Low Turbine Research Articles

Performance Analysis of the Vortex Cuttings Cleaner: Turbine Hydraulic Drive and Cuttings Transport in Wellbore Annulus

Summary In the process of directional and horizontal well drilling, cuttings tend to settle and form a bed at the low side of the annulus due to gravity, which decreases the drilling rate and even causes accidents in severe cases. This paper analyzes the performance of a new tool, the vortex cuttings cleaner, which can be effective without rotation of the drillpipe. Based on the computational fluid dynamics (CFD) approach, together with the discrete phase, Euler, and dynamic mesh models, the vortex cuttings cleaner is investigated with respect to the turbine torque, turbine velocity, pressure drop, and cuttings transport in the annulus. The working mechanism of the vortex cuttings cleaner is clarified. Finally, field tests are conducted on the tool to evaluate its application in terms of service life, wellbore friction, and rate of penetration (ROP). The results show that the turbine can rotate continuously under hydraulic drive. The turbine torque/velocity and the tool’s pressure drop increase with increasing displacement. The cuttings transport in the annulus is jointly affected by factors such as turbine velocity, fluid velocity, and particle size. A too low or high turbine velocity is unfavorable for cuttings transport. Through the analysis of the number of particles and particle concentration, the optimal velocity is determined to be 125 rev/min. The swirling flow intensity in the annulus flow field increases with the increase in turbine velocity. Field applications suggest a service life longer than 200 hours, a notable decrease in wellbore friction, and an average increase in ROP by more than 20%. This study provides a theoretical basis for the research on wellbore cleaning tools.

Lab Model for a Low Power Wind Turbine System

Paper presents a lab low power wind turbine of 2.5 kW. The driving propeller is modeled with an assembly of variable frequency converter, three-phase induction motor and speed reducer. Thus the motor's speed can be easily driven in the range of (300 – 1500) rpm and its size is little. The speed reducer lowers the speed 5 times so that the generator will spin in the range (60 – 300) rpm. This range is usual for the propellers of wind turbines. In the end the trials of the system are presented using a specific data acquisition system.

Numerical Investigation of the Influence of Cavitation on the Runner Speed at Speed-No-Load and Runaway for a Francis Turbine of Low Specific Speed

Abstract Studies have shown that the runner speed of hydraulic turbines at no-load conditions is affected by cavitation. However, those studies did not provide explanations relating the variation of the no-load runner speed to cavitation. Understanding why cavitation affects the runner speed is crucial because the maximum runner speed is reached in no-load condition, and this speed must remain below a limit to ensure the generator's safety. This paper uses numerical simulations to investigate the effect of cavitation on two no-load conditions, the runaway and the speed-no-load, for a low specific speed Francis turbine at model scale. The study is based on unsteady Reynolds-averaged Navier–Stokes simulations with and without cavitation and focuses on averaged quantities. At no-load, the regions over the blades producing a motor torque, i.e., oriented with the turbine rotating direction, must be balanced by regions producing a braking torque, opposed to the turbine rotation, to achieve a zero-torque condition. At runaway, cavitation mainly affects regions where a motor torque is produced. However, the zones affected by cavitation have a small contribution to the total motor torque. Therefore, for the runaway condition studied, the torque balance over the blade is hardly affected by cavitation, and the impact of cavitation on the runaway speed is negligible. At speed-no-load, comparisons between cavitating and noncavitating simulations indicated that cavitation affects mainly the braking torque regions. Those regions result from an interaction between the runner blades and a backflow extending from the draft tube cone to the runner outlet. In that case, cavitation strongly affects the torque balance over the blades, and consequently, the runner speed will adapt to find another zero torque condition.

CFD and Taguchi based optimization of air driven single stage partial admission axial turbine blade profiles

Single-stage axial flow turbines are typically used in underground mining machines and underwater vehicles due to their safety and small size. However, the high-pressure ratio and small mass flow rates force the flow inside the turbine to be supersonic. The blade design of such turbines with high-flow velocity leads to high losses and low turbine efficiencies at conventional design values. In this paper, the 1D design of the turbine is carried out using the meanline design method. The results of the design algorithm are compared with both experimental, CFD (Computational Fluid Dynamics), and a well-known commercial software AxSTREAM. After validating the design, Taguchi method is used to analyze 6 different parameters (Blade Shape, Nozzle Shape, Cord Length, Solidity Ratio, Nozzle Angle and Blade Thickness) affecting the turbine performance and the optimum blade profile is compared with the conventional blade design. The optimum design isentropic efficiency (68.267%) outperformed the conventional design turbine isentropic efficiency (61.759%) by about 11%. This paper provides a different insight into the conventional turbine design method.

