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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Předběžný návrh malého dvoumístného vrtulníku / Preliminary Design of a Small Two Seat Helicopter

Junas, Milan January 2016 (has links)
The thesis deals the preliminary draft of the small two-seat helicopter with a piston engine. The aim of the thesis is not to propose a helicopter across the extent of the problems. Therefore we have chosen only selected issues which can be managed in the range of work. The introduction is focused on defining the general requirements imposed on proposed helicopter, formulating the basic conceptual and structural design according to the building regulation the relevant category. These ranges create a based assumption for right evaluation of the statistical analysis of the helicopters of the same or very near parameters category. Subsequently, there were defined the basic parameters of the proposed helicopter which make possible to solve the performance characteristics in the vertical and backward flight. The work is also focused on design of the rotor head of main rotor for the proposed helicopter, the definition of load acting on the rotor head, waving analysis and calculation of centrifugal forces acting on the main rotor blades. The design of the rotor head and also the helicopter as a whole will be graphically processed in the program Dassault Systemes Catia.
2

Computational Investigation of the Effects of Rotor-on-Rotor Interactions on Thrust and Noise

Schenk, Austin R 10 June 2020 (has links)
Recent advancements in electric propulsion systems have made electric vertical takeoff and landing aircraft a reality, and one that is seen as a partial solution to the growing issue of urban traffic congestion. Designing an aircraft with multiple smaller motors and rotors spread across the wings–referred to as distributed electric propulsion (DEP)–has shown great potential in help- ing improve electric aircraft performance by offering increased propulsive efficiency, augmented lift, and structural load distribution. For these reasons, DEP is one configuration that is currently being implemented into multiple prototype designs (e.g. NASA’s Maxwell X-57, Airbus Vahana, Opener BlackFly, and Joby S2). However, while a DEP configuration has many potential benefits, it complicates the aerodynamics by introducing complex rotor-on-rotor interactions which can significantly affect noise generation. In this study we use unsteady Reynolds-averaged Navier–Stokes (RANS) simulations (STAR-CCM+) with an aeroacoustic solver (PSU-WOPWOP) to quantify thrust fluctuations and noise generation for two distinct rotor-rotor configurations. The configurations investigated in this study are: 1) coplanar rotors with a varying tip separation distance and 2) one rotor downstream of the other at varying distances for a fixed tip separation distance. Both configurations are investigated using an APC 10x7E and DJI-based 0.24 m rotor. It was found that tip-to-tip separation distance has a stronger influence on noise generation than the downstream separation distance does. A one diameter change in tip separation distance resulted in a ∼15 dBA change in noise while a three diameter change in downstream separation distance only resulted in a ∼9 dBA change in noise for the same rotor. Changes in thrust fluctuations were found to predict trends in noise generation well for multi-rotor configurations. Additionally, it was shown that when rotors are located less than 10% of the diameter apart from each other, noise can be decreased by up to 9 dBA by moving one rotor ∼0.5 diameter downstream of the other.
3

Rotor dynamic analysis of 3D-modeled gas turbinerotor in Ansys

Samuelsson, Joakim January 2009 (has links)
<p>The world we are living in today is pushing the technology harder and harder. The products need to get better and today they also need to be friendlier to the environment. To get better products we need better analysis tools to optimize them and to get closer to the limit what the material can withstand. Siemens industrial Turbomachinery AB, at which thesis work is made, is constructing gas and steam turbines. Gas and steam turbines are important in producing power and electricity. Electricity is our most important invention we have and most of the people are just taking electricity for granted. One way to produce electricity is to use a gas turbine which is connected to a generator and by combing the turbine with a steam turbine the efficiency can be up to 60 %. That is not good enough and everybody want to get better efficiency for the turbines, meaning less fuel consumption and less impact on the environment.</p><p>The purpose of this thesis work is to analyze a tool for rotor dynamics calculations. Rotor dynamics is important in designing a gas turbine rotor because bad dynamics can easily lead to disaster. Ansys Classic version 11 is the analyze program that is going to be evaluated for the rotor dynamic applications. Nowadays rotor dynamics is done with beam elements i.e. 1D models, but in this thesis work the beam elementsare going to be changed to solid elements. With solid elements a 3D model can be built and thanks to that more complex calculations and simulations can be made. For example, with a 3D model 3D effects can be shown and e.g. simulations with blade loss can be done. 3D effects are not any problem today but in the future the gas turbines have to get better and maybe also the rotational speed will increase.</p><p>Ansys isn’t working perfectly yet, there are some problems. However Ansys have a good potential to be an additional tool for calculations of rotor dynamics, because more complex calculations and simulations can be done. More knowledge and time needs to form the rules to modeled a rotor and developing the analysis methods. Today the calculated lateral critical speeds are lower than the ones obtained from the in-house program Ardas version 2.9.3 which is used in Siemens Industrial Turbomachinery AB today. The difference between the programs are not so big for the four first lateral modes, only 3-8 %, but the next three lateral modes have a difference of 10-20 %. The torsion frequencies from Ansys are the same as the ones from Ardas, when the Solid186 elements are used to model the blades.</p>
4

