Open Rotor Research Articles

Introduction of oblique plane waves through a forcing source term in Euler equations

The propagation of shock waves generated by a transonic flow at the tip of a propeller blade is numerically calculated in order to determine the pressure footprint on an aircraft fuselage. An academic case is first proposed to validate the methodology. An incoming signal is built up as oblique harmonic plane waves. The signal is introduced in the computational domain using a Gaussian volume forcing term in the conservation of mass and energy equations. The Euler equations are solved in two dimensions using finite-difference schemes with low dispersion and dissipation. Selective filtering has also been integrated in the algorithm to remove grid-to-grid oscillations. The numerical solution is compared to an analytical solution based on the tailored Green function. An illustration for a realistic open rotor is then considered. The pressure signal near the blade tip, determined from a preliminary RANS simulation, is introduced using a volume source in a solver of the Euler equations.

Aerodynamic and aeroacoustic sensitivities of contra-rotating open rotors to operational parameters

Abstract Open rotors can play a critical role towards transitioning to a more sustainable aviation by providing a fuel-efficient alternative. This paper considers the sensitivity of an open-rotor engine to variations of three operational parameters during take-off, focusing on both aerodynamics and aeroacoustics. Via a sensitivity analysis, insights to the complex interactions of aerodynamics and aeroacoustics can be gained. For both the aerodynamics and aeroacoustics of the engine, numerical methods have been implemented. Namely, the flowfield has been solved using unsteady Reynolds Averaged Navier Stokes and the acoustic footprint of the engine has been quantified through the Ffowcs Williams-Hawking equations. The analysis has concluded that the aerodynamic performance of the open rotor can decisively be impacted by small variations of the operational parameters. Specifically, blade loading increased by 9.8% for a 5% decrease in inlet total temperature with the uncertainty being amplified through the engine. In comparison, the aeroacoustic footprint of the engine had more moderate variations, with the overall sound pressure level increasing by up to 2.4dB for a microphone lying on the engine axis and aft of the inlet. The results signify that there is considerable sensitivity in the model and shall be systematically examined during the design or optimisation process.

An experimental study of noise generated by tandem blades

To facilitate the low-noise design of tandem lift bodies as applied in aeroengines and aircraft, the acoustic features of tandem blades are investigated by wind-tunnel experiments. This is further specialized for the rotating blades applied in contra-rotating open rotors under the concept of frozen-rotor. A 70-channel phased microphone array and nine high-precision free-field microphones are employed. The beamforming method, enhanced by a source filtering technique, is employed to locate noise sources, providing insights into the source patterns of blade-blade interaction noise concerning flow speed, blade spacing, and aft blade clipping. The results show the following: (A) Sources of tandem-blade noise exist in the form of concentrated source clusters, resulting in two major clusters: the mid-span interaction noise and the tip-induced noise. (B) These source clusters tend to separate as flow speed or blade spacing increases. (C) By increasing blade spacing, the band-pass filtered overall sound pressure level is reduced by 2.9 dB. (D) A two-phase noise suppression pattern is observed with blade clipping, resulting in a total reduction of 3.0 dB for the interaction noise through the removal of tip-induced noise sources and the replacement of mid-span noise sources. Based on these findings, suggestions concerning blade spacing and clipping are discussed.

Effect of leaned blades on the aerodynamic performance of contra-rotating open rotor

Effect of leaned blades on the aerodynamic performance of contra-rotating open rotor

Efficient Surrogate-based Optimization of the Aerodynamic Performance of a Contra-rotating Open Rotor Utilizing an Infilling Criterion

Efficient Surrogate-based Optimization of the Aerodynamic Performance of a Contra-rotating Open Rotor Utilizing an Infilling Criterion

Digital Simulation of Coupled Dynamic Characteristics of Open Rotor and Dynamic Balancing Test Research

