Number Of Rotor Blades Research Articles

Designing and FEM simulation of the helicopter rotor and hub

The paper presents a preliminary design of the three-blade rotor. The geometric model was prepared in the Siemens NX 12.0 programme. After the preparation of the model and kinematic analysis, the structure was checked for strength by means of NX Nastran software. In addition, structural solutions of bearing rotors currently used in the construction of helicopters were discussed and a comparative analysis of the developed rotor design with other rotors was carried out in order to define the basic advantages and disadvantages of each solution. The main rotor of a helicopter is considered the most important component of the rotorcraft, which determines its performance. Rotating blades generate the resultant forces and moments in the rotor hub that allow the helicopter to fly. In the case of a single-rotor helicopter design, a tail rotor must be added to obtain directional control. Cyclic and collective control of blade inclination influences the generation of aerodynamic and inertial loads, which depend on the azimuthal position of the blade on the rotor disc. The number of rotor blades and the properties of the blade-hub connections strongly influence the level of load transfer from the blades through the hub to the helicopter fuselage. By incorporating a set of hinges, it is possible to reduce the component loads of the rotor, tilt and rolling moments transferred to the hull. A conventional articulated rotor head with built-in hinges requires frequent maintenance, which increases helicopter operating costs. Furthermore, a complex structure with a large number of components increases the weight of the articulated rotor.

Study of Noise Reduction Based on Optimal Fan Outer Pressure Ratio and Thermodynamic Performance for Turbofan Engines at Conceptual Design Stage

With the development of civil aero-engines, the noise emission is now an essential issue to be considered during engine design. In this study, the preliminary design for a model fan, which was used for the fan noise estimation, was carried out. The fans with different bypass ratios, different tip speed as well as different aspect ratio were designed and the rough dimensions of the fan were obtained. Based on the dimension and performance of the fan, the effect of fan bypass ratio, tip speed, rotor blade numbers, and rotor–stator spacing on noise generation was investigated. The results indicate that the fan noise can be reduced as high as 10 dB by the increase of bypass ratios, and fewer rotor blade numbers and larger rotor–stator spacing are proved to be benefit to the fan noise reduction as well. However, lower tip speed does not achieve the noise reduction as expected. This is because more rotor blades are added to maintain the constant fan pressure ratio for the fan with lower tip speed. The study demonstrates that trade-off study should be carried out when considering fan noise reduction during engine design.

Hydrostructural Optimization of a Marine Current Turbine Through Multi-fidelity Numerical Models

A marine current turbine (MCT) that extracts energy from ocean currents should be hydrodynamically and structurally stable to generate uninterrupted power. This can be achieved through the shape optimization of MCT blades. In this work, a horizontal axis MCT of 0.8 m diameter was optimized through multi-fidelity numerical approach. The design parameters such as blade pitch angle (θ) and the number of rotor blades (NR) were modified to increase the power coefficient (CP) and to reduce the von-Mises stress (σv) using multi-objective optimization technique. A coupled fluid–structure interaction method is used for fluid and structural analysis of MCT. Also, an analysis for identifying the cavitation inception is incorporated. A surrogate-based optimization code was used to produce a Pareto optimal front. The MCT with CP = 0.451 encountered σv = 125.83 MPa and a high total deformation (TD) = 20.259 mm near the blade tip. The TD of the same MCT blade was later reduced to 1/3rd of its actual value by identifying an alternate turbine material. The losses due to vortices, wake generation, and cavitation study are discussed in the present work.

Computational model of simultaneous wave and sea current loads on tidal turbines

A computational model of simultaneous wave and sea current loads on tidal turbines was developed based on the rotor disc theory. Sea current profile and wave velocity components were defined in a cylindrical coordinate system positioned at the free surface. Tidal turbine loads were evaluated using the Modified Blade Element Momentum Theory by integrating the elemental thrust and torque values along the turbine blades. The analysis was performed in the time domain by considering various waves, hub heights, two and three turbine blades. An envelope of tidal turbine loads, which is the worst case scenario from the structural safety point of view, is presented. It provides forces and moments experienced by the tidal turbine in all three characteristic directions. An analysis of the flow velocity, elemental thrust and torque is provided as well as asymmetries in their respective distributions. The effects of the tidal turbine hub height and the number of rotor blades on the tidal turbine loads were investigated as well. A favorable increase in the power output for a tidal turbine situated closer to the sea surface is accompanied by an adverse substantial increase in tidal turbine loads, which is particularly exhibited for the pitch and yaw moments.

