fan flow rate due to cross-flow, and by 20% at high fan flow rate. While numerically predicted natural frequency modes could be confirmed from experimental data as minor peaks in the vibration amplitude spectrum, they were not excited significantly by cross-flow. Instead, primarily higher rotation rate harmonics were amplified, i.a. a synchronous blade tip flapping was strongly excited at the blade pass frequency.
ARTICLE | doi:10.20944/preprints202107.0026.v1
Subject: Engineering, Control & Systems Engineering Keywords: smart sensor; multi-agent system; modular architecture; Blade Health Monitoring; system on chip
Online: 1 July 2021 (12:33:59 CEST)
Blade Health Monitoring (BHM) is often necessary in power plants and in aviation to prevent excessive blade vibration and cracks. This article proposes a network of blade tip timing sensors operated in a distributed BHM system. A number of cooperating agents is implemented in smart conditioning units which can autonomously operate in an adverse environment and communicate with other nodes via a serial interface. The project uses special versions of reduced instruction set chips that are able to operate near the hot section of the engine. Due to the limited number of types of microprocessors available in the extended temperature range grading, it was necessary to fully utilize the limited hardware resources and implement preemptive multitasking. For this purpose, a custom operating system and communication protocol were designed. The protocol hosts the middle layer which hides the implementation of the distributed system. The presented architecture ensures the sufficient computational capacity in individual nodes of the network operated in adverse conditions. It is scalable and resistant to transmission errors.
ARTICLE | doi:10.20944/preprints201802.0028.v1
Subject: Medicine & Pharmacology, Ophthalmology Keywords: glaucoma; ab interno trabeculectomy; goniotome; trabectome; Kahook Dual Blade; MIGS; minimally invasive surgery
Online: 5 February 2018 (03:50:14 CET)
Objective: To evaluate three different microincisional ab interno trabeculectomy procedures in a porcine eye perfusion model. Methods: In perfused porcine anterior segments, 90 degrees of trabecular meshwork (TM) were ablated using the Trabectome (T; n = 8), Goniotome (G; n = 8), or Kahook device (K; n = 8). After 24 hours, additional 90 degrees of TM were removed. Intraocular pressure (IOP) and outflow facility were measured at 5 µL/min and 10 µL/min perfusion to simulate an elevated IOP. Structure and function were assessed with canalograms and histology. Results: At 5 µL/min infusion rate, T resulted in a greater IOP reduction than G or K from baseline (76.12% decrease versus 48.19% and 47.96%, P = 0.013). IOP reduction between G and K was similar (P = 0.420). Removing another 90 degrees of TM caused an additional IOP reduction only in T and G but not in K. Similarly, T resulted in the largest increase in outflow facility at 5 µL/min compared with G and K (first ablation: 3.41 times increase versus 1.95 and 1.87; second ablation: 4.60 versus 2.50 and 1.74) with similar results at 10 µL/min (first ablation: 3.28 versus 2.29 and 1.90 (P = 0.001); second ablation: 4.10 versus 3.01 and 2.01 (P = 0.001)). Canalograms indicated circumferential flow beyond the ablation endpoints. Conclusions: T, G and K significantly increased the outflow facility. In this model, T had a larger effect than G and K.
ARTICLE | doi:10.20944/preprints201901.0139.v1
Subject: Life Sciences, Microbiology Keywords: E. coli O157:H7; non-intact beef; mechanical tenderization; blade tenderization; antimicrobial interventions; translocation
Online: 14 January 2019 (12:15:28 CET)
The USDA-FSIS considers mechanically-tenderized beef as ‘non-intact’ and a food safety concern because of the potential for translocation of surface E. coli O157:H7 into the interior of the meat that may be cooked ‘rare or medium-rare’ and consumed. We evaluated 14 potential spray interventions on E. coli O157:H7-inoculated lean beef wafers (~106 CFU/cm2 , n=80) passing through a spray system (18 sec dwell time, ~40 PSI) integrated into the front end of a Ross TC-700MC tenderizer. Inoculated and processed beef wafers were stomached with D/E neutralizing broth and plated immediately, or were held in refrigerated storage for 1-, 7-, or 14 days prior to microbial plating. Seven antimicrobials that showed better performance in preliminary screening on beef wafers were selected for further testing on beef subprimals in conjunction with blade tenderization. Boneless top sirloin beef subprimals were inoculated at ~2 x 104 CFU/cm2 with a four-strain cocktail of Escherichia coli O157:H7 and passed once, lean side up, through an integrated spray system and blade tenderizer. Core samples obtained from each subprimal were examined for the presence/absence of E. coli O157:H7. Absence of E coli O157:H7 translocated into core samples correlated with the ability of the antimicrobials to reduce bacterial levels on the surface of beef prior to blade tenderization.
