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Simulation of uncontrollable (“spontaneous”) rotation on a helicopter flight simulator
Get PDFThis paper presents the simulation predictions of the helicopter uncontrollable ("spontaneous") rotation obtained on the VPS-5 helicopter flight simulator. A special feature of the research was the use of the coefficients which take into account the tail rotor (TR) operation under uncontrollable rotation in the flight simulator mathematical model. During the simulation, the operator - pilot forced the helicopter into rotation about the vertical axis to the predetermined value of the rotation velocity (100 deg/sec, 120 deg/sec). After reaching the preset value of the rotation velocity, the operator-pilot recovered the helicopter from uncontrollable rotation by sharply kicking the right pedal to the hard stop. For these two regimes the yaw control power was shown and the comparison of the yaw control power with the minimum flying quality requirements was performed. The results of this study show that to prevent this helicopter from falling into uncontrolled rotation, it is necessary either to ensure the helicopter rotation rate limiting to the value at which the condition of generating the specified control power is met when fully kicking the right pedal or to increase the control power at a higher helicopter rotation rate
Impact of wake modeling uncertainty on helicopter rotor aeroacoustic analysis
No full textFree-wake models are routinely used in aeroacoustic analysis of helicopter rotors; however, their semi-empiricism is essentially accompanied with uncertainty related to physical wake parameters. In some cases, analysts have to resort to empirical adaption of these parameters based on previous experimental evidence. This paper investigates the impact of inherent uncertainty in wake aerodynamic modeling on the robustness of helicopter rotor aeroacoustic analysis. A free-wake aeroelastic rotor model is employed to predict high-resolution unsteady airloads, including blade-vortex interactions. A rotor aeroacoustics model, fundamentally based on Acoustic Analogy, is utilized to calculate aerodynamic noise in the time-domain. The individual analytical models are incorporated into a stochastic analysis numerical procedure, implemented through non-intrusive Polynomial Chaos expansion. The possible sources of uncertainty in wake tip-vortex core modeling are identified and their impact on noise predictions quantified. When experimental data to adjust the tip-vortex core model are not available the uncertainty in acoustic pressure and ground noise impact at observers dominated by blade-vortex interaction noise can reach up to 25% and 3.50 dB respectively. This work aims to devise generalized uncertainty maps to be used as modeling guidelines for aeroacoustic analysis in the absence of the robust evidence necessary for calibration of semi-empirical vortex core models
Learning-based clustering for Flight Condition Recognition
Get PDFThis paper presents flight condition recognition (FCR) algorithms for rotorcraft health and usage monitoring systems (HUMS), which are developed by using the clustering techniques of machine learning. Training and validation dataset are generated by using a generic nonlinear helicopter simulator and several flight data are obtained to train the algorithm. Gaussian Mixture Model (GMM), Neural Networks (NN) and Logistical Regression (LR) algorithms are implemented to perform FCR analyses. Validation and comparison studies are performed and results are compared in terms of accuracy, execution and training time. Finally, a detailed flight report about the flight is provided with percentages of performed flight conditions, which is used to provide feedback for health and usage monitoring systems to predict the life of the aircraft components
Dynamic inflow model for hovering rotors in non-parallel ground effect
Get PDFThis paper presents a state-space dynamic inflow modeling method suitable for flight dynamics analysis of rotors in ground effect. Akin to the Pitt-Peters model, it relates inflow components to rotor loads as determined by a Vortex-Lattice-type numerical simulations, and may be applied to non-parallel rotor-ground configurations as well as to moving ground cases. Here, the model is identified for three flight hovering cases (far from the ground, near a parallel ground and near an inclined ground) and compared with a set of validation data, highlighting the capability of the proposed methodology to reproduce the main features of the inflow
Topology optimization in rotorcraft applications
Get PDFTo introduce a new design nowadays the engineer has to show, that it provides a significant leap in performance improvement, not only a minor step. This is the reason why new technologies are implemented as those currently used are close to the border of optimization. Among other technologies, which will certainly be widely used in future aerospace, is 3D printing. As parts are expected to be lighter and maintain the same structural strength, the best solution to produce complicated shapes is to print it out. This allows to produce complicated shapes, that can have closed, empty spaces, what provides significant mass reduction. The paper will concentrate on the manner of constructing parts ready for printing with optimization process implemented. A brief description of topology optimization helps to understand the data connections between design and manufacturing. The process of optimization is clarified with respect to construction requirements. Some strategies of optimization and different approaches to designed alike elements are shown. Conclusions present the status of the work and expected future results along with key examples enclosed. All the presented work was based on the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreements No 737955 and No 755483
Rotor wake and inflow characteristics of multirotor drone configurations
