Helicopter Main Rotor Research Articles

Numerical Study of Fuselage Impact on Acoustic Characteristics of a Helicopter Rotor

The paper presents the results of the simulation of unsteady turbulent flow generated by helicopter main rotor in the presence of the fuselage with an emphasis on the analysis of the influence of the fuselage on the rotor-induced flow and the rotor-generated acoustic field. The Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model are used to simulate the Caradonna–Tung rotor and ROBIN fuselage interaction in hovering flight. The governing equations are discretized using the vertex-centered control volume method on mixedelement unstructured meshes with the sliding mesh technology to treat the rotor. The acoustic field generated by the rotor+fuselage interaction is comparatively analyzed against the case of an isolated rotor. It is found that the presence of fuselage significantly changes the rotor-generated acoustics. In particular, the presence of the fuselage noticeably distorts the directivity of acoustic radiation and increases the overall sound pressure level under the fuselage up to 20 dB, emphasizing the importance of the influence of fuselage on the helicopter acoustics.

To the problem of simulation modelling of abnormal and emergency flight situations in the process of Mi-8MTV helicopter pilot simulation training

The article examines a method of obtaining the required initial data for adequate mathematical modelling of nonstationary processes in the Mi-8MTV helicopter computer and flight simulators. The principle of the method is as follows: the video fixation of non-stationary modes of the power plant operation in a real flight and the computation of the obtained dependencies according to the known formulas of mechanics, aerodynamics, the theory of gas turbine aircraft engines, etc. are analysed. Moreover, by juxtaposing the computed dependencies and the obtained video fixation, the parameter values, that determine the helicopter power plant behaviour (the inertia moment of the helicopter main rotor system, etc.) in the non-stationary modes, are found. These parameters allow us to solve the problem by modelling a complete picture of the helicopter power plant behaviour in abnormal and emergency situations, under which, it is impossible to formulate an objective verdict without violating flight safety requirements. Given the circumstances, the feasibility of an advantageous and reliable solution to the problem is considered using mathematical modelling of the transient power plant operation modes both in non-stationary conditions and in abnormal and emergency situations. A simulation of these scenarios and responsive actions is carried out using helicopter simulators. In a real flight, a helicopter crew monitors the functional systems status and the development of abnormal and emergency situations relying on readings from dial instruments, digital indicators, annunciators, and other computer-aided facilities in the cockpit, not only by the parameter values, but also by dynamics of their variation in flight. Within this timespan, the pilot must assess an abnormal situation and decide on required actions.

Comparative Analysis of the Vibrational Response of a Homemade Helicopter Main Rotor Blade Profiles

This paper investigates the dynamics of homemade helicopter wooden and aluminum sheet rotor blades. The rotors are articulated and their blades are rigid. The main rotor implementation takes into account flap, lag, and feather degrees of freedom for each of the equispaced blades as well as their dynamic couplings. Transmitted vibrations due to the rotating rotor blades on the body structure (fuselage) are studied. This work presents an aerodynamic model of main rotor blades that allows us to analyse vibrational transmissions on the fuselage (body) of the craft. Vibrations in helicopters is a common problem which involves complex interactions between the inertial, structural and aerodynamic loads, especially in homemade helicopters. The major source of vibrations in helicopters is the main rotor. The efficiency and stability of the main rotor blades is determined by the magnitudes of the predominant frequencies they produce. These vibrations affect the functionality, durability of the engine component parts, increase maintenance frequency (cost), and cause structural failures. The aerodynamic model has been built up using blade element theory. The aerodynamic load creates vibrations on the homemade helicopter and these are analyzed on the fuselage by using a short time Fourier transform that brings out the vibrational spectrum. The results of the analysis serve as a reference to characterize the stability and efficiency of homemade main rotor blade profiles.

Selection of the Optimal Airfoil for the Small-Sized Unmanned Helicopter Main Rotor Blade

Selection of the Optimal Airfoil for the Small-Sized Unmanned Helicopter Main Rotor Blade

Helicopter Main Rotor Blade Parametric Design for a Preliminary Aerodynamic Analysis Supported by CFD or Panel Method.

