Axial Impulse Research Articles

Characterization of loss, temperature, and stress on partial admission axial impulse turbines with liquid jet impingement cooling

The turbines for underwater applications can use abundant water as the cooling medium. However, the use of liquid water is associated with the multi-phase and multi-physics problems and presents additional losses. This paper proposes a numerical coupling method and corresponding loss breakdown approach to analyze the performance of this particular turbine cooling problem at different water mass flow rates. The results show that the cooling water induces additional loss, while the influence of the resulted structural deformation on turbine efficiency is comparatively small. Through numerical loss breakdown, it is found that the exit kinetic energy loss is significantly decreased, but other losses are increased correspondingly due to the cooling water. By examining the turbine stress and temperature distribution, the small water mass flow rate of 0.02 kg/s is sufficient to avoid damage to the disc, however, additional cooling is necessary to minimize the plastic region at the turbine blades. The suitable loss model for the turbine with cooling water is established and a relative difference less than 3 % is attained by comparing mean-line and numerical results. This work provides new insight into the analysis method and characteristics of the partial admission axial turbine with cooling water.

Fluid–Thermal–Structural Analysis of Partial Admission Axial Impulse Turbines With Liquid Jet Impingement Cooling

Abstract Increasing turbine inlet temperature is beneficial to enhance turbine performance. However, this also results in stringent cooling requirements. Unlike turbines in air cycle machines, the partial admission axial impulse turbines for underwater vehicles can utilize the abundant seawater as the cooling medium. In addition, the short blades cannot accommodate the complex cooling channels used in aero-engines, and the alternative way is jet impingement liquid cooling. This paper proposes a fluid–thermal–structural coupling method to investigate the performance of partial admission axial impulse turbines with water-cooling on the rotating wheel front surface. The volume of fluid multiphase model is employed to study the transient gas–liquid interaction, while the Lee model is chosen to model the heat and mass transfer during phase change. Also, a two-way weakly coupling method among fluid, thermal, and structure is utilized to account for fluid–structure interaction. The results show that the temperature distribution at the turbine wheel drops significantly with the jet impingement liquid cooling. The turbine efficiency is also reduced by 3.38% due to the mixing of cooling medium and gas. From stress analysis, the use of water-cooling can minimize turbine damage and ensure stable turbine operation. This study provides insight into the cooling method for partial admission axial impulse turbines for the underwater vehicle.

Enhancing the efficiency of an axial impulse turbine with a diffuser

In oscillating water column wave energy converters, the aerodynamic losses caused by flow misalignment between the rotor outlet and the outlet guide vane of self-rectifying impulse turbines are a significant design problem. The symmetrical positioning of guiding vanes on both sides of the rotor is the reason for it. In comparison to the equivalent Wells turbine, the efficiency of impulse turbines is lower because of these losses in the outlet guide vane. This paper presents a strategy to develop animproved design of an axial impulse turbine to reduce the losses in the outlet guide vane along with the residual kinetic energy loss by integrating a diffuser between the rotor and guide vanes. The proposed model was investigated numerically using RANS simulations. Multiple diffuser geometries were tested against the reference turbine for comparison of the performance characteristics. The results support the hypothesis behind the proposed design. The performance was compared extensively with the reference case in terms of the dimensionless loss coefficients for a better insight into the contribution of all the turbine sectors. The current work shows a possible design path for the performance improvement of the turbine. Results also support the fact that the guide vanes need to beredesigned for obtaining maximizing efficiency with the proposed design. The losses in the outlet guide vane were reduced by approximately 50% with an overall efficiency rise of around 2%.

Investigate air turbines performance for power generation by tidal waves in the river: A review

The phenomenon of climate change resulting from the increase of global warming has become one of the main problems facing the world. Where researchers and specialists have worked for many years to find a solution that reduces this phenomenon and limits its risks. Clean energy is likely an alternative to fossil fuel sources, which are the main source of global warming. One of the clean energy sources is ocean wave energy, which is a huge and untapped energy source, despite the possibility of extracting large amounts of energy from waves. This paper focuses on the study of deep-sea turbines and their results. A study was conducted on the capture chamber. The turbines are driven and generate electricity by using a wave energy harvesting system (oscillating water column). Reaction turbines (impulse and Wells turbines) are tested and evaluated for performance in an oscillating water column system. Reaction turbines have a narrow operating range, and higher peak efficiencies. In contrast, turbines that have a greater operating range and lower peak efficiency are impulse turbines. Wells stator turbine has the highest efficiency while a variable pitch axial impulse turbine has the widest operating range. Better efficiency possessed by turbines with optimized geometry than other turbines.