An aero engine, as the core power equipment of the aircraft, enables safe and stable operation with a very high reliability index, and is an important guarantee in flight. The open rotor turbine engines (contra-rotating propeller) have stood out as a research hotspot for aviation power equipment in recent years due to their outstanding advantages of low fuel consumption, high airspeed, and strong propulsion efficiency. Aiming at the problems of vibration exceeding the standard generated by imbalance during the operation of the dual-rotor system of aircraft development, the difficulty of identifying the coupled vibration under the micro-differential speed condition, and the complexity of the dynamic characteristic law, a kind of numerical simulation of the dynamics based on the finite element technology is proposed, together with an experimental research method for the fast and accurate identification of the coupled vibration of the dual-rotor system. Based on the existing open rotor engine structure design to build a simulation test bed, establish a double rotor finite element simulation digital twin model, and analyze and calculate the typical working conditions of the dynamic characteristics of parameters. The advanced algorithm of double rotor coupling vibration signal identification is utilized to carry out decoupling and dynamic balancing experimental tests, comparing the simulation results with the measured data to verify the accuracy of the technical means. The results of the study show that the vibration suppression rate of the finite element calculation simulation test carried out for the simulated double rotor is 98%, and the average vibration reduction ratio of the actual field test at 850 rpm, 1000 rpm, and 3000 rpm is over 50%, which achieves a good dynamic balancing effect, and has the merit of practical engineering application.

Improving vertical-axis wind turbine performance through innovative combination of deflector and plasma actuator

Vertical-axis wind turbines (VAWTs) are efficient tools for harvesting wind energy, especially in urban areas; however, aerodynamic losses owing to dynamic stall and negative torque reduce their efficiency. Therefore, it is necessary to use flow-control methods for VAWTs. In the present study, a two-dimensional VAWT is numerically modeled and simulated. Subsequently, a novel combined actuator is proposed to improve the performance of VAWT. This novel combined actuator included plasma actuators and deflector plate as active and passive actuators, respectively. First, 16 cases were examined to determine the optimal deflector angle and distance. In the best case, the deflector with an angle of 45° and a radius ratio of 3.3 increased the power coefficient by 13.37% compared to the open rotor. Then, the effect of the combined use of the deflector and plasma actuator was investigated. The results showed that the activation of the plasma actuator from an azimuth angle of 55° to 145° increased the power coefficient by 45.68% in comparison to the open rotor. Considering the energy consumed by actuators, the net energy produced by the VAWT per rotation cycle increased by 26.72% compared to the open rotor.

Turbulence ingestion noise generation in rotating blades

The interaction between ingested turbulence and rotating blades is a key source of broadband noise in engineering applications. In this paper, a far-field noise model accounting for source correlation across the span of the blade and between blades is developed and applied to the study of homogeneous isotropic turbulence ingestion by a model cooling fan, wind turbine and aircraft propeller. The widely used theory of Amiet is revisited and it is shown that previous works produce conflicting results when attempting to account for blade-to-blade correlation. Central to the model is the calculation of the time between blade chops of the same turbulent eddy as heard by the observer. In this paper it is shown that, when derived correctly, Amiet's theory accounts for correlated sources between blades and, thus, can predict haystacking tones. Comparisons with the new rotational formulation and with experimental data enable us to show that Amiet's theory can be used to accurately predict turbulence ingestion noise from open rotors. In particular, it is found that the infinite-span assumption in strip theory and the neglect of correlation effects across the span do not undermine the accuracy of this theory. This is of great importance because, unlike Amiet's theory, models which treat rotational effects and source correlation exactly are expensive to evaluate routinely at high frequencies due to the slow convergence of infinite series with Bessel functions.

Development and Application of Open Rotor Discrete Noise Prediction Program Using Time-Domain Methods

The aerodynamic noise of an open rotor is one of the critical challenges that must be considered in its design and application. FODNOPP, a program specifically programmed to predict the aerodynamic discrete noise of single- and counter-rotating open rotors (such as propellers, propfans, and rotorcraft rotors) at subsonic, transonic, and supersonic helical blade tip speeds, has recently been developed by the first author. This program is composed of four prediction codes, namely code a1, code a2, code b, and code c, each based on Farassat-derived formulations Formu 1-RTE, Formu 1A, Formu 1-Sph, and Formu 3, providing time-domain solutions to the Ffowcs Williams–Hawkings equation. Four verification examples for both propeller low-speed flight noise and counter-rotating propfan take-off noise are presented, along with an application case for transonic helical tip speed counter-rotating propfan cruise noise. The results demonstrate the accuracy of FODNOPP in calculating the noise for these verification cases. And in the counter-rotating propfan cruise noise case, the maximum harmonic sound pressure level of the rear propfan is 5.5 dB higher than that of the front propfan. FODNOPP can be referred to as a comprehensive design tool, and it offers valuable guidance for engineering design focused on rotor-related noise reduction.