ARTICLE | doi:10.20944/preprints202109.0332.v2
Subject: Engineering, Electrical & Electronic Engineering Keywords: Near-net-shaped Blade; Adaptive Machining; Small Object Detection; Neural Network; Transformer; Real-Time Detection
Online: 4 January 2022 (11:12:43 CET)
In the leading/trailing edge’s adaptive machining of the near-net-shaped blade, a small portion of the theoretical part is retained for securing aerodynamic performance by manual work. However, this procedure is time-consuming and depends on the human experience. In this paper, we defined retained theoretical leading/trailing edge as the reconstruction area. To accelerate the reconstruction process, an anchor-free neural network model based on Transformer was proposed, named LETR (Leading/trailing Edge Transformer). LETR extracts image features from an aspect of mixed frequency and channel domain. We also integrated LETR with the newest meta-Acon activation function. We tested our model on the self-made dataset LDEG2021 on a single GPU and got an mAP of 91.9\%, which surpassed our baseline model, Deformable DETR by 1.1\%. Furthermore, we modified LETR’s convolution layer and named the new model after GLETR (Ghost Leading/trailing Edge Transformer) as a lightweight model for real-time detection. It is proved that GLETR has fewer weight parameters and converges faster than LETR with an acceptable decrease in mAP (0.1\%) by test results.
ARTICLE | doi:10.20944/preprints202008.0270.v1
Subject: Engineering, Marine Engineering Keywords: coupled system; tidal turbine; electrical system; blade element momentum theory; actuator line model; computational fluid dynamics
Online: 12 August 2020 (04:46:13 CEST)
Production of electricity using hydro-kinetic tidal turbines has many challenges that must to be overcome to ensure reliable, economic and practical solutions. Energy from flowing water is converted by a system comprising: the turbine rotor blades, a gearbox, an electrical generator, control systems, power electronics, export cables, and a connection to the electricity grid. To date these have often been modelled using simulations of independent systems, lacking bi-directional, real-time, coupling. This approach leads to critical effects being missed. Turbulence in the flow, results in large velocity fluctuations around the blades, causing rapid variation in the shaft torque and generator speed, and consequently in the voltage seen by the power electronics and consequently the export power quality. The resulting poor quality power may be unacceptable to the grid. Conversely, grid frequency and voltage changes can also cause the generator speed to change, resulting in changes to the shaft speed and torque and consequently changes to the lift and drag forces acting on the blades. Clearly, fully integrated, bi-directional, models are needed. Here we present two fully coupled models which use different approaches to model the hydrodynamics of rotor blades. The first model uses Blade Element Momentum Theory (BEMT), resulting in an efficient tool for turbine designers. The second model also uses BEMT combines this with an actuator line model of the blades coupled to an unsteady computational fluid dynamics (CFD) simulation. This simulation, implemented in OpenFOAM, uses an energy balance to compute the shaft speed. Both the BEMT and CFD models are coupled to an Open Modellica model of the electro-mechanical system. Both models have been used to simulate the performance of a 1.2m diameter, scale model, of a three bladed horizontal axis tidal turbine tested in the University of Edinburgh FloWave Ocean Energy Research Facility. The turbulent flow around the blades and the mechanical-electrical variables during the stable period of operation are analysed. Time series and tabulated average values of mechanical thrust, power, torque, and rotational speed as well as electrical variables of generator power, electromagnetic torque, voltage and current are presented for the coupled system simulation. The relationship between the mechanical and electrical variables and the results from both tidal turbine approaches are discussed. Our comparison shows that while the BEMT model provides an effective design tool (leading to slightly more conservative designs), the CFD/BEMT simulations provide more accurate predictions of the blade loads which can be especially important in assessing fatigue on the blades (though at an increased computational cost).