Application of integrated wave-to-wire modelling for the preliminary design of oscillating water column systems for installations in moderate wave climates

Oscillating water column (OWC) devices are the technical solution more favourably considered for a significant future exploitation of the energy potential of sea waves. While theoretically quite simple, these systems are indeed rather complex in terms of correct tuning between the caisson and turbine. Recent studies showed that only a holistic approach, also including turbine control, is the way of effectively performing their precise design.To this end, the research presents the application of an analytical wave-to-wire model of an OWC device for the preliminary optimisation of these systems for a small installation in a moderate wave climate in the Mediterranean Sea. More specifically, scatter matrices were determined for imposing the wave states of a selected location positioned in Tuscany (Italy). Regarding previous similar studies, a novel joint optimisation of the caisson and controlled turbine is proposed for the specific site. Either monoplane isolated Wells turbines and axial impulse turbines were analysed. The operating curves, performance parameters, and attended annual energy harvesting were calculated, providing an interesting overview of the functioning of the system. The optimised devices with the Wells and impulse turbomachines convert 36.71 and 42.17 MWh/year operating with a global efficiency of 6.82% and 7.84%, respectively.

Influence of rotator cuff preload on fracture configuration in proximal humerus fractures: a proof of concept for fracture simulation

IntroductionIn regard of surgical training, the reproducible simulation of life-like proximal humerus fractures in human cadaveric specimens is desirable. The aim of the present study was to develop a technique that allows simulation of realistic proximal humerus fractures and to analyse the influence of rotator cuff preload on the generated lesions in regards of fracture configuration.Materials and methodsTen cadaveric specimens (6 left, 4 right) were fractured using a custom-made drop-test bench, in two groups. Five specimens were fractured without rotator cuff preload, while the other five were fractured with the tendons of the rotator cuff preloaded with 2 kg each. The humeral shaft and the shortened scapula were potted. The humerus was positioned at 90° of abduction and 10° of internal rotation to simulate a fall on the elevated arm. In two specimens of each group, the emergence of the fractures was documented with high-speed video imaging. Pre-fracture radiographs were taken to evaluate the deltoid-tuberosity index as a measure of bone density. Post-fracture X-rays and CT scans were performed to define the exact fracture configurations. Neer’s classification was used to analyse the fractures.ResultsIn all ten cadaveric specimens life-like proximal humerus fractures were achieved. Two III-part and three IV-part fractures resulted in each group. The preloading of the rotator cuff muscles had no further influence on the fracture configuration. High-speed videos of the fracture simulation revealed identical fracture mechanisms for both groups. We observed a two-step fracture mechanism, with initial impaction of the head segment against the glenoid followed by fracturing of the head and the tuberosities and then with further impaction of the shaft against the acromion, which lead to separation of the tuberosities.ConclusionA high energetic axial impulse can reliably induce realistic proximal humerus fractures in cadaveric specimens. The preload of the rotator cuff muscles had no influence on initial fracture configuration. Therefore, fracture simulation in the proximal humerus is less elaborate. Using the presented technique, pre-fractured specimens are available for real-life surgical education.Level of EvidenceIII.

Development of a 10 kW class axial impulse single stage turboexpander for a micro-CHP ORC unit

Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly.

Aerodynamic design and experimental validation of high pressure ratio partial admission axial impulse turbines for unmanned underwater vehicles

High pressure ratio partial admission axial impulse turbines are typically employed for underwater vehicles due to small mass flow rate and machining constraints. However, little work has been focused on the generic design methodology for high pressure ratio partial admission axial impulse turbines. The experimental results and empirical correlations are mostly established upon low pressure ratio axial turbines. In this paper, the meanline turbine design method is first documented together with the performance prediction method at off-design points. The numerical loss breakdown method is then described to thoroughly verify empirical correlations. Both the meanline and numerical methods are thoroughly validated against experimental results and the difference among meanline, numerical and experimental results is less than 10%. A case study is then performed and a 13 kW partial admission axial impulse turbine is designed. The suitability of empirical correlations is confirmed by comparing the losses between the meanline and numerical methods, and the difference less than 5% at design and off-design points is attained. This paper provides the insight into the design methodology for high pressure ratio partial admission axial impulse turbines.