Aerodynamic Investigation of Shrouded Rotors with Dual Exit Channels

The growing need for rotary-wing aerial vehicles with high-speed forward movement and dependable hover performance is critical in various applications. Shrouded rotors enhance aerodynamic performance, create more overall thrust with the same power consumption as open rotors, and have a more uniform induced velocity flow field. This paper presents a parametric computational investigation centered on the hypothesis, that dividing the shroud exit channel into convergent inner and divergent outer channels would enhance flow uniformity, reducing power losses, and preventing airflow separation from the main shroud’s inner walls. The validity of this hypothesized concept is demonstrated through extensive Computational Fluid Dynamic (CFD) simulations. The paper includes a case analysis utilizing experimental data from a highly- maneuverable drone, named Navig8, equipped with a 9-inch shrouded propeller where various shrouded configurations are examined using Computational Fluid Dynamics. Results typically show an increase in total thrust with the incorporation of an inner shroud for a given power.

An efficient hybrid aeroacoustic method to predict the noise of a ducted coaxial-rotor UAV

Ducted coaxial-rotor UAV is a new concept UAV configuration. Compared with the traditional open rotor UAV, it has the advantages of higher safety, lower noise and smaller size, especially suitable for compact space and low noise scene applications. However, the complexity of the internal flow field caused by the presence of the duct makes it difficult to obtain accurate acoustic results by using the conventional aeroacoustic simulation methods. Based on the theory of duct acoustics and the theory of propeller noise, this paper presents an efficient calculation method of aeroacoustic source suitable for the configuration of a ducted UAV. The aeroacoustic source of a ducted coaxial-rotor UAV independently developed by the current research group is studied, and the duct acoustic mode components excited by the aeroacoustic source of the UAV are obtained. The results show that the distribution of the duct mode excited by the aeroacoustic source of the ducted UAV has a strong correlation with the number of propeller blades, and the main characteristic modes dominate the acoustic source of the UAV.

Unsteady Reynolds-Averaged Navier–Stokes Simulations of a Ducted Wind Turbine

Abstract An unsteady Reynolds-averaged Navier–Stokes model on body-fitted meshes in a commercial package (SimericsMP+) with a mismatched grid interface is used to study fluid dynamics around a ducted wind turbine. The model is validated by studying turbulent flow past a marine propeller. The nondimensional thrust and torque coefficients are compared against experimental data and results from a large eddy simulation model. Both coefficients are found to be within 3% of experimental results. Following this validation, the impact of different tip speed ratios on the ducted wind turbine's fluid dynamics is assessed. The optimal tip speed ratio is found to be the design value of 3.93 with a maximum power coefficient of 0.465 based on the duct exit area. The corresponding thrust coefficient is found to be 1.02 based on the rotor area. Lower tip speed ratios experience larger flow separation on the duct interior. Higher tip speed ratios decrease the size of the low-velocity region behind the hub. The ducted wind turbine's performance at design conditions is compared to an open rotor. The ducted wind turbine increases the power coefficient by 96% over the open rotor. The impact of hub size on the ducted wind turbine is also studied by simulating a smaller hub with 77% diameter. At the design tip speed ratio, the smaller hub has a power coefficient of 0.417. The maximum power coefficient is found to be 0.446 at a higher tip speed ratio of 4.5.

Mistuning Sensitivity of a Fan Bladed-Disk With Geometrical Nonlinearities

Abstract In order to decrease their environmental impact, turbo-engine manufacturers tend to increase the span of fan blades while maintaining a slender profile. This design leads to more pronounced geometrical nonlinear effects. Computing the frequency response function of such structures is complicated due to the size of their associated finite element model. Classical substructuring approaches are no longer efficient to reduce the size of the problem as all the nodes of the system must be kept since they experience nonlinear behaviors. Different reduction methodologies have been defined in the past decades to tackle such nonlinear systems. Among these strategies, the direct normal form (DNF) extends the theory of normal form to finite element models. This methodology is here applied to a single blade model. Based on the assumption of a fairly rigid disk and the cyclic symmetric properties, a full cyclic symmetric reduced-order model is computed. In this work, this methodology is extended to account for random mistuning. Such a strategy allows to perform, for instance, fast parametric studies. This paper studies the sensitivity of the random mistuning on a nonlinear open rotor system in order to help turbo-engineers in their design phase. Three ranges of the excitation level are studied. At a low level of excitation, the system is close to the linear case. For higher forcing amplitude, a high amplification factor (AF) due to the merge of an isolated branch is observed, which is detrimental for the structure. For the last range (containing the highest forcing amplitudes), the nonlinearities are highly activated, and low values of the amplification factor are obtained due to the spread of the vibrational energy over the frequency range.

