Power Augmentation Research Articles

Some design guidelines to adapt a Darrieus vertical axis turbine for use in hydrokinetic applications

The use of vertical-axis turbines is raising interest in the field of hydropower production from rivers or water channels, where suitable mass flows are available, without the need of high water jumps or large construction sites. Although many optimization studies on vertical-axis turbines have been carried out for wind applications, lesser examples exist in the technical literature regarding hydrokinetic turbines. In the latter case, the best trade-off between power output and low structural stress is more dependent on the fluid dynamic loadings rather than the inertial loadings, due to the higher fluid density and lower rotation speed. The present work shows the results of an industrial study case application, in which the design of a traditional three-blade Darrieus rotor has been adapted for operating in water flows via hydrokinetic technology. Some specific design rules will be discussed, showing the different concepts adopted for the machine layout in order to achieve the best efficiency and performance. Multiple geometrical parameters of the rotor configuration were involved during the analysis: the number of rotor blades, i.e. two or three blades, the rotor’s shape, i.e. traditional H-shape or unconventional L-shape, and the use of power augmentation systems. The analysis of the numerical results was focused on the following output targets: maximum power coefficient, optimal tip speed ratio (TSR), rotor thrust, blade normal force and the upstream and downstream flow field influence. The outcome of the study shows how the best configuration differs from the common solutions for wind application. Moreover, a high power enhancement can be achieved while guaranteeing a good compromise in terms of structural loads.

Savonius wind turbines: A review of recent advances in design and performance enhancements

The energy crisis due to a rapid globalization and adverse effects of global warming has led to an increased need for the non-conventional sources of energy. In the recent times, significant research activities are carried out in the renewable energy field, mostly in solar and wind power generation. Wind turbines are categorised into vertical axis wind turbines (VAWT) and horizontal axis wind turbines (HAWT). Savonius rotor (S-type) is a type of VAWT and its function depends on the drag force. It has many advantages of easy installation, simplicity in design, good self-starting capability, low speeds operation and independency of direction of wind. Although, the negative torque produced on the returning blade leads to its low efficiency. Researchers have conducted several investigations to improve the functioning of Savonius rotor for satisfying large-scale energy demands. The parameters affecting the performance, such as, overlap ratio, aspect ratio, tip speed ratio and blade shapes, are improved by undergoing various designs. Several augmentation techniques, such as, end plates, shielding obstacle, guide box tunnel, deflecting plate, curtain plate, quarter blades and nozzles, have been used to enhance the performance of S-type VAWT. With the installation of these augmentation devices, the negative torque acting on the blades was reduced and the starting ability of the rotor was improved. These devices in turn help in increasing the power output as well as the torque coefficient of various rotor configurations. It has been reported in the literature that the coefficient of power of the conventional Savonius rotor lies in the span of 0.12 to 0.18. By using different methods for optimizing its design or installing the augmentation devices, the coefficient of performance can be improved to a value of 0.52. In this article various performance influencing parameters and the power augmentation techniques used for S-type VAWT have been studied and reported studies on these techniques have been reviewed. The article concludes with proposed directions for future research.

Forecasting of a boosted locomotive gas diesel engine parameters with one- and two-stage charging systems

Conversion of locomotive engines for operation on natural gas lowers considerably expenses for fuel and reduces exhaust emissions which makes it possible to omit large and expensive aftertreatment systems. The permanent need to raise the engine power requires a considerable increase of the boost pressure. This can be realized by using a high pressure turbocharger or a two-stage charging system. In the research, parameters of a high boosted D200 6-cylinder locomotive engine having D/S=200/280 mm are forecasted using a one-zone model developed in MADI. An analysis was carried out to explain why the 1st stage compressor of the two-stage charging system should be specially profiled to have its map tilted to the right. Calculations were performed for the gas diesel engine having a break mean effective pressure (BMEP) 2.7 MPa with one and two-stage charging systems. In both cases, close fuel efficiency was obtained, though for the two-stage charging system, the boost air pressure was higher. The engine with one turbocharger had no reserves for further power augmentation while the two-stage charging system enabled to increase the boost air pressure further. Therefore, parameters of the engine having a higher BMEP 3.2 MPa were calculated. In that case, not to exceed the peak combustion pressure, a retarded fuel injection was used which resulted in fuel efficiency drop by approximately 1.5%.