Optimization of a horizontal axis marine current turbine via surrogate models

Flow through a scaled horizontal axis marine current turbine was numerically simulated after validation and the turbine design was optimized. The computational fluid dynamics (CFD) code Ansys-CFX 16.1 for numerical modeling, an in-house blade element momentum (BEM) code for analytical modeling and an in-house surrogate-based optimization (SBO) code were used to find an optimal turbine design. The blade-pitch angle (o) and the number of rotor blades (NR) were taken as design variables. A single objective optimization approach was utilized in the present work. The defined objective function was the turbine\'s power coefficient (Cp). A 3x3 full-factorial sampling technique was used to define the sample space. This sampling technique gave different turbine designs, which were further evaluated for the objective function by solving the Reynolds-Averaged Navier–Stokes equations (RANS). Finally, the SBO technique with search algorithm produced an optimal design. It is found that the optimal design has improved the objective function by 26.5%. This article presents the solution approach, analysis of the turbine flow field and the predictability of various surrogate based techniques.

Numerical Studies of BPF Pressure Pulsation in Centrifugal Ventilators

There is a link between pressure pulsations in the centrifugal ventilator working cavity and its noise level on blade passing frequencies (BPF). They result from non-stationary hydrodynamic interaction between the impeller flow and volute casing. Pressure pulsations depend on quality of hydraulic profiling of ventilator. The amplification of pressure pulsations can happen due to matching of frequencies of oscillations with acoustic resonance frequencies. In ventilators the length of acoustic waves can be comparable to the size of the casing. Therefore, the variation of rotation speed, number of rotor blades, the fan installation in the ventilation system can substantially modify amplitudes of pressure pulsations due to the resonance inside the ventilator cavity. Various numerical studies of BPF pressure pulsation in ventilators are undertaken using the method and software package based on a representation of non-stationary motion of a compressible medium as a superposition of acoustic and vortex modes. In this case non-linear equations for unsteady vortex motion of an incompressible liquid are solved with a bigger time step. Wave equation relative to the pressure pulsations considering acoustic impedances on the borders of computational domain is solved by an explicit method. As a result, the whole processor time for both modes of oscillations is reduced and accuracy of prediction for the acoustical mode is improved.

Linear Analysis of Vibration Reduction Using an Active Helicopter Rotor

In the field of active rotor control, the use of individual blade control (IBC) systems for vibration reduction is a major topic of research. However, as most studies are focused on a specific helicopter rotor, the influence of topological rotor parameters, such as the number of rotor blades, is seldom investigated. The present investigation analyzes vibration reduction using an IBC system in a very general manner with particular focus on the influence of the number of rotor blades. To this end, a model for the quasi-steady transfer behavior of an IBC rotor with an arbitrary number of rotor blades is derived as a function of the blade transfer behavior using only a minimal set of assumptions. Using this model, a minimal set of blade-root load components relevant for the rotor hub loads is determined. Based on this set of components, a coordinate frame of effective blade-root loads is introduced. Subsequently, the vibration reduction potential for the -bladed rotor is assessed, showing no direct relation between the number of rotor blades and the vibration reduction potential. Finally, the assumptions for the model, as well as the results of the investigation of the vibration reduction potential, are validated using open-loop flight data.

High efficiency design of an impulse turbine used in oscillating water column to harvest wave energy

Abstract Wave energy harvesting systems mostly have low power production capability because of unoptimized design of the system components. A bidirectional flow impulse-turbine used in such a system has efficiency less than 40%, and it is required to design the turbine for a higher efficiency. Present work finds an optimal design and shows design-variable sensitivity to the turbine efficiency. The problem is solved using numerical analysis technique. The flow through the turbine was analyzed by solving the Reynolds-averaged Navier-Stokes equations (RANSE). The design variables; namely number of rotor blades and number of guide vane, guide vane angle and guide vane profile were modified to maximize the turbine efficiency. Using the Latin hypercube sampling technique, sample points were selected from a design space defined by lower and upper limits of the variables. Then, several surrogates were constructed using the RANSE calculated results, and the turbine performance was optimized. The results show that guide vane angle is the most sensitive parameter, while the guide vane profile has negligible effect on efficiency. A hybrid genetic algorithm searched the optimal design point. The relative mean efficiency enhancement over a wide range of flow coefficient was approximately 24%, while it was 28% at maximum efficiency point.