Předběžný návrh malého šestimístného vrtulníku s jedním turbohřídelovým motorem / Design of the six seat helicopter with one turboshaft engine

Nasibullin, Bulat January 2020 (has links)
The aim of this work is to develop a preliminary design of a six-seat helicopter with a turboshaft engine. The preliminary design of the helicopter consists of processing statistical data on similar helicopters, which are then, based on the specified requirements, used to estimate the basic weight parameters of the helicopter, the main geometric parameters and to determine the type and power of the propulsion unit. It consists of calculations of basic geometric parameters of the aircraft and engine selection. Part of another solution is the aerodynamic calculation of the supporting rotor, from which both the performance of the helicopter in suspension and in forward flight flow. In a special part of the project, the attention is paid to the system of balancing the reaction torque, in this case fenestrone and the solution is supplemented by some specific means installed on the tail beam, which help to balance the reaction torque and improve the directional control parameters of the helicopter.
5

Vibration control in rotating machinery using variable dynamic stiffness hydrostatic squeeze-films

Roach, M. P. January 1990 (has links)
No description available.
6

An experimental and a theoretical investigation of rotor pitch damping using a model rotor

Sotiriou, C. P. January 1990 (has links)
No description available.
7

A theoretical study of rotor forces and torques in helical twin screw compressors

You, Cheng Xiang January 1994 (has links)
Helical twin screw compressors are being increasingly used in the oil and gas process industry and for refrigeration and air conditioning duties. This machine is capable of high reliability. To achieve it both thermodynamic efficiency and rotor forces must be taken into consideration at the design stage. In this study, a computer program for analysing the forces in a twin screw compressor has been developed. It takes into account all significant factors and includes a rotor profile generation program and a geometrical characteristics calculation program. The programs developed have been integrated with an existing performance simulation program and used to investigate several design aspects of a refrigeration twin screw compressor and an unusual refrigeration system design. A comprehensive examination of lobe tip designs suggests that lobe tip design parameters must be optimised if minimum power consumption is to be achieved and the use of a sealing strip gives an advantage. A para meter study for optimum rotor geometrical parameter combinations has shown that the 4+5 and 5+6 combinations have in general high efficiencies, but less rigidity, while the 5+7 and 4+6 combinations give the opposite results. The highest wrap angle and length/diameter ratio do not always lead to the highest compressor performance. A comprehensive examination of the influence of the slide valve on compressor performance and bearing forces has been conducted. Procedures for determining the optimum slide stop and volume ratios are presented. The detrimental effect of the non-return valve in a refrigeration system driven by a twin screw compressor has been examined. A non-reversing clutch fitted to the prime mover is an alternative, but must be designed according to the shut down torque which is higher than the normal running torque. This is demonstrated. An analytical model for axial-torsional coupled vibration in an Oil-injected twin screw compressor has been created. A frequency analysis of all the excitations has been conducted by using an FFT technique. It is found that the fundamental harmonic dominates the gas torque, while the first two harmonics dominate the axial forces.
8

Calculation of the pressure distribution on a pitching airfoil with application to the Darrieus Rotor