Diffuser augmented wind turbines: A critical analysis of the design practice based on the ducting of an existing open rotor

The study investigates the soundness of a popular uncoupled design strategy for diffuser-augmented wind turbines (DAWTs), namely the use of an annular wing to enclose an existing open-rotor. To this aim, the paper presents a numerical analysis of the NREL-Phase-VI rotor enclosed into a shroud whose cross-section consists of the Selig-S1223 airfoil. Particular attention is devoted to the analysis of the blade pressure fields, velocity triangles, blade forces, tip-vortex and wake development. The data show that the duct induces a gain in the rotor inlet axial velocity and, therefore, in the local flow-angle. Consequently, the blade forces, the extracted work, and the risk of flow separation considerably rise. Thanks to the simultaneous increase in the ingested mass flow rate and extracted work, the DAWT experiences a higher power coefficient (CP,exit) which, however, would be further improved if a coupled design-procedure was used. Indeed, in the present case, the maximum CP,exit is obtained for the wind-speed value corresponding to the duct optimal flow behaviour. However, in this condition, the rotor operates at off-design with an extensive flow-separation on the blade suction-side. Finally, while the inefficiencies magnitude is specific of the analysed case, the conceptual relevance of the achievements remains valid in general.

Variations with Mach number for gust–airfoil interaction noise

The interaction of turbulence with airfoil is an important noise source in many engineering fields, including helicopters, turbofans, and contra-rotating open rotor engines, where turbulence generated in the wake of upstream blades interacts with the leading edge of downstream blades and produces aerodynamic noise. One approach to study turbulence–airfoil interaction noise is to model the oncoming turbulence as harmonic gusts. A compact noise source produces a dipole-like sound directivity pattern. However, when the acoustic wavelength is much smaller than the airfoil chord length, the airfoil needs to be treated as a non-compact source, and the gust–airfoil interaction becomes more complicated and results in multiple lobes generated in the radiated sound directivity. Capturing the short acoustic wavelength is a challenge for numerical simulations. In this work, simulations are performed for gust–airfoil interaction at different Mach numbers using a high-fidelity direct computational aeroacoustic (CAA) approach based on a spectral/hp element method verified by a CAA benchmark case. It is found that the squared sound pressure varies approximately as the fifth power of Mach number, which changes slightly with the observer location. This scaling law can give a better sound prediction than the flat-plate theory for thicker airfoils. Furthermore, another prediction method, based on the flat-plate theory and CAA simulation, has been proposed to give better predictions than the scaling law for thicker airfoils.

Software Package for Calculating the Noise Generated by Open Rotors

Software Package for Calculating the Noise Generated by Open Rotors

ДИНАМИЧЕСКАЯ ИДЕНТИФИКАЦИЯ ПАРАМЕТРОВ СХЕМЫ ЗАМЕЩЕНИЯ АСИНХРОННОГО ДВИГАТЕЛЯ НА ОСНОВЕ БАЛАНСА МГНОВЕННОЙ ПОЛНОЙ МОЩНОСТИ В УСТАНОВИВШЕМСЯ РЕЖИМЕ

The relevance Automated electric drive (AED) is one of the most important and most common control objects in automatic process control systems (ACS). The control of the output coordinate in the AED, for the implementation of feedback with an automated process control system, can be carried out both with the help of a speed sensor and without it, using the computing power of a frequency converter included in the AED. For the sensorless AED to work in an automated process control system, it is necessary to ensure adequate restoration of the vector of state variables of the induction motor (IM) in the frequency converter using a configurable mathematical model. To restore the vector of state variables, it is necessary to select coefficients in the system of differential equations that correspond with some error to the electrical parameters of the BP replacement circuit, i.e. to carry out the identification procedure. In fact, the procedure for determining the parameters of the PS is the process of finding the extremum of the objective function, built on the basis of data obtained during the operation of the PS. In electrical engineering, numerical methods for finding the extremum of the objective function have become widely used to identify parameters, but these methods have significant limitations and disadvantages. The problem of using numerical methods to find the extremum of an objective function with two or more arguments in AED microprocessor control systems is that it is necessary to calculate partial derivatives in discrete form for each argument of the function. Calculation of partial derivatives in ideal systems without noise and disturbances is a proven and easy-to-implement process, but noise and disturbances are present in real microprocessor systems. Because of this, when calculating partial derivatives for each argument, the probability of breakpoints of the first and second kind increases, the struggle with which presents a certain difficulty. One of the classes of methods that allow determining the extremum of an objective function without finding partial derivatives are metaheuristic algorithms, and in particular genetic algorithms. Aim of research Experimental study of the efficiency of a genetic algorithm in the problem of dynamic identification of parameters of an induction motor circuit with an open rotor winding without stopping and decommissioning an electrical complex. Research methods Metaheuristic algorithms, iterative procedures, genetic algorithm, discrete systems, optimization methods. Results The effectiveness of the genetic algorithm was experimentally tested and proved in the problem of dynamic identification of parameters of the induction motor replacement circuit with an open rotor winding without stopping and decommissioning the electrical complex.