Characterization of a low power wind turbine prototype for interconnection to the grid

Characterization of a low power wind turbine prototype for interconnection to the grid

Supervised learning-based multi-site lean blowout prediction for dry low emission gas turbine

Current dry low emission (DLE) gas turbines have extremely low nitrogen oxides (NOx) emissions, allowing them to comply with stringent environmental regulations. The ultra-low temperatures required to achieve such low emissions also increase the risk of a lean blowout (LBO). DLE gas turbines are particularly vulnerable to LBO, which can lead to system instability, higher carbon oxides (CO) emissions, damaged components, substantial financial losses and environmental damages. In this regard, this current study proposes a novel supervised learning-based prediction technique with efficient performance on out-of-distribution data from multiple DLE gas turbine plants (multi-site). The proposed prediction approach exploits the competitive advantages of both adaptive boosting (AdaBoost) and Linear support vector machine (LSVM) to improve the generalization capability as well as prediction accuracy. The proposed algorithm was trained and tested using a real-world DLE gas turbine dataset from six different sites. The result indicates that the proposed model consistently achieving LBO prediction accuracy rates above 99.9% and Mathew’s correlation coefficient (MCC) score above 0.9 across all datasets. All lean-premixed gas turbines could benefit from the developed Ada-LSVM, as it is an accurate model with a high generalization performance that can be used across multiple sites.

INVERTED BRAYTON CYCLE ENGINE OPTIMIZATION FOR HYPERSONIC FLIGHT

Optimization of inverted Brayton cycle engine is made by particle swarm optimization method in this study. The optimum specific thrust value is reached by staying within the optimization constraints. When the total temperature of the cooling section is examined, it is seen that a temperature above the freezing temperature of the air is obtained. A very high specific thrust value, 451 N.s/kg is obtained at the hypersonic flight Mach Number (5 Mach) as a result of optimization. Temperature decrease with increasing altitude effect performance dramatically as positive. Low preburner exit total temperature and turbine total pressure ratio values and high afterburner exit total temperature values are desirable in terms of performance but values of total temperature at cooling section effect performance conversely in terms of specific thrust and specific fuel consumption

Clocking effects on aerodynamics of a gas turbine low pressure axial turbine, part 2: Unsteady simulation

Unsteady, viscous compressible flow is numerically simulated within first two stages of a low pressure turbine of a gas turbine engine under different clocking of its stator blades rows. Zonal DES turbulence modeling has been used for flow simulations. Time-dependent wake flow trajectory is modeled and visualized within the blades passages. All characteristics of the passage wake flow, including its V-shape motion, re-orientation, elongation, expansion, and stretching, are properly simulated. Unsteady flow field results together with those of general aerodynamic performance of the optimum and worst clocking cases are presented and compared with each other. Analyses of the flow simulation results showed that the optimum clocking of the blades rows occurs while the upstream wake flow impinges on the downstream stator blade leading edge region. Final results demonstrated that under the optimum clocking of the second stator, the inlet total pressure of the second rotor blades row and its output power increase by 0.1% and 0.336%, respectively. Consequently, efficiency of the second stage increases by 0.35%. In addition, total output power of the whole two stages increases by 0.237%.

Preliminary theoretical design of crossflow water turbine for rainwater rooftop harvesting system

Harvesting energy is essential especially now that the demand of energy is high but the fuel supply is limited. This study theoretically designs the 5 m low head crossflow turbine in rainwater harvesting system. The characteristics of the site condition, the runner geometry, the blade geometry, and the turbine specification had been identified and the geometrical model of the design is shown. This paper reported the collection of theoretical formula for the design of low head crossflow turbine that can be used for rainwater harvesting system. The dimensional form of equations, as presented in Section 2, resulted to the two, four, and two parameters that represent the dimensions of the turbine, runner and the blade, respectively. As a conclusion, the designed turbine can be used for rainwater harvesting system with an efficiency that was calculated to be 88% with 22 kW expected power generated for 5 m head.

Design of a low velocity wind turbine blades for power generation: part I‐aerodynamic performance

Design of a low velocity wind turbine blades for power generation: part I‐aerodynamic performance

Energy, exergy and economic (3E) analysis and multi-objective optimization of a combined cycle power system integrating compressed air energy storage and high-temperature thermal energy storage

Traditional adiabatic compressed air energy storage system has a low turbine efficiency and a low power output due to the low turbine inlet temperature and high turbine outlet temperature without heat recovery. To address these issues, a combined cycle power system integrating compressed air energy storage and high-temperature thermal energy storage is proposed in this paper. The thermodynamic and economic models of the proposed system are developed considering the thermodynamic laws and life cycle assessment, respectively. The energy, exergy, economic (3E) analysis of the system are performed based on the models. The results show that under the design condition, the round-trip efficiency, exergy efficiency, energy storage density, levelized cost of energy and dynamic payback period of the system can reach 59.22 %, 62.12 %, 5.77 kWh/m3, 0.1186 $/kWh and 6.51 years, respectively. The sensitivity analysis shows that the maximum air storage pressure, minimum air storage pressure and outlet temperature of high temperature thermal energy storage system are the critical parameters impacting the system performance. Finally, the multi-objective optimization of the proposed system is carried out. The aforementioned three parameters are selected as the decision variables and the round-trip efficiency and levelized cost of energy are chosen as the objective functions. Compared with the pre-optimization system, the round-trip efficiency, exergy efficiency, and energy storage density of the system increase by 0.47 %, 0.43 %, and 1.33 kWh/m3, respectively, while the levelized cost of energy and dynamic payback period decrease by 0.0051 $/kWh and 1.55 years, respectively.