A study on flow fields and performance of water wheel turbine using experimental and numerical analyses

In this paper, an analysis of the performance and flow fields of water wheel turbines for tidal energy extraction is carried out using experimental and numerical methods. The purpose of this work is to develop a water turbine suitable for sites, where fast and shallow surface flows are available, such as rivers or tidal currents. For both methods, the water wheel turbine is tested over a range of tip speed ratios with a differing number of rotor blades, ranging between three and twelve. The results indicate that the numerical simulation shows agreement with the experiment in most cases. Also, the water wheel turbine operates effectively at a range of small tip-speed ratios, where the highest turbine efficiency is produced. Under the same working conditions, the turbines using between six and nine blades generate a greater efficiency and cause lesser reverse flows than others when submerged in water. In contrast, the 3-bladed turbine is the least efficient design as it produces the lowest amount of energy and causes intense vibrations and noises. These noises are a result of a collision between the incoming flow of the channel and the wheel blades during the experimentation, especially at high load conditions. By adding more blades, the torque generated is improved considerably; however, the upstream and downstream depths of the turbine, in this case, are also elevated significantly. Furthermore, in the inlet region, the 3-bladed and 6-bladed turbines have a smaller shock loss and a lower resistance to the main flow from the inlet than the others. Meanwhile, it is found that the flow in the outlet region on the turbines with between nine and twelve blades is in the opposite direction to the wheel’s rotation, significantly obstructing the main flow from the inlet.

The influence of the number of rotor blades on the performance of orthopter wind turbine

This paper describes the influence of the number of rotor blades the performance of the orthopter wind turbine. The orthopter wind turbine is combination between a drag-type and a lift-type vertical axis wind turbine which each blade combines a rotating movement around its own axis and a rotating movement around turbine's axis. In this case, the pitch of the blades was controlled by using a chain and sprockets arrangement to ensure that the blades rotated around their own axis by 360 degrees during the each two full revolution of the main rotor. To improve the performance of this wind turbine, the number of blades, was investigated by wind tunnel. By conducting two-dimensional unsteady CFD simulations, the power and torque of the vertical axis wind turbine and the flow around blades were also analyzed. The numerical simulation by using turbulence model predicted good agreement of the performance with experiment qualitatively.

Blades Forced Vibration Under Aero-Elastic Excitation Modeled by Van der Pol

This paper employs a new analytical approach to model the influence of aerodynamic excitation on the dynamics of a bladed cascade at the flutter state. The flutter is an aero-elastic phenomenon that is linked to the interaction of the flow and the traveling deformation wave in the cascade when only the damping of the cascade changes. As a case study the dynamic properties of the five-blade-bunch excited by the running harmonic external forces and aerodynamic self-excited forces are investigated. This blade-bunch is linked in the shroud by means of the viscous-elastic damping elements. The external running excitation depends on the ratio of stator and rotor blade numbers and corresponds to the real type of excitation in the steam turbine. The aerodynamic self-excited forces are modeled by two types of Van der Pol nonlinear models. The influence of the interaction of both types of self-excitation with the external running excitation is investigated on the response curves.

Automation of Design Tool for an Axial Flow Gas Turbine Stage Used in Small Gas Turbine Engine

Abstract: This paper describes the automation of 3D design and aerothermodynamic analysis of a high pressure, single-stage axial flow turbine driving the compressor of the small gas turbine engine Jet Cat p200 using an analytical method. The specifications of design are based on the reverse engineering of the small gas turbine. Baseline design parameters such as flow coefficient, stage loading coefficient are close to 0.5 and 1.16 respectively with maximum flow expansion in the NGV rows. In the thermal cycle and 1D analysis calculations, the total conditions of all engine stations and all design controlling parameters are determined. In 2D design analysis, the mean line approach is used to generate the turbine flow path and 2D airfoil design, and by using the free vortex law of blading, five blade sections are generated. These sections are at hub, mean and tip and two intermediate sections between hub-mean and mean-tip using an approximate method to the Ainley, Mathieson, Dunham and Came loss model to meet the design constraints. An average exit swirl angle of less than 5 degrees is achieved leading to minimum losses in the stage. Also, NGV and rotor blade numbers are chosen based on the original turbine object. Blade profile is redesigned using the results from blade-to-blade analysis and through-flow analysis using special analytical method, [1]. Aerothermodynamic parameters like pressure ratios, aerothermodynamic power, and efficiencies are computed analytically. The results are compared with the published data in the engine manual.