This work is the preliminary part of a research program which is aimed at finding some new methods and design solutions for helicopter main rotor multidisciplinary optimization. The task was to develop a parametric geometric model of a single-blade main rotor applicable for varied methods of numerical aerodynamic modeling. The general analytical assumptions for the parametric main rotor design were described. The description of the main rotor blade parametric design method based on Open GRIP graphical programming was presented. Then, the parametric model of a blade was used for aerodynamic models independently developed for panel method and advanced CFD solver. The results obtained from the CFD simulations and panel analysis for main rotor aerodynamics were compared and assessed using analytical calculations. The calculations and simulations for a single-blade and completed rotor were performed for different helicopter weights and rotor pitch angles. The results of different computer aerodynamic analysis environments were compared for the possibility of their application in an optimization loop. This is preliminary work that describes only a partial problem that could be used in the future as part of a comprehensive methodology for aerodynamic and structural optimization of a helicopter rotor. As an output of the research, new options for main rotor optimization are developed. The combined parametric modeling with aerodynamic analysis, as described in this paper, provide the preliminary design for a main rotor spiral, as an element of the optimization loop.

Technological Aspects of a Reparation of the Leading Edge of Helicopter Main Rotor Blades in Field Conditions

The Polish Air Force operates more than one hundred helicopters of the Mi family (manufactured by Mil Helicopters), equipped with metal main rotor blades. The main rotor blades are among the most stressed components of these structures. For this reason, they are subject to more frequent inspections during operation than other components. One type of damage detected during inspections is the local disbonding of fragments of the anti-erosion layer from the leading edge. This harmless-looking damage is very dangerous, since it quickly leads to the complete detachment of the layer. The leading edge, unprotected by the metal cover, erodes rapidly. The detached layer, when thrown away at high speed, endangers other parts of the helicopter, such as the tail rotor, and may cause damage to other helicopters if flying in formation. The technology supplied by the manufacturer to date has not encompassed the field repair of this type of damage. Therefore, efforts were made to develop repair technology for rapid repairs of blades in field conditions during missions of the Task Force White Eagle in Afghanistan. This article presents the concept of repair technology feasible in field conditions and presents the results of post-repair edge tests. Test results to identify the materials used in the construction of the trailing edge are also presented. The results of materials testing facilitated the development of technological processes, and, in the future, will aid the selection of a substitute bonding paste system with similar parameters that are essential for repairs.

Aerodynamic noise separation of helicopter main and tail rotors using a cascade filter with Vold-Kalman filter and cyclic Wiener filter

The noise issue has become an important factor limiting the massive application of helicopters as the requirements for helicopter reliability and comfort continue to increase. As the primary noise source of helicopters, the main and tail rotor aerodynamic noise should be separated for individual noise reduction investigations. According to the frequency domain characteristics, the rotor aerodynamic noise can be divided into tonal noise and broadband noise. A cascade filtering method with Vold-Kalman filter and cyclic Wiener filter is proposed in this paper to separate the tonal and modulated broadband noise of the main and tail rotors, respectively. The classical method only considers the periodic characteristics of the main and tail rotor aerodynamic noise for harmonic separation. The broadband noise is not considered within the separation of interest due to its randomness, which leads to the inaccuracy of the conventional method for the aerodynamic noise separation of the main and tail rotors. The broadband noise exhibits a second-order cyclostationarity due to the periodic modulation of the rotational motion of the rotor. According to its cyclostationarity, while considering the periodicity of tonal noise for harmonic separation, the proposed cascade filtering method also performs the separation of broadband noise. More precise separations of the main and tail rotor can be obtained by this method. The efficacy of the proposed cascade filtering method is demonstrated in both the simulation and wind tunnel noise measurement.

An assessment of the transient effect on helicopter main rotor stability and power demand

The researched object os a helicopter main rotor with blades of variable geometric twist characteristics. Variable torsion refers to systems of actuators made of shape memory alloys. The presented numerical analyses allow for evaluating both the dynamics of the rotor in transient states, i.e. in the zone between the static phase and the full activation phase and the impact of the change on the pulsation of the amplitude of the necessary power generated by the rotor corresponding the flight state, and thus covering the demand by the disposable power generated by the engine. This study follows a methodology of numerical analyses based on Multi Body Dynamics and the Finite Element Method and uses fluid mechanics elements and algorithms to analyze lift generation, compiled in a single computational environment referring to the same period of time.

