This paper is the result of a master thesis project on helicopter rotor downwash effects using computational fluid dynamics (CFD). The work was performed at the department of Aerodynamics and Flight Mechanics at Saab AB, Linköping in 2008. It completes the author’s studies for a M.Sc degree in Applied Physics and Electrical Engineering at the Department of Electrical Engineering at the Linköping institute of technology (LiTH), Linköping, Sweden.   The aim of the project was to study the rotor downwash effects and its influence on the helicopter fuselage. To fulfil this purpose, several CFD calculations were carried out and the aerodynamic forces and moments resulting from the calculations were implemented in an existing simulation model, developed in-house at Saab. The original (existing) model was compared to the updated model by studying step responses in MATLAB, Simulink. For some step commands, the comparisions indicated that the updated model was more damped in yaw compared to the original model for the hovering helicopter. When the helicopter was trimmed for a steady turn, the states in the updated model diverged much faster than the states in the original model for any given step command.     In order to investigate the differences between the original helicopter model and the updated model from a controlling perspective, a linear quadratic (LQ) state feedback controller was synthesized to stabilize the vehicle in a steady turn. The LQ method was chosen as it is a modern design technique with good robustness and sensitivity properties and since it is easily implemented in MATLAB.  Before synthesising, a simplification of the helicopter model was made by reducing states and splitting them into lateral and longitudinal ones. Step responses from simulations with the original and the updated model were studied, showing an almost identical behavior.   It can be concluded that the aerodynamic coefficients obtained from the CFD calculations can be used for determining the aerodynamic characteristics of the helicopter. Some further validation is needed though, for example by comparing the results with flight test data. In order to build an aerodynamic data base that covers the whole flight envelop, additional CFD calculations are required.

Experimental research has been completed using a custom designed and built 4m diameter wind turbine in a university operated wind facility. The primary goals of turbine testing were to determine the power production of the turbine and to apply the particle image velocimetry (PIV) technique to produce flow visualization images and velocity vector maps near the tip of a blade. These tests were completed over a wide range of wind speeds and turbine blade rotational speeds. This testing was also designed to be a preliminary study of the potential for future research using the turbine apparatus and to outline it's limitations. The goals and results of other large scale turbine tests are also briefly discussed with a comparison outlining the unique aspects of the experiment outlined in this thesis. Power production tests were completed covering a range of mean wind speeds, 6.4 m/s to 11.1 m/s nominal, and rotational rates, 40 rpm to 220 rpm. This testing allowed the total power produced by the blades to be determined as a function of input wind speed, as traditionally found in power curves for commercial turbines. The coefficient of power, Cp, was determined as a function of the tip speed ratio which gave insight into the peak power production of the experimental turbine. It was found, as expected, that the largest power production occurred at the highest input wind speed, 11.1 m/s, and reached a mean value of 3080 W at a rotational rate of 220 rpm. Peak Cp was also found, as a function of the tip speed ratio, to approach 0.4 at the maximum measurable tip speed ratio of 8. Blade element momentum (BEM) theory was also implemented as an aerodynamic power and force prediction tool for the given turbine apparatus. Comparisons between the predictions and experimental results were made with a focus on the Cp power curve to verify the accuracy of the initial model. Although the initial predictions, based on lift and drag curves found in Abbot and Von Doenhoff (1959), were similar to experimental results at high tip speed ratios an extrapolation of the data given by Hoffman et al. (1996) was found to more closely match the experimental results over the full range of tip speed ratios. Finally PIV was used to produce flow visualization images and corresponding velocity maps of the chord-wise air flow over an area at a radius ratio of 0.9, near the tip of a blade. This technique provided insight into the flow over a blade at three different tip speed ratios, 4, 6 and 8, over a range of wind speeds and rotational rates. A discussion of the unique aspects and challenges encountered using the PIV technique is presented including: measuring an unbounded external flow on a rotating object and the turbulence in the free stream affecting the uniform seeding and stability of the flow.

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This thesis aims to investigate the performance of a horizontal water turbine in ocean current. The design of the water turbine is based on the Blade Element Momentum theory to begin with. As the water current flows past a single turbine, the water inflow velocity and the rotational speed are the parameters to be investigated. Furthermore, the interaction of more than two turbines due to the relative distance is also discussed. The relative distance encompasses both the front and the back. The results show that the water inflow velocity and the turbine rotational speed influence the performance of the turbine. When two turbines function simultaneously, the flow field is different from the one of a single turbine and thus influences the performance of the other turbines in the vicinity. Lastly, the site arrangement of three turbines is discussed, and it is revealed that a proper arrangement can enhance the performance of the turbines.