Optimized geometry design of a radial impulse turbine for OWC wave energy converters

Opposite to other types of turbines for OWC wave energy converters, like the axial impulse or the Wells turbine, there is scarce information about radial impulse turbines. The interest in radial impulse turbine for wave energy is low because the available research on it shows lower efficiencies than the competitors. On the other hand, radial turbines present several advantageous features that make it a worthy option if the efficiency is improved. The purpose of the present work is to propose a new geometry, not focused on improving the rotor efficiency, but on reducing losses downstream of the rotor. This new design, taking previous geometries as a reference, was based on the classical 2-D angle computations optimizing the flow and blade angles for both inflow and outflow modes. After setting a balanced agreement between both modes, a numerical model with the new design was mounted on ANSYS Workbench which has allowed to speed up the whole process by using the specific tools set for turbomachines. Taking advantage of the simulation speed provided by the use of this model. A solidity optimization process was performed out on the new geometry to decide the required number of blades and vanes of the proposed turbine. Once, the turbine was well-defined, it has been compared concerning the previous turbine under both, steady and non-steady flow. The improvement has been remarkable, reaching a 10 % in steady efficiency and 6.7 % in non-steady efficiency with respect to the previous geometries.

Oscillating Water Column Wave Energy Converter for Low Wave Height Conditions

For continuous and uninterrupted extraction of energy from marine wave motion, majority of wave energy extraction systems employ bi-directional turbines. The aerodynamic loss due to symmetrical placement of guide vanes causes a major loss in power output of the system. To optimize this problem, researchers have developed and tested a variety of oscillating water column air turbines. Most commonly used are the axial turbines because of their simplicity and operational ease. The present work focuses upon design of an oscillating water column energy extraction system based on uni-directional axial impulse turbine with a novel rectifying system arrangement which primarily focuses to minimize the losses due to downstream guide vanes and in turn shoot up the power output for low wave height conditions. A numerical model was developed and investigated using RANS equations and k-omega SST turbulence model. The results obtained portrays that the proposed flap based bi-directional impulse system is operationally viable and produces substantially greater power output in comparison to conventional bi-directional and uni-directional turbine systems under low wave height conditions. A hybrid choking scheme was followed which resulted in additional power output. Results show that full choking of the idle turbine is ensured during the inhalation cycle, which was not possible in existing models. During the exhalation cycle, additional power output was also obtained from the secondary turbine i.e., front end turbine during exhalation cycle. The proposed system generates maximum total power output at around flow coefficient of 1.

Coupled CAD-CFD automated optimization for leading and trailing edge of an axial impulse turbine blade

A bidirectional impulse turbine with fixed guide vanes is used in an oscillating water column to extract wave energy. The turbine suffers from low aerodynamic efficiency, and it is required to improve performance. In the present study, coupled CAD-CFD automated optimization of the blade leading and trailing edge ratio was performed to maximize the efficiency. The design points were generated using a central composite design sampling technique and response surface optimization method estimated the optimum design. The optimization pipeline was automated using the Ansys Design Exploration module. Ansys Turbo Grid was used for generating structured hexahedral elements in the computational domain, and the problem was solved in Ansys CFX® v16.2. The results showed that the modified leading and trailing edge enhanced the performance compared to the reference blade by minimizing the pressure drop. The optimized design improved the relative peak efficiency and torque by 3.4% and 2% respectively. Additionally, a detailed flow analysis has been reported in this paper.

Inducing pilon fractures in human cadaveric specimens depending on the injury mechanism: a fracture simulation.

Operative management of pilon fractures, especially high-energy compression injuries, is a challenge. Operative education is of vital importance to handle these entities. Not rarely, it is cut by economics and staff shortage. As public awareness toward operative competence rises, surgical cadaver courses that provide pre-fractured specimens can improve realism of teaching scenarios. The aim of this study is to introduce a realistic pilon fracture simulation setup regarding the injury mechanism. 8 cadaveric specimens (two left, six right) were fixed onto a custom drop-test bench in dorsiflexion (20°) and light supination (10°). The proximal part of the lower leg was potted, and the specimen was exposed to a high energetic impulse via an axial impactor. CT imaging was performed after fracture simulation to detect the exact fracture patterns and to classify the achieved fractures by two independent trauma surgeons. (AO/OTA recommendations and the Rüedi/Allgöwer). All cadaveric specimens could be successfully fractured: 6 (75%) were identified as a 43-C fracture and 2 (25%) as 43-B fracture type. Regardless of the identical mechanism two different kinds of fracture types were reported. In five cases (62.5%), the fibula was also fractured and in three specimens, a talus fracture was described. There was no statistically significant correlation found regarding Hounsfield Units (HU) and age as well as HU and required kinetic energy. A high energetic axial impulse on a fixed ankle specimen in light dorsiflexion (20°) and supination (10°) induced by a custom-made drop-test bench can successfully simulate realistic pilon fractures in cadaveric specimens with intact soft tissue envelope. Although six out of eight fractures (75%) were classified as a 43-C fracture and despite putting a lot of effort into the mechanical setup, we could not achieve an absolute level of precision. Therefore, we suggest that the injury mechanism is most likely a combination of axial loading, shear and rotation. III.