A Review on Vibration Analysis of Helicopter Rotor Blade

Abstract: Vibration has always been a major disturbance for helicopter. Vibrations, thus, a threat to components of helicopter. The vibration created by a helicopter draws a great contribution to the reduction in life of the components. Reducing the vibration that creates from helicopter rotor blades, tail rotors is a one step closer to this crisis. Helicopter Vibration control is a topic of research into designing helicopter rotor blade which can be operated more efficiently. The major source of the vibration come from the rotor blade rotation. By trying to upgrade new design in the helicopter main rotor blades and tail rotors reduce the vibration and make the operation more efficient. This paper addresses simulation and analysis of vibration level of rotor blades. Keywords: drag, rotor, vibration, air foil, blade profile.

МЕТОД ВИЗНАЧЕННЯ ХАРАКТЕРИСТИК НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ЛОНЖЕРОНА РЕГУЛЯРНОЇ ЧАСТИНИ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА ДОПОМОГОЮ СИСТЕМИ ANSYS

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. To determine the fatigue life of the blade it is necessary to know the characteristics of the stress-strain state. A method has been developed for determining the characteristics of the stress-strain state of the spar of the regular part of the rotor blade of a helicopter using the ANSYS system. Application of numerical methods of stress-strain state characteristics calculation allows to reduce considerably time and cost of blade design. The calculation results of regular part of the Mi-8 main rotor blade at the hover mode when it is loaded by aerodynamic and inertial load from the rotation, as well as the force of its own weight are presented in the work. Using the ANSYS system, a finite-element model of the regular part of the blade, consisting of a set of beam elements of variable cross-section, was developed, the calculation was carried out taking into account the geometric nonlinearity of the structure behavior and the analysis of the obtained results. To describe the response of materials to external influences, an elastically deformable isotropic body model is used with assignment of the appropriate elastic constants of the material. Analysis of calculation results includes determination of reactions at attachment points, values of maximum displacements of structural elements and stresses in weak sections. Diagrams of internal force factors (axial and shear forces and bending moment) along the blade span are plotted. With the help of these diagrams weak sections are determined and values of axial force and bending moment in these sections are calculated. Axial force reaches its maximum value Nx = 333689 N in the section along the axis of rib № 1. In this section, the bending moment reaches a maximum value of Mymax = 3078.3 N×m. At cross section r = 0.73 between axes of ribs No. 13 and No. 14, where shear force equals to zero, value of bending moment My = -1147,5 N×m. Thus, regular part of the blade is in combined stressed state - bending with tension. Static strength of the blade has been estimated using safety factor. To estimate a static strength equivalent von Mises stresses were considered as the maximum stresses. Safety factor of static strength of regular part of the blade in the weak section was 1,7. To estimate fatigue strength, distribution of the first principal stresses in the load-carrying elements was analyzed in terms of typical stress concentrators. The maximum level of the principal stresses in the considered sections was s1 = 138 MPa, which indicates that the blade material operates in the range of high cycle fatigue.

Aerodynamic performance analysis of a supercritical airfoil in the helicopter main rotor

Helicopters can be considered as any-terrain vehicles, as they can take off and land at any location. The aerodynamic characteristics of helicopters are more complicated than those of fixed-wing aircraft. The rotor is the source of lift and thrust for helicopters. The complex aerodynamic characteristics of helicopters are due to their rotational frame and variations in the velocity and pressure throughout the blades. Moreover, the airfoil undergoes phase changes because half of the phase exhibits a trailing edge toward the flow. In this study, four isolated helicopter rotor blades were analyzed using ANSYS Fluent in terms of flow in a static domain under non-rotating conditions. Supercritical airfoils used in high-speed aircraft have been found to be incredibly useful in the transonic region. They increased the critical and drag divergence Mach numbers. Incorporating supercritical airfoils in helicopter rotor blades ensures suitable flow characteristics and more than 50% efficiency compared to those of the HH02 blade in a stationary frame. Analyses were conducted for HH02 and NASA SC(2)-0714 airfoils with Mach numbers of 0.3, 0.4, and 0.5 without rotation. The post-processing results prove that the NASA SC(2)-0714 airfoil rotor achieves a better aerodynamic performance than the HH02 airfoil rotor.