Multi‐aspect micro‐Doppler signatures for attitude‐independent L / N quotient estimation and its application to helicopter classification

Micro-Doppler signals returned from the main rotor of a helicopter can be used for feature extraction and helicopter classification. An intrinsic feature of a helicopter that may be extracted from the micro-Doppler signatures is the L/N quotient, where N denotes the number of rotor blades and L is the blade length. However, in monostatic radar, the L/N quotient cannot be accurately estimated due to the unknown attitude angles of non-cooperative helicopters. To solve this problem, an attitude-independent L/N quotient estimation method based on multi-aspect micro-Doppler signatures is proposed in this study. The helicopter is observed from different aspect angles, and the multi-aspect micro-Doppler signatures are jointly processed to solve the attitude angles of the helicopter and estimate the L/N quotient unambiguously. Experiments with both simulated and real data demonstrate that, the proposed method is robust with respect to the attitude of the helicopter and, therefore, significantly improves the accuracy of L/N quotient estimation compared with only using the signature observed from single-aspect angle. This implies that the proposed method has the potential to increase the success rate of helicopter classification.

Strength and gas dynamic methods of development of the axial turbine turbocharger

The results of strength and gas dynamic improvement of the turbocharger TK-32 axial turbine are presented. The turbocharger is manufactured by LLC “Penzadieselmash” (Penza, Russian) and is used as unit boost for a diesel locomotive. The aim of this work was to ensure the turbine work capacity when the rotor speed is increased by 10% without efficiency reduction. The strain-stress state analysis indicated the region of high stresses on the rotor blade body at the level of 2/3 of root. These stresses exceed allowable values when the rotor speed increased. The variant of tangential displacement of the peripheral rotor blade section, allowing reducing the level of stress by 20%, was found. Gas dynamic calculation showed that the variant of rotor blade modernization results in an increase of efficiency by 0.4%. Also it was shown that the increase in turbine efficiency by 1% can be reached if the number of rotor blades is reduced by 13%. This recommendation was implemented and confirmed experimentally by the example of mass turbocharger TK-32 [1].

Unsteady Flow Evolution Through a Turning Midturbine Frame Part 2: Spectral Analysis

This paper analyzes the propagation of the aerodynamic deterministic stresses through a two-spool counter-rotating transonic turbine at Graz University of Technology. The test setup consists of a high-pressure stage, a diffusing midturbine frame with turning struts and a counter-rotating low-pressure rotor. The discussion of the data is carried out in this second part paper on the basis of spectral analysis. The theoretical framework for a double Fourier decomposition, in time and space, is introduced and discussed. The aim of the paper is the identification of the sources of deterministic stresses that propagate through the turbine. A fast-response aerodynamic pressure probe has been employed to provide time-resolved data downstream of the high-pressure rotor and of the turning strut. The fast-response aerodynamic pressure probe measurements were acquired together with a reference signal (a laser vibrometer) downstream of the high-pressure rotor to identify different sources of deterministic fluctuations. The discussion is completed by fast-response pressure measurements on the strut surface and computational fluid dynamics computation to detail which deterministic stress related to the high-pressure stage propagates through the duct. The double Fourier decomposition shows that structures at the periodicity of the rotor blade number decay, whereas the unsteadiness at the outlet of the duct is the result of vane–rotor–vane interaction.

Helicopter vs. volcanic tremor: Characteristic features of seismic harmonic tremor on volcanoes

We recorded high-frequency (>10Hz) harmonic tremor with spectral gliding at Hekla Volcano in Iceland. Particle motion plots indicated a shallow tremor source. We observed up to two overtones beneath our Nyquist frequency of 50Hz and could resolve a source of closely spaced pulses of very short duration (0.03-0.1s) on zoomed seismograms. Volcanic tremor with fundamental frequencies above 5Hz, frequency gliding and/or repetitive sources similar to our observations were observed on different volcanoes around the world. However, this frequency content, duration and occurrence of volcano-related tremor was not observed in the last 35years of seismic observations at Hekla. Detailed analysis reveals that this tremor was related to helicopters passing the volcano. This study relates the GPS track of a helicopter with seismic recordings of the helicopter at various distances. We show the effect the distance, number of rotor blades and velocity of the helicopter has on the observed up and down glidings at up to 40km distance. We highlight similarities and differences between volcano-related and helicopter tremor in order to help avoid misinterpretations.