Characterization of aerodynamic performance of wind-lens turbine using high-fidelity CFD simulations

Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (Cp)is calculated by solving the URANS equations with the aid of the SST k–ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.

EEG-Based EMG Estimation of Shoulder Joint for the Power Augmentation System of Upper Limbs

Brain–Machine Interfaces (BMIs) have attracted much attention in recent decades, mainly for their applications involving severely disabled people. Recently, research has been directed at enhancing the ability of healthy people by connecting their brains to external devices. However, there are currently no successful research reports focused on robotic power augmentation using electroencephalography (EEG) signals for the shoulder joint. In this study, a method is proposed to estimate the shoulder’s electromyography (EMG) signals from EEG signals based on the concept of a virtual flexor–extensor muscle. In addition, the EMG signal of the deltoid muscle is used as the virtual EMG signal to establish the EMG estimation model and evaluate the experimental results. Thus, the shoulder’s power can be augmented by estimated virtual EMG signals for the people wearing an EMG-based power augmentation exoskeleton robot. The estimated EMG signal is expressed via a linear combination of the features of EEG signals extracted by Independent Component Analysis, Short-time Fourier Transform, and Principal Component Analysis. The proposed method was verified experimentally, and the average of the estimation correlation coefficient across different subjects was 0.78 (±0.037). These results demonstrate the feasibility and potential of using EEG signals to provide power augmentation through BMI technology.

A Novel Walking Speed Control Strategy for Power Augmentation Exoskeletons based on Neural Networks

This paper addresses a novel sensing technique to minimize the interaction force of walking speed transitions during the navigation of a coupled human-exoskeleton power augmentation system. The proposed technique is able to classify the intended walking speed based on Dual Reaction Force (DRF) Sensor. The human brain as a complex information processing device is quite difficult to be simulated, especially when considering the processing speed and the speed of sensed signals through the human nervous system throughout the human body. We developed the DRF sensors for preemptive identification of pilot intentions for walking speed transitions to augment the response of the exoskeleton to shadow pilot's movements. The Dynamic Threshold Neural Networks (DTNNs) is used to classify the input signals and make a decision on the transition of system's walking speed according to the pilot's intentions and walking speed limitation. The actions for walking speed transitions are simulated in MATLAB/Simulink, and Variable Admittance Controller (VAC) and applied. To show the efficiency of the proposed walking speed control strategy, comparison is conducted with ordinary VAC algorithm technique.

Performance and Low-Frequency Noise of 22-nm FDSOI Down to 4.2 K for Cryogenic Applications

This work presents the performance and low-frequency noise (LFN) of 22-nm fully-depleted silicon-on-insulator (FDSOI) CMOS technology. The experimental measurements and the analysis are performed as a function of temperature for the first time, focusing on cryogenic applications, down to 4.2 K. The back bias impact on device performance is evaluated. The results reveal that the threshold voltage tuning is found to be temperature independent, allowing extra drain current improvement. This is particularly interesting for short channel devices, whose drain current gain with temperature lowering is expected to be smaller in comparison with long channel MOSFETs. LFN is characterized by means of time-domain current sampling measurements. Moderate and strong inversion regimes are investigated. The carrier number with correlated mobility fluctuations model can well describe the 1/f noise behavior down to 4.2 K. The physical origin behind the drain current noise-to-signal power augmentation with temperature lowering could be mainly attributed to the normalized transconductance improvement.