Customized ORC micro turbo-expanders - From 1D design to modular construction kit and prospects of additive manufacturing

Due to the various ORC applications, it is not expedient to design and build one standard turbogenerator. Therefore, authors developed a flexible “micro-turbine-generator-construction-kit (MTG-c-kit)” by means of which a customized turbogenerator can be made for any required power output between 1 and 200 kW, for a wide range of working fluids and boundary conditions – quickly, cost effectively and with high expander efficiency. The architecture and main features of this kit are briefly introduced.However, more focus is put on the developed 1D turbine design tool. It allows to quickly design and optimize a single stage turbine for any fluid and boundary conditions. The implemented models are presented on two specific design examples - an axial impulse and a radial inflow cantilever turbine. Also, the experimental results of the two micro turbines designed and built according to this approach, are presented and discussed.Focusing to further accelerate and cheapen the customized micro-turbogenerators for low temperature applications, we provide an outlook of possibilities of additive manufacturing methods like 3D printing of turbine nozzles and rotors. These new possibilities provide potential to improve the competiveness of small-scale ORC. A simple air turbine design with plastic and metal components has been manufactured and tested.

Fast Design Procedure for Turboexpanders in Pressure Energy Recovery Applications

Sustainable development can no longer neglect the growth of those technologies that look at the recovery of any energy waste in industrial processes. For example, in almost every industrial plant it happens that pressure energy is wasted in throttling devices for pressure and flow control needs. Clearly, the recovery of this wasted energy can be considered as an opportunity to reach not only a higher plant energy efficiency, but also the reduction of the plant Operating Expenditures (OpEx). In recent years, it is getting common to replace throttling valves with turbine-based systems (tuboexpander) thus getting both the pressure control and the energy recovery, for instance, producing electricity. However, the wide range of possible operating conditions, technical requirements and design constrains determine highly customized constructions of these turboexpanders. Furthermore, manufacturers are interested in tools enabling them to rapidly get the design of their products. For these reasons, in this work we propose an optimization design procedure, which is able to rapidly come to the design of the turboexpander taking into account all the fluid dynamic and technical requirements, considering the already obtained achievements of the scientific community in terms of theory, experiments and numeric. In order to validate the proposed methodology, the case of a single stage axial impulse turbine is considered. However, the methodology extension to other turbomachines is straightforward. Specifically, the design requirements were expressed in terms of maximum allowable expansion ratio and flow coefficient, while achieving at least a minimum assigned value of the turbine loading factor. Actually, it is an iterative procedure, carried out up to convergence, made of the following steps: (i) the different loss coefficients in the turbine are set-up in order to estimate its main geometric parameters by means of a one dimensional (1D) study; (ii) the 2D blade profiles are designed by means of an optimization algorithm based on a “viscous/inviscid interaction” technique; (iii) 3D Computational Fluid Dynamic (CFD) simulations are then carried out and the loss coefficients are computed and updated. Regarding the CFD simulations, a preliminary model assessment has been performed against a reference case, chosen in the literature. The above-mentioned procedure is implemented in such a way to speed up the convergence, coupling analytical integral models of the 1D/2D approach with accurate local solutions of the finite-volume 3D approach. The method is shown to be able to achieve consistent results, allowing the determination of a turbine design respectful of the requirements more than doubling the minimum required loading factor.

Experimental study of a small scale bi-directional axial impulse turbine for acoustic-to-mechanical power conversion

Abstract Axial impulse turbines have been utilized for oscillating water column wave-energy conversion because of their wide operating range without stalling point. Previous studies in the oscillating-flow environment gave no information on the performance of these turbines at high frequencies. This study extends the use of these turbines to conditions close to those encountered in thermoacoustic power generators, which require the turbine to operate at a large frequency in a closed duct. The use of bi-directional turbines as acoustic-to-mechanical power converters brings several advantages, such as their low acoustic impedance, in comparison with linear alternators, which facilitates integration with thermoacoustic engines. In the study, a variable-frequency test rig is set up using atmospheric air. Then, the performance of the bi-directional impulse turbine is studied at different rotor inlet/exit angle, rotor space-to-chord ratio, stator space-to-chord ratio, stator exit angle, and tip clearance. The dependence of the conversion efficiency on flow coefficient is reported over a set of constant input gas parcel velocities. The study also introduces an impedance segment to simulate the turbine on Delta-EC. The peak efficiency of the improved case is found to be 35.2% at a flow coefficient of 0.22, resulting an improvement of 38% over the reference case.