Forward Flight Performance Analysis of Supercritical Airfoil in Helicopter Main Rotor

In this research, the aerodynamic performance and flow characteristics of NASA SC (2)-0714 airfoil and HH02 airfoil in the helicopter main rotor are evidently analyzed. The supercritical airfoil is used in the aircraft for attaining better transonic and high-speed flow characteristics. Moreover, a specialized helicopter airfoil called HH02 is used in the Apache helicopter rotor for increasing the operational speed. As most of the high-speed helicopters are using four-bladed main rotor configuration, it is analyzed with prior attention. The lift and thrust act in different directions for the forward phase of the flight whereas the lift and thrust act in the same direction for the other phases of flight, which is analyzed in this work. The computational analysis is done by using ANSYS Fluent whereas the rotational analysis is done by using the Multiple Reference Frame (MRF) method. An analysis is carried out for different RPM of 400,600 and 800 with the combination of 0.3, 0.4 and 0.5 Mach numbers with the assistance of grid independence test. The result shows that the NASA SC (2)-0714 rotor increases the thrust of the rotor around 5% to 10% under various rotor and forward speeds. Thus, the results proves that the supercritical airfoil is highly capable of producing higher thrust and good aerodynamic characteristics.

Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.

Main rotor blade modeling approaches comparison. Finite element and Craig-Bampton methods

The paper focuses on the helicopter main rotor blade FE model. And the main goal is to prove the feasibility of the helicopter main rotor MBD model in calculations of blade deformation as a result of applied aerodynamic forces. FE model is used as a basis for two different computational methods. A mathematical approach in the MBD based on the Craig-Bampton method on the one hand. And finite element model on the other hand. The results of high-frequency blade rotations are obtained. Calculations of these models are compared in order to determine the best method for modeling a linear-elastic blade. By the results, it is necessary to consider the preloaded state of the blade when using the Craig-Bampton method approach. The comparison of blade nodes displacements at various external conditions for both models are given. The influence of rotor MBS model damping parameters on the amplitude of blade oscillations under sinusoidal action is considered.

АНАЛІЗ КОНСТРУКТИВНО-ТЕХНОЛОГІЧНИХ ОСОБЛИВОСТЕЙ ЛОПАТЕЙ НЕСУЧИХ ГВИНТІВ ВАЖКИХ ТРАНСПОРТНИХ ВЕРТОЛЬОТІВ

The analysis of the design and technological features of the rotor blades of heavy transport helicopters is carried out. The main performance characteristics of heavy helicopters are presented. General requirements to helicopter main rotor blades design and specifications for their production are formulated. The design and force diagram of heavy helicopter main rotor blades is considered. The features of structural materials for the main rotor blades of heavy transport helicopters are marked. The main rotor blades differ in their design due to different approaches to materials, manufacturing and layout of blade elements. The main rotor blades of an all-metal design, for design and technological reasons, are divided into two groups: a frame structure with a tubular steel spar and an aluminum extruded spar. As a result of a number of design and technological measures the service life of the main rotor blade of helicopter Mi-6 was brought from 50 hours to 1500 hours. The principal peculiarity of the steel tubular spar of the main rotor blade of the Mi-26 helicopter is the absence of the shaft lug. The features of mixed design main rotor blades are presented. The method of parametric modeling of helicopter main rotor blades is presented. The application of the three-dimensional parametric models of structural elements in practice of designing and construction enables to perform numerical calculations of aerodynamic and strength characteristics both of separate aggregates, units and details and of the helicopter as a whole by means of the finite element method. The method of parametric modeling of the main rotor blade of the transport helicopter with the computer system CATIA V5 is a modification of the method of integrated designing of the elements of aviation constructions. Parametric master geometry of the main rotor blade is a linear surface, created by basic profiles of the blade. On the basis of parametric master geometry a space distribution model is created that determines the position of axial planes of the power set of the blade for further creation of the blade detail models. Technological flowchart of main rotor blade manufacturing is presented, manufacturing and surface hardening technology of steel tubular spar is considered. The technology of manufacturing and molding the nose part of the blade of the main rotor mixed design. The technological features of slipway assembly-gluing of the main rotor blade are considered, the content of off-slipway work is given.These materials can be useful in theoretical and experimental studies to extend the service life of the rotor blades of Mi-26 helicopters, which are currently in operation in Ukraine.