Beef fajitas have become a popular food item, but the supply of traditional muscles is insufficient to meet the growing demand. There is a need for alternative muscles that have similar eating characteristics to those currently marketed as beef fajitas. Four different treatments - papain (P), blade tenderization (B), papain + blade tenderization (P+B), and control (C) - were applied to sixty USDA Choice M. diaphragma pars costalis, M. transversus abdominis, M. obliquus abdominis internus, M. rhomboideus, M. trapezius, M. latissimus, and M. serratus ventralis. Muscles were cut into sections and frozen at -10ºC for evaluation by a trained sensory panel, consumer panel, and Warner-Bratzler shear force (WBSF) measurements. Trained panelists found that regardless of muscle, the addition of papain improved palatability scores. In general, treatment tended not to affect the palatability scores of the M. diaphragma pars costalis and M. serratus ventralis, which tended to receive higher scores in comparison to the other muscles. In general, the control and blade tenderized M. trapezius received the lowest trained and consumer panel palatability scores and had the highest WBSF values (P < 0.05). Regardless of muscle (except for M. diaphragma pars costalis and M. serratus ventralis), P and P+B treatments reduced WBSF values (P < 0.05). Consumers (n=81) gave the M. transversus abdominis, M. serratus ventralis, and M. latissimus similar (P > 0.05) tenderness ratings when the P treatment was applied. Consumers tended to prefer the flavor and tenderness of beef fajita strips that were treated with P and P+B and indicated a preference to purchase muscles with these treatments. Consumers were willing to purchase M. serratus ventralis treated with P+B and M. latissimus treated with P the majority of the time. Papain improved the eating quality of the muscles studied. The M. latissimus and M. serratus ventralis when treated with papain alone or in combination with blade tenderization, performed well enough to be considered as alternatives for traditional beef fajitas.

Renewable energy is a serious alternative to deliver the energy needs of an increasing world population and improve economic activity. Wind energy provides better environmental and economic benefits in comparison with the other renewable energy sources. Wind energy is capable of providing 72 TW (TW = 10^12 W) of electric power, which is approximately four and half times the world energy consumption of 15.8 TW as reported in 2006. Since power output extracted from wind turbines is proportional to the square of the blade length and the cube of the wind speed, wind turbine size has grown rapidly in the last two decades to match the increase in power output. As the blade length increases, so does its weight opening up design possibilities to introduce hybrid glass and carbon fiber composite materials as lightweight structural load bearing alternatives. Herein, we investigate the feasibility of introducing modular composite tubulars as well as hybrid sandwich composite skins in the next generation blades. After selecting a target energy output, 8 MW with 80 m blade, airfoil geometry and the layup for the skin as well as internal reinforcements are proposed. They are incorporated into the computational blade via linear shell elements for the skin, and linear beam elements for the composite tubulars to assess the relationship between weight reduction and structural performance. Computational simulations are undertaken to understand the static and dynamic regimes; specifically, displacements, stresses, and vibration modes. The results showed that the composite layers did not exhibit any damage. However, in the balsa core of the sandwich skin, the von Mises stress exceeded its allowable at wind speeds ranging from 11.0 m/sec to 12.6 m/sec. In the blades with composite tubular reinforcement, two different types of damage are observed: a. Stress concentrations at the tubular-skin attachments, and b. Highest von Mises stress caused by the flapping bending moment. The vibration studies revealed a strong coupling mode, bending and twist, at the higher natural frequencies of the blade with tubular truss configuration. The weight saving measures in developing lighter blades in this study did not detract from the blades structural response for the selected load cases.