ARTICLE | doi:10.20944/preprints201911.0036.v1
Subject: Engineering, Mechanical Engineering Keywords: turboshaft; axial compressor; blade; FEM; CFD; erosion; wear; stall margin; compressor surge; brownout; gas-turbine performance
Online: 4 November 2019 (03:58:12 CET)
This paper analyses the health and performance of 12-stage axial compressor of the TV3-117VM/VMA turboshaft operated in a desert environment. The results of the dimensional control of 4,800 worn blades are analysed to model the wear process. Operational experience and numerical simulations are used to assess the effectiveness of an Inlet Particle Separator. Numerical modal analysis is performed to generate the Campbell diagram of worn blades and identify resonant blade vibration which can lead to high cycle fatigue (HCF). It is shown that the gradual loss of the stall margin over time determines the serviceability limits of compressor blades. Recommendations setting out go / no-go criteria are made to maintenance and repair organisations.
ARTICLE | doi:10.20944/preprints201905.0049.v1
Subject: Engineering, Mechanical Engineering Keywords: design optimization; axial compressor blade; Sweep angle; Taper; Dihedral angles; Aero elasticity; multidisciplinary design optimization; computational fluid dynamics
Online: 6 May 2019 (10:29:25 CEST)
In this study, an optimization of the first blade in new test rig presented. Blade tuning is conducted using 3D geometrical parameters. Sweep and dihedral play an essential role in this study. Compressor characteristics and blades vibrational behavior are the main objective of the evaluation. Here, the attachments are designed to isolate blade dynamics from Disk. So, the Vibrational behaviors of the one's blade are tuned based on the self-excited and forced vibration phenomenon. Using a semi analytical MATLAB code instability conditions are satisfied. The code takes advantages of whitehead and force response theory to predict classically and stall flutter speeds. Beside, Forced vibrations instability is controlled using a theory presented by Campbell. Aerodynamics of new blade geometry determined using multistage simulations Computational fluid dynamics (CFD) software. Numerical results show increasing performance near the surge line and working interval along with increasing mass flow.
ARTICLE | doi:10.20944/preprints202011.0303.v1
Subject: Engineering, Automotive Engineering Keywords: turbofan; unmanned aerial vehicles; cruise missile; aerial target; axial compressor; blade; titanium alloy; aluminium alloy; titanium aluminide; safety factor
Online: 10 November 2020 (11:20:07 CET)
BACKGROUND: Manufacturing costs, along with operational performance, are among the major factors determining the selection of the propulsion system for unmanned aerial vehicles (UAVs), especially for aerial targets and cruise missiles. OBJECTIVES: In this paper, the design requirements and operating parameters of small turbofan engines for single-use and reusable UAVs are analysed to introduce alternative materials and technologies for manufacturing their compressor blades, such as sintered titanium, a new generation of aluminium and an alloy based on titanium aluminides. METHODS: To assess the influence of severe plastic deformation (SPD) on the hardening efficiency of the proposed materials, the alloys in the coarse-grained and submicrocrystalline states were studied. Changes in physical and mechanical properties of materials were taken into account. The thermodynamic analysis of the compressor was performed in a finite element analysis system (ANSYS) to determine the impact of gas pressure and temperature on the aerodynamic surfaces of compressor blades of all stages. RESULTS: Based on thermal and structural analysis, the stress and temperature maps on compressor blades and vanes were obtained, taking into account the physical and mechanical properties of advanced materials and technologies of their processing. The safety factors of the components were established based on the assessment of their stress-strength reliability. Thanks to nomograms, the possibility of using the new materials and the technologies was confirmed in view of the permissible operating temperature and safety factors of blades. CONCLUSIONS: The proposed alternative materials and production technologies for the compressor blades and vanes meet the design requirements of the turbofan at lower manufacturing costs.
ARTICLE | doi:10.20944/preprints201808.0283.v1
Subject: Engineering, Mechanical Engineering Keywords: wind tunnel; enlarge design; Buckingham π theorem; torque-diameter correlation; estimated power; field size; 3-D blade; stall delay
Online: 16 August 2018 (12:47:10 CEST)
A preliminary study of a wind turbine design is carried out using a wind tunnel to obtain its aerodynamic characteristics. Utilization of data from the study to develop large-scale wind turbines requires further study. This paper aims to discuss the use of wind turbine data obtained from the wind tunnel measurements to estimate the characteristics of wind turbines that have field size. The torque of two small-scale turbines was measured inside the wind tunnel. The first small-scale turbine has a radius of 0.14 m and the second small turbine has a radius of 0.19 m. Torque measurement results from both turbines were analyzed using Buckingham π theorem to obtain a correlation between torsion and diameter variations. The obtained correlation equation is used to estimate the field measurement of turbine power with a radius of 1.2 m. The resulting correlation equation can be used to estimate the power generated by the turbine by the size of the field well in the operating area of the tip speed ratio of the turbine design.