Interaction tonal noise generated by contra-rotating open rotors

Fast and accurate prediction of sound radiation of Contra-Rotating Open Rotors (CRORs) is an essential element of design methods of low-noise open rotor propulsion systems. In the present work, a previous frequency-domain model is extended to predict CROR noise. It builds explicitly the relationship between harmonic loadings and corresponding tonal noise, by which the influential parameters to noise generation can be clearly understood. The real distributions of steady and unsteady blade loadings are calculated by the Nonlinear Harmonic (NLH) method. In the present hybrid approach, both the CFD and acoustic modules are solved in the frequency domain. To assess the accuracy of the developed method, the loading noise of a CROR is calculated and compared against results by using the time-domain FW-H module of NUMECA. The predicted sound directivities by the two methods are in good agreements. The present acoustic model in the frequency domain is proven to be accurate and have high efficiency in far-field noise prediction and data processing. Furthermore, the characteristics of the CROR interaction tonal noise are analyzed and discussed.

Historical development of the coaxial contra-rotating propeller

AbstractWe review the development of the contra-rotating propellers from the origins to the present. Initially, these systems were proposed to increase speed, then to increase propulsive efficiency, and thus reduce fuel burn. Ultimately, they hit another environmental limit: too much noise. Acoustics has been in fact the main focus of the development in the past 30 years. Pioneering work done across countries demonstrated several unique features of this propulsor. Various embodiments are available, namely contra-rotating, counter-rotating, co-axial, tandem, open rotor and prop-fans, collectively named contra-rotating propellers. This review only considers concepts that have been applied to real aircraft, prototypes that are known to have been flight tested (about 70 vehicles), or representative laboratory models. Five classifications are proposed: pioneers (before 1940), golden years (1940–1950), Western airplanes (1950s onwards), Soviet-Russian airplanes (1950s onwards) and modern developments (1980s onwards). Selected experimental aircraft and laboratory concepts are mentioned, where these appear to advance the state-of-the-art. Power plants evolved from internal combustion engines to the modern gas turbine engines requiring new solutions. Engine layouts and propulsion configurations are analysed where appropriate. It is concluded that propulsive efficiency can only be achieved at a cost of multiple engineering problems, some of which remain unsolved.

Performance analysis of a vertical axis wind turbine using computational fluid dynamics

Vertical axis wind turbines (VAWTs) have gained popularity in the last few decades due to their numerous advantages when deployed in urban areas. Despite this, Vertical axis wind turbines have complex aerodynamics, dynamic stall, hence lower performance. Low/zero starting torque, noise, visual impact, as well as blade safeness are further hurdles when they are fitted into the physical environment. Due to these pertinent issues that comes to play in a vertical axis wind turbine, the current investigation explores an augmented vertical axis wind turbine (AVAWT) having a rotor and a stator. The outcome of the study highlighted the effect of mesh density and the type of turbulence model selected in the determination of the forces being exerted on the blade using computational fluid dynamics. Investigation into the effect of time steps showed lesser effect of this parameter on the performance of the blade computationally. The newly developed augmented turbine blades improved the output power by 1.35 times in comparison to an open rotor. The shape for the conical surface and the stator blade impacted the performance as well. Furthermore, it was deduced that there was higher dynamic stall for scenarios where the tip speed ratios were lower. The study showed the importance of the stator in a vertical axis wind turbine in ensuring that the incoming wind attains some acceleration as well as creating a lower pressure outlet but overall aids in the improvement of the power and torque coefficients by more than 36%.