Short-Term Effects of “Composite” Training on Strength, Jump, and Sprint Performance in Hurling Players

Byrne, PJ, Moody, JA, Cooper, S-M, Farrell, E, and Kinsella, S. Short-term effects of "composite training" on strength, jump, and sprint performance in hurling players. J Strength Cond Res 36(8): 2253-2261, 2022-The purpose of this study was to compare the short-term effects of "composite" training to sprint training on strength, jump, and sprint acceleration performance in hurling players. A randomized counterbalanced group design with baseline test, pretest and post-test measures was used. Twenty-five hurling players volunteered to participate and 21 completed the study. Subjects were divided into a "composite" (COMP group, n = 10) or a sprint training (SPRINT group, n = 11) group. Both groups trained twice per week for 7 weeks with the SPRINT group performing 6 repetitions of 20 m sprints and the COMP group completing 6 repetitions (1 repetition = 3 bounce drop jumps [BDJs] with a 20 m sprint after 15 seconds recovery). Significant differences existed pretraining to post-training for the COMP group for BDJ contact time (-7.25%; p = 0.05) and countermovement jump (CMJ) variables (height: 7.43%, p = 0.006; force: 5.24%, p = 0.05; power: 15.11%, p = 0.001). No significant differences were found between groups at baseline and for group by time interactions. Significant improvements were observed pretraining to post-training in both groups for the following: absolute 3 repetition maximum (3RM) back squat strength (12.73-17.62%, p = 0.01), 5 m (5.74-9.49%, p = 0.006-0.04), 10 m (4.27-5.59%, p = 0.007-0.02), and 20 m (3.35-3.98%, p = 0.003-0.01). In conclusion, "composite" training is effective in enhancing fast stretch-shortening cycle efficiency inducing CMJ force and power augmentation. However, "composite" and sprint training are effective training approaches for enhancing maximal strength and sprint performance in a time efficient manner in hurling players.

Integration of Municipal Air-Conditioning, Power, and Gas Supplies Using an LNG Cold Exergy-Assisted Kalina Cycle System

A Kalina cycle-based integration concept of municipal air-conditioning, electricity and gas is investigated thermodynamically, economically, and environmentally to reduce the carbon intensity of these supplies, with attention to hot climatic conditions. The proposed poly-generation system is driven by low-grade renewable or surplus heat, and utilizes waste exergy from liquefied natural gas vaporization for refrigeration and power augmentation. At nominal conditions (130 °C driving heat), approximately 561 and 151 kJ of refrigeration and useful power per kg of liquefied natural gas regasified are generated by the proposed system, respectively, at effective first-law and exergetic efficiencies of 33% and 35%, respectively. The Kalina sub-system condenser cryogenic heat rejection condition is found to triple the system useful electrical output compared with high ambient temperature condenser heat sinking conditions. Per million ton per annum of liquefied natural gas vaporization capacity, yearly net power savings of approximately 74 GWhe could be achieved compared to standard air-conditioning, electricity, and gas supply systems, resulting in 11.1 kton of natural gas saved and 30.4 kton of carbon dioxide-equivalent emissions avoided annually. The yearly net monetary savings would range from 0.9 to 4.7 million USD per million ton per annum of liquefied natural gas regasified at local subsidized and international electricity market prices, respectively, with corresponding payback periods of 1.7 and 2.5 years, respectively.

Investigation of the Possibilities to Improve Hydrodynamic Performances of Micro-Hydrokinetic Turbines

Horizontal axis turbines are commonly used for harnessing renewable hydrokinetic energy, contained in marine and river currents. In order to encourage the expansion of electricity generation using micro-hydrokinetic turbines, several design improvements are investigated. Firstly, optimization-based design of rotor blade is used to get as close as possible to the efficiency limit of 59.3% (known as Betz limit), that counts for bare turbine rotors, placed in the free flow. Additional diffuser elements are further added to examine the potential to overcome the theoretical efficiency limit by accelerating water at the axial direction. Various diffuser geometrical configurations are investigated using the computational fluid dynamics (CFD) to obtain insight into hydrodynamics of augmented micro-hydrokinetic turbines. Moreover, the turbines are compared from the energy conversion efficiency point of view. The highest maximum power coefficient increase of 81% is obtained with brimmed (flanged) diffuser. Diffusers with foil-shaped cross-sections have also been analyzed but power augmentation is not significantly greater than in the case of simple cross-section designs of the same dimensions. The power coefficients’ comparison indicate that considerable power augmentation is achievable using brimmed diffuser with higher value of length-to-diameter ratio. However, the impact of diffuser length increase on the power coefficient enhancement becomes weaker as the length-to-diameter ratio reaches a value of 1.