Numerical Study of the Main Rotor Wake Structures and Induced Velocity Fields at the Tail Rotor Location When Flying Near the Ground

This paper considers the Mi-8 helicopter main rotor aerodynamics when flying near the infinite ground surface. The research is based on the free wake model developed by authors at Moscow Aviation Institute. The distance from the rotor's hub to the ground surface in the range of H = 6-16 m and the values of free stream (flight) velocity in the range of V = 0-15 m/s are considered. The results of the visualization for both rotor wake shapes and streamlines are obtained. The influence of the ground proximity on the rotor wake shape, including the formation of "supervortex" and "ground vortex" structures are analyzed. The induced velocity fields of the main rotor in the area of the tail rotor location for various azimuth positions relative to the main rotor axis are studied. The conclusion is made about the significant influence of the ground effect on the rotor wake structure and induced velocities field, including the area of the tail rotor location. Particularly, at slip flight with speed V = 10 m/s, when the distance to the ground surface H increases from 6 to 12 m, the value of the average induced velocity at the tail rotor plane is growing up to four times. The obtained data have allowed taking into account such effects of aerodynamic interference in the simplified mathematical model of the research flight simulator of JSC Helicopters Mil and Kamov.

Validation and insight of a full-scale S-76 helicopter rotor using the Lattice-Boltzmann Method

This paper describes scale-resolving unsteady flow simulations performed using a Lattice-Boltzmann based solver, applied, for the first time, to a full-scale helicopter main rotor in forward flight. The simulation setup is obtained through a fully automated in-house developed workflow. Validation is performed by comparing thrust and power coefficients with reference wind tunnel data; with and without trimming based on an in-house developed Newton-Raphson trim algorithm. Results for different rotor advance ratios yield insight in both aerodynamic and acoustic quantities for the rotor, highlighting both mean as well as unsteady behavior. Finally, digital helicopter noise certification is performed by calculating the ground noise map for a helicopter in landing condition.

Studying the Possibility of Creating a Dynamically and Elastically Scaled Blade of a Helicopter Main Rotor Model

Studying the Possibility of Creating a Dynamically and Elastically Scaled Blade of a Helicopter Main Rotor Model

Design, analysis and fabrication of a fully articulated helicopter main rotor system

This study describes an integrated framework in which the basic elements of Aerospace Engineering (performance, aerodynamics and structure) and functional elements (suspension, visibility and production) are integrated and considered. In this study, a fully functional rotor system has been fabricated that can be used as one of the training resources for Aeronautical students. For making the rotor system, various parts of the system have been designed on Solidworks and complete mechanism has been simulated with ANSYS. System analysis has been done at various RPM's and Angles of Attack (AOA). In terms of merit the right items have been selected and processed to provide them with the right shape. In terms of the design and implementation, various machines such as gas welding, arc welding, CNC milling and radial machinery have been used. Certain parts such as electric motors, linear actuators and loading cells have been used. All the fabricated components and electric motor, actuator, load cells are then assembled. This rotor system can produce less lift due to high dead weight and low power motor and having some safety issues.

Numerical investigation on noise reduction of rotor blade-vortex interaction using blade surface jet blowing

The effects of blade surface jet blowing on the reduction of rotor blade-vortex interaction (BVI) noise are investigated using the compressible Reynolds-averaged Navier-Stokes equations and the Ffowcs Williams-Hawkings equations. A detailed analysis of the accuracy of the Weighted Essentially Non-Oscillatory (WENO) scheme and Monotone Upstream-Centered Scheme for Conservation Laws for simulating the flow field and predicting the BVI noise is performed using a two-bladed scaled AH-1 helicopter main rotor undergoing BVI as the baseline case. Additionally, a grid convergence study is conducted. The BVI noise is accurately predicted using the fifth-order WENO scheme and high-resolution grid system (the prediction errors of the peak sound pressure are less than 4%). Surface boundary conditions are introduced to model the effect of jet blowing on the blade surface on the flow control of the baseline case. Blade surface blowing is analyzed near the trailing edge and the leading edge near the rotor tip. The results show that blowing near the blade trailing edge is effective for BVI mitigation by altering the tip vortex strength and increasing the blade-vortex miss distance. The sound pressure level is reduced by 2.6 dB, and the peak amplitude is attenuated by more than 30%, with a 9.8% loss in rotor thrust. Therefore, blowing near the trailing edge may be considered a promising approach for active BVI noise control.