The Experts below are selected from a list of 30 Experts worldwide ranked by ideXlab platform
Zarev Angel - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of Propeller inflow behaviour in non-axial operational regimes
2020Co-Authors: Zarev AngelAbstract:An experimental investigation has been performed to measure the inflow of two and four-bladed Propellers. This is conducted over a range of advance ratios (J = 0.36 to 1.54) and yaw angles (γ= 0 to 20◦) at a Reynolds number of Re≈111000, based on the chord length and advancing blade resultant velocity at the 70% spanwise position. Drawing on experimental results, three major qualitative trends are observed, that characterise the axial induced inflow of inclined Propellers: the formation of an approximately sinusoidal inflow trend around the azimuth featuring broad regions of increased and reduced inflow, an azimuthal phase shift of the trend from the advancing and retreating blade positions, and the dependencies of the inflow maxima, minima and phase shift on advance ratio, yaw angle and radial position. These are subsequently compared against two widely used assumptions for calculating the aerodynamic environment of inclined Propellers; firstly, that inflow at each radial and azimuthal elements calculated using an axial approximation of the whole Propeller Disc operating within the same condition as that element, and secondly, uniform induced inflow across the entire Propeller plane. The comparison demonstrates the limitations of said assumptions by highlighting their inability to account for components of the trailed and shed vortical systems of the Propeller wake. The results are also compared against CFD, demonstrating excellent consistency with the computational solution
Mogens Blanke - One of the best experts on this subject based on the ideXlab platform.
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nonlinear output feedback control of underwater vehicle Propellers using feedback form estimated axial flow velocity
IEEE Journal of Oceanic Engineering, 2000Co-Authors: ThorI I Fossen, Mogens BlankeAbstract:Accurate Propeller shaft speed controllers can be designed by using nonlinear control theory and feedback from the axial water velocity in the Propeller Disc. In this paper, an output feedback controller is derived, reconstructing the axial flow velocity from vehicle speed measurements, using a three-state model of Propeller shaft speed, forward (surge) speed of the vehicle, and the axial flow velocity. Lyapunov stability theory is used to prove that a nonlinear observer combined with an output feedback integral controller provide exponential stability. The output feedback controller compensates for variations in thrust due to time variations in advance speed. This is a major problem when applying conventional vehicle-Propeller control systems. The proposed controller is simulated for an underwater vehicle equipped with a single Propeller. The simulations demonstrate that the axial water velocity can be estimated with good accuracy. In addition, the output feedback integral controller shows superior performance and robustness compared to a conventional shaft speed controller.
Van Kuik G.a.m. - One of the best experts on this subject based on the ideXlab platform.
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On the velocity at wind turbine and Propeller actuator Discs
'Copernicus GmbH', 2020Co-Authors: Van Kuik G.a.m.Abstract:The first version of the actuator Disc momentum theory is more than 100 years old. The extension towards very low rotational speeds with high torque for Discs with a constant circulation became available only recently. This theory gives the performance data like the power coefficient and average velocity at the Disc. Potential flow calculations have added flow properties like the distribution of this velocity. The present paper addresses the comparison of actuator Discs representing Propellers and wind turbines, with emphasis on the velocity at the Disc. At a low rotational speed, Propeller Discs have an expanding wake while still energy is put into the wake. The high angular momentum of the wake, due to the high torque, creates a pressure deficit which is supplemented by the pressure added by the Disc thrust. This results in a positive energy balance while the wake axial velocity has lowered. In the Propeller and wind turbine flow regime the velocity at the Disc is 0 for a certain minimum but non-zero rotational speed. At the Disc, the distribution of the axial velocity component is non-uniform in all actuator Disc flows. However, the distribution of the velocity in the plane containing the axis, the meridian plane, is practically uniform (deviation < 0:2 %) for wind turbine Disc flows with tip speed ratio > 5, almost uniform (deviation 2 %) for wind turbine Disc flows with D 1 and Propeller flows with advance ratio J D, and non-uniform (deviation 5 %) for the Propeller Disc flow with wake expansion at J D 2. These differences in uniformity are caused by the different strengths of the singularity in the wake boundary vorticity strength at its leading edge. Wind Energ
Grönstedt Tomas - One of the best experts on this subject based on the ideXlab platform.