During the three decades, the torsional impact on turbine-generator sets due to power system disturbances has been extensively discussed in many research works. However, most of them are focused on the fatigue damage of turbine shafts due to large-signal disturbances. For example, network faults occur. Obviously, the torsional effect subject to small-signal disturbances has not received much attention. In fact, although the small disturbances would not immediately damage the turbine mechanism, the cumulative long-term damaging effects may not be negligible under certain circumstances. Many operating conditions in power systems may lead to small disturbances on blades; for examples, shedding loads, switching transmission line, resetting control system parameters, and harmonics etc. Nevertheless, others only cause short-term or transient non-resonant disturbances occasionally except the power system subharmonics which could results in electro-mechanical resonance. Therefore, two types of subharmonics in power systems are proposed so as to investigate the toque impact and long-term fatigue life expenditure in turbine shafts and blades. Firstly, from the steady-state disturbance viewpoint, the long-term cumulative fatigue estimation based on the three-year project of the GE Co. shows that there are potential damages for both the shafts and the blades of the nearby generators caused by the subharmonic excitations of the HVDC link. The fatigue life sensitivity works are also carried out to provide the recommendations for the safety operation. The optimal damper type and disposition scheme for depressing the resonant torque and prolonging the turbine lifetime is consequently motivated, which is based on participation factor of linear systems with the electromechanical analogy. The effectiveness of this scheme on suppressing vibration torque arising from network faults is also satisfying. In addition, the authors propose the new electromechanical supersynchronous resonance phenomenon for the turbine-generators near the inverter station owing to asymmetric line faults near the rectifier station. Secondly, the dramatic real and reactive power consumption during the melting period of an electrical arc furnace load. The voltage flicker pollution is mainly caused by the reactive power fluctuation while the stochastic subsynchronous oscillation in turbine mechanism is excited by the electromagnetic torque of the subsynchronous frequency which is induced by the real power fluctuation. Such a small stress imposed on the low-pressure long turbine blade combined with its evitable corrosive environment contributing to the corrosion fatigue effect. Although the voltage flicker severity at the point of common coupling is still within the limit, the blade may have been damaged from the long-term corrosion fatigue life expenditure estimation. In other words, the conventional voltage flicker limit established to make human-eye comfortable might not protect the blade from damaging risk. The long-term influence resulted from the electric arc furnace loads cannot always be neglected. It is necessary to take care of the blade material intensity and operating environment. If there is the potential of blade damage, one has to strengthen the output capacity at the power plant or separate the peak load durations among the steel plants to limit the over-fluctuation real power of the generator.

This thesis investigates the flow field of a twin-engine, medium lift utility helicopter numerically. The effects of the exhaust hot gases emerging from the engines are accounted for in the numerical study. The commercial computational fluid dynamics (CFD) software ANSYS Fluent is employed for the computations. While the effects of engines are included in the computations through simple inlet and outlet boundary conditions, the main and tail rotors are simulated by the Virtual Blade Model in a time-averaged fashion. Forward flight at four different advance ratios and hover in ground effect are studied. The temperature distribution around the tail boom is compared to available flight test data. Good agreement with the flight test data is observed.

In this thesis analysis and design of helicopter rotor blades were discussed for reduced vibrational level. For this purpose an optimization procedure was developed which involves coupling of the comprehensive rotorcraft analysis tool CAMRAD JA and the gradient based optimization algorithm. The main goal was to achieve favorable blade structural dynamics characteristics that would lead to reduction in vibrational level. For this purpose blade stiffness and mass distributions were considered as the design variables. In order to avoid likely occurrences of unrealistic results, the analyses were subjected to constraints which were sensitive to the design variables. The optimization procedure was applied on two isolated rotor blades and a full helicopter with main rotor, tail rotor and fuselage by using natural frequency separation and hub load minimization respectively. While the former approach relied on the blade natural frequencies, the latter approach involved higher harmonic aerodynamic and blade motion calculations. For both approaches, the improvement in vibration characteristics and blade mass and stiffness distributions of the initial design and the design after optimization analyses were compared and discussed.

Abstract Maintenance makes machine life long more and gets no loss about a chain reaction on part broken. Repair a part that has high complex and is important. It need engineer experience to decide its maintenance process plan. For turbine blade maintenance style that has various type and a small quantity. Different broken feature have different maintenance process in the maintenance process planning stage. This thesis creates a system for this property maintenance on the process planning system on the Maintenance of turbine blades. Analyzing blade broken feature and classifying the feature to bring up a case-based reasoning and fuzzy set operation that usually see in expert systems. It uses case-based databases to save engineer experiences and analysis to decide critical maintenance process factors. The critical factors can help find out similarity case and modulate a newer case. It needs to create a proto-type system for these purposes. The first, classifying turbine blades broken feature and coding the repair process for different maintenances. The second, using fuzzy set language to determine case¡¦s similarity and finding out algorithm. Integrating product data management system and the system. The research uses a company as case study to test and verify the proto-type system.