Exergy analysis of combined cycle power plant with carbon capture and utilization

ABSTRACT Generally, thermal power plants operate on hydrocarbon fuels and produce emissions consisting of carbon dioxide which is a major contributor to air pollution and global warming. The present study considers retrofitting an existing gas/steam combined cycle power plant arrangement to get carbon dioxide from gas turbine exhaust and convert it into methane to run additional gas turbine for power augmentation. Here exergy analysis of the considered combined cycle estimates the exergy efficiency and exergy destruction of major components. The study shows the comparative results for different components of power plant with and without carbon capture arrangement. The highest exergy destruction occurs in combustion chamber at 12.7 cycle pressure ratio, 1400 K turbine inlet temperature while it is minimum at 8.7 cycle pressure ratio and 1475 K turbine inlet temperature. The highest exergy efficiency of 96.66% was obtained for the gas turbine at 12.7 cycle pressure ratio and 1475 K turbine inlet temperature. These exergy estimations help in knowing the relative performance of different components of the cycle under consideration which can be used for the future development of such systems.

Aeroderivative gas turbine back-up capability with compressed air injection

The transition to more renewable energy sources of power generation is associated with grid instability and the need for backup power, due to their intermittency. This provides an opportunity for gas turbine engines, especially the aeroderivative (AD) types that generally have higher ramp rates than heavy-duty engines. Nonetheless, higher ramp rates are still necessary to meet more stringent grid requirements, with increased renewables subscription. The study examines ramp rate improvements and performance enhancement through compressed air injection at the back of the high-pressure compressor (HPC). Two configurations of AD engines are considered in the investigation. In-house gas turbine performance simulation software has been used to simulate the steady-state and transient operations for design and off-design performance. Compressed air injection in the study is facilitated by an assumed compressed air storage or an external compressor. The steady-state analysis for power augmentation shows that for the two-spool engine with fixed speed low-pressure compressor (LPC), a 16% increase in power is obtained with 8% of flow injection. The other engine that is intercooled and consists of a variable speed LPC with power turbine shows a 21% increase in power for the same injection amount. Above 8% injection, the HPC of both engines tends towards an adverse rise in pressure ratio. However, up to 15% of flow injection is allowed before the surge point. It is seen generally that the operating point of the LPC moves away from surge, while the opposite is the case for the HPC. For transient simulations focused on ramp rates, the better improvements are shown for the intercooled engine that runs at variable speed. This is a ramp rate improvement of 100% with air injection, while that of the other engine increases by 85%.

Electric Power and Heat Generation Expansion Planning

A short-term electric power and heat generation augmentation planning (EPHGAP) is portrayed and evaluated here. The objective of EPHGAP is to find out the most cost-effective and dependable expansion plan for meeting the forecasted electrical power demand and heat demand over a long-range horizon while fulfilling a large number of technical, cost-effective, reliability, and social constraints. The EPHGAP problem is a big-dimensional highly constrained mixed integer nonlinear programing (MINLP) problem. The general algebraic modeling system (GAMS) environment has been used to implement the proposed formulation, and the EPHGAP problem is solved by using Basic Open-source Nonlinear Mixed Integer (BONMIN) solver. An archetypal test system with existing thermal power plants, cascaded hydropower plants, cogeneration units, heat-only units and candidate cogeneration units, and cascaded hydro plants is considered to evaluate the proposed methodology. Simulation outcomes of the test system have been matched up to those acquired by differential evolution and particle swarm optimization. It has been observed from the comparison that the recommended BONMIN solver has the capability to bestow with superior quality solution.