Aerodynamic design of an axial impulse turbine for the high-temperature organic Rankine cycle

This work presents the aerodynamic design of an 80 kW axial impulse turbine with siloxane MM as working fluid for high-temperature organic Rankine cycle (ORC) applications. Based on the conventional turbine design method, the 1D preliminary design and 3D numerical simulations under both design and off-design conditions are conducted. The numerical results agree well with the preliminary design. The total-to-total isentropic efficiency of the proposed turbine reaches 77.46% with the pressure ratio of 6.54 and rotational speed of 15000 rpm. It can remain a high level in a wide range of operating conditions, especially at high pressure ratios and low rotational speeds. By comparing the maximum decrease value of turbine efficiency depending on the relative tip clearance, the axial impulse turbine shows less sensitivity to the tip clearance than the conventional turbine. The appropriate cascade solidities for the stator and rotor are both higher than the recommended ranges for the conventional turbine, which provide the reference for the further design. Although the axial impulse turbine exhibits slightly lower efficiency than the other ORC turbines in the research, it features great advantages of low cost and wide application which allow the assessment for ORC practical applications.

Experimental and numerical studies on an OWC axial-flow impulse turbine in reciprocating air flows

In this study, an experimental facility and a transient numerical model are established to predict the complicated unsteady behaviors of oscillating water column air turbines under reciprocating air-flow conditions, which are closer to the actual sea states. There are a total of 256 cases in the experimental test. Three starting modes for the axial impulse turbine in symmetrical reciprocating air flows are identified, and over 93% of the cases are found to be self-starting cases. The peak cycle-averaged turbine efficiency is 0.53, which is larger than that observed in the steady-state tests. Compared to the efficiencies derived from the steady-state tests, the turbine has the possibility to achieve a better performance in the reciprocating air flows even under the same pneumatic power input. The numerical model is compared and validated by the experimental results. Effects of constant load on turbine performance are investigated numerically. An irregular air-flow profile based on the local sea-state is generated. The turbine self-starting processes under various moments of inertia are simulated numerically, and the angular velocities, torque outputs and the pneumatic powers are predicted and compared.

Numerical Analysis of the Influence of Design Parameters on the Efficiency of an OWC Axial Impulse Turbine for Wave Energy Conversion

Oscillating water column (OWC) axial impulse turbines permit the conversion of wave energy into electrical power. Unlike other hydropower units with a mature and well established technology, such turbines have been recently developed, there are still few prototypes operating and therefore there is a large space for optimizing its design. Many recent studies focus on the improvement of the efficiency and transient characteristics by means of experimentation and also simulation techniques. In the present paper we use a 3D numerical simulation model (computational fluid dynamics model with ANSYS-Fluent 18) to analyze the influence of different geometrical parameters on the efficiency of the turbine, which have been less discussed yet. A reference configuration case has been used to validate our simulation model by comparing it with previous experimental results. Then, parametric variations in the guide vane number and type, gaps between the rotating and stationary part and hub to tip ratio have been introduced in the model to discuss the influence of these effects. It is found that some of these parameters have an important influence on the efficiency of the turbine and therefore, the results presented in this paper can help to optimize future designs of OWC impulse turbines.

Performance analysis of low speed axial impulse turbine using two type nozzles for small-scale organic Rankine cycle

Expander is one of the core components in organic Rankine cycle (ORC). High rotating speed and limited working range are the key limitations on using turbine expander in small-scale ORC system. In this work, an axial turbine, consisting of 6 nozzles and 36 blades with mean diameter of 160 mm, is designed with partially admitted method to evaluate the feasibility of reducing rotating speed for small mass flow conditions and extending working range with R245fa used as working fluid. The results from 3D simulation show reasonable performance in design and off-design conditions. In design condition, the mass flow rate, turbine power output and turbine efficiency using Laval nozzle are 1.035 kg/s, 17.0 kW and 54.1%, higher than using convergent nozzle. However, the performance using convergent nozzle is better than using Laval nozzle when total mass flow is lower than 0.6 kg/s. Furthermore, reducing the number of nozzles can effectively increase power output of turbine and thermal efficiency of ORC for small mass flow conditions. With the designed turbine using 6 Laval nozzles and rotating at 10,000 RPM, the maximum net power output and thermal efficiency of bottoming ORC are 18.3 kW and 7.8%, respectively.

초임계 이산화탄소 발전을 위한 충동형 축류 터빈 개발

초임계 이산화탄소 발전을 위한 충동형 축류 터빈 개발