Get PDFA coordinated experimental and computational study of multirotor configurations has been carried out at low Reynolds numbers. The configurations include coaxial rotors, horizontally spaced side-by-side rotors, and tandem rotors separated by horizontal and vertical spacing, both. The calculations have been done at a nominal total thrust coefficient of 0.008. Although rotor performance, tip vortex trajectories, and flow velocity distributions are all of interest, the present study has focused on the inflow velocity field at a number of planes immediately above and below the rotor disks, for the express purpose of developing reduced order inflow models. Test data and the computations for the time averaged inflow and outflow fields compare well with each other. Significant rotor-wake interaction phenomena are seen due to the close proximity of the rotor disk, even when the rotors are in hover. Dynamic inflow coefficients have been extracted for representative strong rotor-vortex interaction scenarios
Unsteady boundary-layer transition measurements and computations on a rotating blade under cyclic pitch conditions
Get PDFThe presented work tackles the lack of experimental investigations of unsteady laminar-turbulent boundary-layer transition on rotor blades at cyclic pitch actuation, which are important for accurate performance predictions of helicopters in forward flight. Unsteady transition positions were measured on the blade suction side of a four-bladed subscale rotor by means of the non-intrusive Differential Infrared Thermography (DIT). Experiments were conducted at different rotation rates corresponding to Mach and Reynolds numbers at 75% rotor radius of up to M75 = 0:21 and Re75 = 3:3 x 105 and with varying cyclic blade pitch settings. The setup allowed to measure transition across the outer 54% of the rotor radius. For comparison, transition was also measured using conventional infrared thermography for steady cases with collective pitch settings only. The study is complemented by numerical simulations including boundary-layer transition modelling based on semi-empirical criteria. Promising results reveal a plausible development of measured transition positions over the pitch cycle, a reasonable comparison to experimental results obtained using the already established ?Cp method, and noticeable agreement with numerical simulations. The result is the first systematic study of unsteady boundary-layer transition on a rotor suction side by means of DIT including a comparison to numerical computations
Aerodynamic and blade vortex interaction noise characteristics analysis of electrically controlled rotor based on viscous vortex particle method
Get PDFAn electrically controlled rotor (ECR), also called a swashplateless rotor, replaces a swashplate with a trailing edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of an ECR in blade-vortex interaction (BVI) condition, an analysis model based on the viscous vortex particle method, ECR blade pitch equation and Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The flap motion induced blade pitch movement is obtained by solving the ECR blade pitch movement equation via the Runge-Kutta fourth-order method. On the basis, BVI noise radiation of an ECR is evaluated using the Ffowcs Williams and Hawkings (FW-H) equation. Based on the present prediction model, the aerodynamic and acoustic characteristics of a sample ECR in BVI condition are analyzed. The results show that since the BVI event of the ECR on the advancing side is mainly caused by the interaction between the flap tip vortex and the blade, the blade spanwise range of ECR BVI occurrence on the advancing side is smaller than that of the conventional rotor. In addition, the magnitude of the maximum sound pressure level on the advancing side as well as on the retreating side of the ECR is also different from that of the conventional rotor, which is consistent with the difference in the airloads between the ECR and conventional rotor
A panel free-wake code with boundary layer method for helicopter simulations
No full textUPM, DLR's unsteady panel and free-wake code for helicopter simulations, is being modernized and extended in order to provide a modern mid-fidelity tool suitable to support the industrial helicopter development process. Two major tasks in this process were the implementation of approximate boundary layer analysis methods and the calculation of unsteady pressures on arbitrary bodies. This paper shortly describes UPM and the newly implemented methods. Then, results of verification and validation calculations are presented, including isolated airfoil, wing, rotor and fuselage test cases. Finally, a complete helicopter configuration is simulated and compared to experimental wind tunnel results of the GOAHEAD campaign. The results show that the approximate boundary layer methods are able to identify flow separation regions and provide reasonable friction force estimates for a wide range of applications. Nevertheless, the limits of the methods be-come apparent in cases where viscous effects lead to strong nonlinear behavior. The complete helicopter simulation also shows a good agreement with experimental data in general. But here, too, individual flow re-gions reveal the limits of the underlying theory. If these limits are kept in mind, UPM can be a valuable tool and support the helicopter development process in many regards
Propagation of material and manufacturing uncertainties in composite helicopter rotor blades
No full textThe effects of material and manufacturing uncertainties of a composite UH-60A helicopter rotor blade on the beam properties, the rotating natural frequencies, the aeroelastic response and vibratory loads in hover and in forward flight are studied. The multidisciplinary rotor blade design framework of this study consists of three main components (DYMORE, VABS and the structural preprocessor SONATACBM) that are wrapped into the OpenMDAO open-source computing platform for system analysis and multidisciplinary optimization. Two separate Monte-Carlo simulations are performed with 1000 samples each. Both material and manufacturing uncertainties propagate through all levels of the simulation, resulting in substantial impacts on natural frequencies, elastic blade tip response and the 4/rev vibratory hubforces