Ghodoosian, Nader 28 September 1983 (has links)
An analytical model leading to the pressure distribution on the cross section of a Darrieus Rotor Blade (airfoil) was constructed. The model was based on the inviscid flow theory and the contribution of the nonsteady wake vortices was neglected. The analytical model was translated into a computer code in order to study a variety of boundary conditions encountered by the rotating blades of the Darrieus Rotor. The results of the program indicate that for a pitching airfoil, lift can be adequately approximated by the Kutta-Joukowski forces, despite notable deviations in the pressure distribution on the airfoil. These deviations are most significant at the upwind half of the Darrieus Rotor where higher lift is accompanied by increased adverse pressure gradients. It was also found that the effect of pitching on lift can be approximated by a linear shift in the angle of attack proportional to the blade angular velocity. Finally, the fluid velocity about the pitching-only NACA 0015 was tabulated; thus allowing the principle of superposition to be used in order to determine the fluid velocity about a translating and pitching airfoil. / Graduation date: 1984
9

The effects of torsional-lateral coupling on the dynamics of a gear coupled rotor

Emery, Michael Aaron 25 April 2007 (has links)
This thesis focuses on the torsional-lateral interactions seen in gear coupled rotors. Of particular interest are cases where the torsional stiffness parameters affect the lateral critical speeds and where lateral stiffness and damping parameters affect torsional critical speeds and amplitudes. A common procedure for critical speed calculations has been to solve lateral and torsional systems separately. This procedure is tested through an eigenvalue analysis. It is shown in this thesis, however, that torsional-lateral interactions play major roles in each other's critical speeds. Some research has seemingly uncoupled two lateral degrees of freedom from the gear system by choosing bearing forces and a coordinate system pointing along the line of action and normal to the line of action. This simplification method has been tested for cases when the lateral bearing stiffness becomes asymmetric. The force generated by a rotating imbalance also creates a variable moment arm as the center of mass rotates about the geometric center of the gear. This variable moment arm is commonly neglected, but is included in the last case study and its effects are displayed in the results section of this thesis.
10

Study of compressible flow through a rotating duct

Karpatne, Anand 17 September 2015 (has links)
Several rotorcraft applications such as circulation control and tip jet driven rotors involve internal spanwise flow along the interior of a rotor blade. This dissertation describes a quasi 1-D numerical model of unsteady flow through a duct rotating about one end along with experimental validations. The numerical model is suitable for inclusion in the conceptual design stage for helicopter rotor blades with internal spanwise flow. To this end, centrifugal as well as coriolis effects, frictional losses, duct sweep and time-dependent duct boundary conditions are modeled, and a spanwise flow control valve can be included. One dimensional Euler equations are solved inside the duct using a finite volume formulation in which the advective fluxes are approximated using the Advective Upwind Splitting Method (AUSM). The model is used to explore the behavior of flow inside a 2 m long duct with a circular crosssection, rotating at tip speeds of up to 260 m/s. In the inviscid limit, at a rotor tip speed of 213 m/s, the model predicted the evolution of a shock which showed periodic oscillations with a time period of approximately 17.5 rotor revolutions. However, when friction was included, a shock did not form until the rotor tip speed was ~ 260 m/s. The effects of suddenly opening a flow control valve at different spanwise stations, x [subscript valve] = 0.0R, x [subscript valve] = 0.5R and x [subscript valve] = R, were also studied numerically. Predictions of both steady and transient flow properties from this model are validated with experiments conducted on a 1.32 m long cylindrical duct, with a cross-sectional diameter of 52 mm, rotating at speeds of upto 1050 RPM (Tip Speed = 145 m/s). Spanwise pressure distribution, duct velocity, temperature, hub forces and moments results from the numerical model showed good correlation with experiments. Considerable internal mass flow rate (~ 0.3 kg/s) was also observed. In the presence of a time-varying valve at the inlet, transient spanwise pressure variations showed periodic fluctuations in pressure which diminished once the valve was fully open. The quasi 1-D model was found to be a much faster computational tool than any conventional 3-D CFD solver to study spanwise flow inside rotor blades. The experiments revealed key information about pressure at the duct's outlet. It was observed that when the duct's inlet is closed, the duct's outlet pressure is less than its ambient value. The knowledge of these boundary conditions is essential in modeling flow through rotating ducts. For more accuracy, the current internal flow solver could be coupled with an external flow code to iteratively obtain boundary conditions at their interface.

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