Analysis and prediction of gas turbine performance with evaporative cooling processes by developing a stage stacking algorithm

Water injection in stationary gas turbines is effective strategy for power augmentation and gas turbine efficiency improvement, in particular, at high ambient temperatures. In this study, a developed method for simulation of wet compression processes is introduced. This method is followed by the droplet evaporation analysis, aero-thermodynamic stage-stacking model, and a map zooming technique for evaluation the unknown parameters in the generalized performance curves by using grey wolf optimization (GWO) algorithm. The validity of the proposed algorithm is assessed through the comparison of the results with two experimental studies. The operating results are calculated for five different cities and 18 gas turbines organized in three classes. Moreover, a sensitivity analysis on the main input parameters is investigated with the use of variable importance (VI) analysis by constructing and training an artificial neural network. The results show that the variation of the output parameters is highly sensitive to the ambient temperature, relative humidity, and turbine inlet temperature (TIT). Results demonstrate that saturated fogging plus 1% overspray leads to a relative increase of 24.84% and 6.70% in net power output and thermal efficiency, respectively, at the corresponding ambient condition. It is observed that 23.94% of the increase in the inlet mass flow rate in this cooling approach is due to the injected water directly, where the compressor operating point is matched at a point with a higher inlet mass flow rate comparing to dry condition.

Flow Simulations of Modified Diffuser Augmented Wind Turbine

In order for wind technology to compete with conventional sources of energy, in terms of energy production costs, researchers are working on different ways to increase the energy density in wind. Development of wind power augmentation system is one of the most promising concepts in this field. The main objective of this research is to propose a new diffuser design for Diffuser Augmented Wind Turbine (DAWT) by introducing air vents and vortex generators. This study also investigates the effect of wind velocity and air pressure on the proposed modified diffuser to develop a suitable diffuser for DAWT. The purpose of this modified diffuser is to create a low-pressure region in the centre of the diffuser to increase the inlet mass flow rate. Three modified designs were developed and were simulated using CFD techniques. Results showed an outstanding increment in wind speed, which is 8.56 m/s (2.14 times increment), over the 4 m/s initial wind speed in a modified diffuser (Model 3 Air vents with splitter). This modified diffuser is based on the parameters: rotor diameter (D) = 500 mm, diffuser length (L) = 1000 mm, diffuser open-angle (θ) = 12º, flange size = 221.73 mm and inner splitter with 14º open-angle (α).

Effect of a winglet on the Power Augmentation of Straight Bladed Darrieus Wind Turbine

There has been an increased interest in enhancing the relatively low power coefficient of the Vertical axis wind turbine (VAWTs) for wider applications. Winglets are an effective solution for improving the aerodynamic performance in the aerospace field, and this paper numerically studies the aerodynamic effect of adding a winglet on the blade of a VAWT. The Computational Fluid Dynamics (CFD) base model is verified by experimental data from the available literature. The present work compares the effect of a winglet on the turbine performance of a VAWT. As a result, the power performance of the turbine with the appended winglets increases. The winglet assists in maintaining the pressure between the two sides of the blades. And, thus, weakens the tip vortex and improves the aerodynamic efficiency of the turbine blade.

Gas turbine efficiency and ramp rate improvement through compressed air injection

With the transition to more use of renewable forms of energy in Europe, grid instability that is linked to the intermittency in power generation is a concern, and thus, the fast response of on-demand power systems like gas turbines has become more important. This study focuses on the injection of compressed air to facilitate the improvement in the ramp-up rate of a heavy-duty gas turbine. The steady-state analysis of compressed airflow injection at part-load and full load indicates power augmentation of up to 25%, without infringing on the surge margin. The surge margin is also seen to be more limiting at part-load with maximum closing of the variable inlet guide vane than at high load with a maximum opening. Nevertheless, the percentage increase in the thermal efficiency of the former is slightly greater for the same amount of airflow injection. Part-load operations above 75% of power show higher thermal efficiencies with airflow injection when compared with other load variation approaches. The quasi-dynamic simulations performed using constant mass flow method show that the heavy-duty gas turbine ramp-up rate can be improved by 10% on average, for every 2% of compressor outlet airflow injected during ramp-up irrespective of the starting load. It also shows that the limitation of the ramp-up rate improvement is dominated by the rear stages and at lower variable inlet guide vane openings. The turbine entry temperature is found to be another restrictive factor at a high injection rate of up to 10%. However, the 2% injection rate is shown to be the safest, also offering considerable performance enhancements. It was also found that the ramp-up rate with air injection from the minimum environmental load to full load amounted to lower total fuel consumption than the design case.