Acoustic Kinematics of Helicopter BVI Noise

Helicopter blade-vortex interaction (BVI) noise is known as a critical source of noise annoyance from helicopters. A key feature of the noise is that the trace velocities of the sources generated by the BVI process are supersonic, and thus have high radiation efficiency. This further means that noise is generated selectively by only a limited part of the overall interaction. The consequences of this have been studied using a simple cycloidal shed wake model. This allows the whole process to be explicitly described mathematically. The trace velocity can be infinite for both forward and retreating blades. This will generate strong noise radiation in directions which can be simply defined as a function of advance ratio. Analysis shows that many features are functions of rotor disc position only, independent of the number of rotor blades. This offers a helpful simplification. Radiation generates a series of caustics which can be defined by the analysis. Simplified models of the blade-wake interaction show that both the advancing and retreating blade interactions can generate cusps in the noise. Under some conditions these cusps are predicted to continue to the far field in the rotor disc plane, due to a kinematic balance of the change in propagation direction of the basic source vector and the change in the Mach angle of the principal radiation. This gives a two-dimensional decay in sound levels and will give rise to locally intense BVI field. The model also shows areas of the stronger noise fields will be generated in the direction of motion of the interacting blade. A detailed analysis has been undertaken for a four blade rotor at an advance ratio of 0.2. Multiple caustics from successive blade interactions can be identified, some of which have cusps. The analysis shows that the BVI radiation field can have large levels locally and helps to explain why helicopters are often perceived to be noisier than a simple dBA level might suggest. Each part of the rotor disc noise radiation to the far field can be related back to specific positions on the blade and specific parts of the shed wake. This offers the prospect of providing local adjustments to minimize BVI sources under particular conditions. All these results are based on the two dimensional cycloidal model. However it is believed that these effects must be reflected in more complex computer models and in real helicopters.

Mean-line modeling and CFD analysis of a miniature radial turbine for distributed power generation systems

Distributed power generation (DPG) based on organic Rankine cycle offers potential in the effective use of energy from low grade heat sources up to 2008C. In this regard, developing an effective expander plays a major role in determining the overall cycle efficiency. In this work mean-line modeling and CFD techniques are employed to develop a small-scale radial turbine for DPG systems with a power output of 5 kWe. A parametric study is carried out using the mean-line approach to investigate the effects of key input parameters such as operating conditions, velocity ratio, rotational speed and rotor flow angles on the turbine rotor inlet diameter and overall performance. Results from the mean-line approach show that in order to achieve high power output, inlet total temperature, mass flow rate and pressure ratio should be increased. However, for reducing the rotor inlet diameter the velocity ratio should be decreased. CFD technique is then used to assess the flow field and to improve the blade loading by modification of blade angle distribution. CFD is also used to determine the minimum number of rotor blades and the results show that the value suggested by mean-line modeling overestimates this parameter. By using these two approaches a wide range of design configurations are explored and the most effective design is identified to be with specific diameter of 4.83 (rotor inlet diameter of 0.0787 m), specific speed of 0.433 (rotational speed of 55 000 rpm), 10 blades and output power of 4.662 kW.

Design and Performance of a Quad-Shrouded Rotor Micro Air Vehicle

This paper describes the experimental investigation of a quad-shrouded rotor micro air vehicle and focuses on the hover performance improvements over a conventional unshrouded micro quad rotor. The effects of number of rotor blades, blade root pitch angle, and shroud diffuser length on aerodynamic performance were studied. The rotor diameter was 6.6 cm, it had a tip of 20,000, and the gross weight of the vehicle was 90 g, with a shroud weight fraction of 13%. With the optimized design, the power loading of the quad-shrouded rotor was about 15% greater than the unshrouded configuration. To completely evaluate the configuration, the performance of the vehicle in edgewise flow was investigated. The drag and pitching moment for the shrouded rotor was about 2.5 times greater than the unshrouded vehicle. However, control-moment measurements suggested that the edgewise gust tolerance was at least . The vehicle prototype was also successfully flight tested in hover using onboard feedback regulation. Based on these studies, the shrouded rotor concept appears feasible in improving performance of a conventional micro quad rotor even at and can be easily retrofitted into existing configurations.

Forced Response in Axial Turbines Under the Influence of Partial Admission

High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%–105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.