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A Conceptual Design Study of an Open Rotor Powered Regional Aircraft
2014Co-Authors: Larsson Linda, Lundbladh Anders, Grönstedt TomasAbstract:Today many of the routes between small to medium sized airports and large hubs are operated by regional aircraft, powered by turboprop or turbofan engines. In the future the open rotor engine might provide an alternative option. The open rotor would combine the possibility of high cruise speed with high propulsive efficiency. Also, since the open rotor essentially is a turboprop with the possibility to fly fast, there is a benefit of high specific range at low cruising speeds, thus giving it a wide range cruise operation. In this paper a regional aircraft for 70 passengers and 3000 km range is studied. The aircraft is evaluated with both a counter rotating open rotor and a turbofan engine. Aircraft design parameters such as wing area and sweep are varied together with engine parameters such as engine power and Propeller Disc loading. Results show that the open rotor aircraft has a 17.0 % higher specific range at the optimal cruise Mach number compared to the turbofan aircraft. For higher speeds, at Mach 0.78, the difference is reduced to 15.0 %. The long range cruise Mach number is around Mach 0.7 for the open rotor aircraft while for the turbofan aircraft it is slightly higher, around Mach 0.72
Palomino Alberto - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical Effects on Heated C/C-SiC Tubes: Development of a Validation Method
'Pisa University Press', 2090Co-Authors: Palomino AlbertoAbstract:The ceramic matrix composite (CMC) C/C-SiC has found many applications such as: Propeller Disc brakes, hot gas liners, re-entry nose cap, nozzles for rockets, jet vanes for thrust vector control of solid propellant rockets, and for spacecraft structures. In order to integrate this material in the designs for products in this field, the material must be properly characterized, and thermomechanical models associated with these designs must be validated with experimental values. At department of Ceramic Composites and Structures (BT-KVS) in the Institute of Structures and Design of DLR in Stuttgart, filament wound C/C-SiC structures are currently under development. A validation method was developed, which was specifically intended to validate thermomechanical FEM models of heated C/C-SiC tubes. Experiments were designed with special consideration of the modelling and simulation processes. Filament wound C/C-SiC tubes, and seam welded stainless steel tubes were used as samples in the investigation. The axial temperature distributions were measured along the inner and outer surfaces, and curves were fitted to the data in order to provide a thermal boundary condition in the models. The emissivity of several surfaces was determined over the temperature range of 200–800◦C during the experimental work, and these reference values were used to obtain the temperature of the sample from measurements made by using infrared spectrometry. The flow phenomena in the physical problem was studied by infrared imaging, and by using a projection shadowgraph method; these methods are presented in detail, and some examples that illustrate the methods’ usefulness are presented with the intention that they be used in future projects. CTscans made of the samples before and after the tests are presented and compared with a Discussion about the effects of oxidation, and relevant analytical models for porous flow are presented for future modelling of the oxidation processes. The radial displacement of the sample along the outer surface was measured by photogrammetry. This work includes the development of three analytical models for the thermomechanical structural problem; of which one was implemented in a script that provided results that were in close agreement with the simulation results; the results were of the same shape and order of magnitude as those measured by photogrammetry. An investigation was performed to determine the general trends of the stress and the radial displacement across the wall of a filament wound tube of similar geometry with different winding angle sequences. The general trends observed are explained, and the usefulness of the analytical model and the scripts created are presented. The agreement between the different facets of the investigation inspires confidence in that the validation method works, and that the analytical model produced is useful. Several reasons are suggested for the Discrepancy in the values obtained. Recommendations are made for future work as a continuation of the present work, and possible avenues for application of the tools hereby provided are suggested