Improvement of a Flanged Diffuser Augmented Wind Turbine Performance by Modifying the Rotor Blade Aerodynamic Design

Shrouding of HAWT in a flanged diffuser is among techniques of wind power augmentation especially in urban areas. In this paper, a small scale of Flanged Diffuser Augmented Wind Turbine (FDAWT) was presented with flanges angle (?f) of 0°. The rotor fit for FDAWT was designed based on a modified blade element momentum theory, which adopts on developing the preliminary rotor blade geometry in terms of pitch angle. The modification of the blade pitch angle was based on the maximum wind speeds in the empty flanged diffuser at rotor position along the blade sections. The models of rotor and diffuser were fabricated and experimented in the wind tunnel. The experimental tests were conducted to calculate the power at a different wind velocity ranged 5 - 9 m/s. The performance tests were in terms of power coefficient, CP and torque coefficient, CQ as a function of the tip speed ratio as well as maximum power as a function of the wind velocity. The results show the rate of increase in the maximum power producing for the FDAWT with the modified rotor up to 291% more than what it is for the preliminary bare HAWT, while this increase was only 257% for FDAWT with the preliminary rotor.

Transcranial Direct Current Stimulation Effect on Virtual Hand Illusion.

Virtual reality (VR) is effectively used to evoke the mirror illusion, and transcranial direct current stimulation (tDCS) synergistically facilitates this illusion. This study investigated whether a mirror virtual hand illusion (MVHI) induced by an immersive, first-person-perspective, virtual mirror system could be modulated by tDCS of the primary motor cortex. Fourteen healthy adults (average age 21.86 years ±0.47, seven men and seven women) participated in this study, and they experienced VR with and without tDCS-the tDCS and sham conditions, each of which takes ∼30 minutes-on separate days to allow the washout of the tDCS effect. While experiencing VR, the movements of the virtual left hand reflected the flexion and extension of the real right hand. Subsequently, electroencephalogram was recorded, the magnitude of the proprioceptive shift was measured, and the participants provided responses to a questionnaire regarding hand ownership. A significant difference in the proprioceptive shift was observed between the tDCS and sham conditions. In addition, there was significant suppression of the mu power in Pz, and augmentation of the beta power in the Pz, P4, O1, and O2 channels. The difference in proprioceptive deviation between the two conditions showed significant negative correlation with mu suppression over the left frontal lobe in the tDCS condition. Finally, the question "I felt that the virtual hand was my own hand" received a significantly higher score under the tDCS condition. In short, applying tDCS over the motor cortex facilitates the MVHI by activating the attentional network over the parietal and frontal lobes such that the MVHI induces more proprioceptive drift, which suggests that the combination of VR and tDCS can enhance the immersive effect in VR. This result provides better support for the use of the MVHI paradigm in combination with tDCS for recovery from illnesses such as stroke.

Aerodynamic performance optimization of an airfoil-based airborne wind turbine using genetic algorithm

The present manuscript proposes an aerodynamically optimized airfoil-based-shell for performance enhancement of the buoyant airborne turbine system. An integrated code, based on a genetic algorithm, is developed to parametrize the asymmetric airfoil NACA-9415, analyse its aerodynamics and optimize the lift of the airfoil. The 3D steady-state analysis is performed on the optimized shell geometry with NREL-IV rotor using Reynolds Averaged Navier-Stokes (RANS) equation along with k−ωSST turbulence model. The performance of the airborne wind turbine with the optimized shell configuration is assessed in terms of aerodynamic coefficients including shell thrust coefficient, shell back pressure coefficient, turbine power coefficient and power augmentation ratio. The comparison of wind turbine performance with optimized and original NACA-9415 shell configuration demonstrates that shell optimization results in a maximum power coefficient of 1.25 and power augmentation ratio of 2.1 compared to the Betz limit.