Aerodynamic Study of Chord Length Effect in Low Speed Wind Turbine Using 6 DoF CFD Method

The dependencies on fossil energy as a basic energy source has many negative impacts, therefore alternative energy is needed to overcome the problem, one of which is the alternative green energy wind turbines. However, wind turbines in Indonesia are difficult to implement because the wind speed in Indonesia is low, which is around 4-8 m/s, therefore it is necessary to do research to improve the ability of wind turbines applied in Indonesia. The analysis method using the 6 DoF CFD method and the experimental carried out using the wind tunnel. The blade used in this study is a custom combination airfoil with the chord lengths of 0.1 m, 0.15 m and 0.2 m. The results shows that, at wind speed of 8 m/s the blade with a chord length of 0.2 m has the greatest pressure of 47 Pa and rotational speed per minute of 76.1 rpm, this variation can be applied to low rpm generators. Whereas blades with a chord length of 0.1 m and a twist angle of 15o have a pressure of 47 Pa, and rotational speed of 97.24 rpm per minute, this variation can be applied to high rpm generators.

Innovative Air Bypass System for Low-Emission Multi-Can Combustors

Abstract Gas turbines that are used as compressor drives are often operated in the part load regime because compressor stations are usually designed for operation with full power at extreme weather conditions. Consequently, these gas turbines must comply with strict emission regulations at unfavorably low turbine inlet temperatures. To extend the low-emission operation range of the premixed combustion systems, many gas turbines bypass a part of the compressed air upstream of the combustor and either blow it off into the exhaust stack or reinject it into the secondary combustion zone. This study presents a new approach that overcomes shortcomings by injecting the compressed air in the burner head in the vicinity of the primary combustion zone. This is particularly attractive for multi-can combustors. Atmospheric combustion tests are conducted for two different air injection designs. The first design features lower air injection velocity and the second features higher injection velocities. Both injection strategies are tested with the industrial MGT gas turbine can combustor. The full size burner is tested at atmospheric conditions in a burner test rig with a quartz flame tube and natural gas as fuel. The performance of the air bypass system is assessed by means of CO and NOx emission measurements for different air bypass ratios. Additionally, OH* chemiluminescence camera pictures are presented and compared to numerical calculations. It is found that the air injection in the annular vicinity of the swirl flame does not cause increased CO emissions by quenching or other effects.

Frequency control using electric vehicles with adaptive latency compensation and variable speed wind turbines using modified virtual inertia controller

In this paper, to reduce the effect of low inertia consequences, electric vehicle (EV) and variable speed wind turbine (VSWT) are adopted to collaborate in the power system frequency regulation. A virtual inertia controller based on the IEC 61851 standard is proposed to benefit from EV contribution in frequency regulation. In this controller, the rate-of-change-of-frequency (ROCOF) is measured and an appropriate EV current set point is obtained. Furthermore, to decrease the effect of frequency regulation on EVs owners, a stochastic allocation method of the regulation sequence among EVs parking lots is presented. One of the barriers of employing EV in the frequency regulation is the communication latency. To overcome this issue, according to the measured latency, a weighted combination of several compensators which is called adaptive latency compensator (ALC) is utilized. After compensating the delay, the output power of the EVs is calculated and collaborated in frequency regulation. In addition, an algorithm is proposed for collaborating VSWT in frequency control. In the proposed algorithm, according to the wind velocity, the output power of the VSWT increases to the maximum acceptable value and will be fixed. A method is developed to find the maximum acceptable increment power considering VSWT constraints. After a supportive part, a recovery part is started to return VSWT hub speed to a desired value. Two PID controllers are designed in this algorithm for support and recovery parts. During the recovery part, a second frequency dip emerges and a method is introduced which at first identifies the second frequency dip moment and EVs collaboration is applied to alleviate this unfavorable outcome. To evaluate the performance of the proposed algorithms and controllers, different simulation studies are conducted using the modified IEEE 39-bus test power system. Results confirm the effectiveness of the proposed methods in system frequency support.

Design and analysis of an axial turbine for high-temperature organic Rankine cycle

The organic Rankine cycle (ORC) system is of great importance to achieving the effective exploitation of waste energy. As the essential component of the ORC system, the expander is directly related to the performance and structure size of the ORC system, which deserves to be studied in detail. A single-stage axial turbine with a U-shaped volute is presented for the high-temperature ORC system in this paper. Based on preliminary design and modeling, the turbine aerodynamic performance under design and off-design conditions is investigated in numerical simulation. Results show that the turbine efficiency is 77% with a pressure ratio of 4.78 at the design point and the turbine efficiency can still be maintained above 70% as the pressure ratio reaches 6. It can be concluded that low Reynolds number flow and negative incidence angle are the main reasons for low turbine efficiency under the low pressure ratio, while the shock wave becomes the key factor influencing turbine efficiency under the high pressure ratio. In addition, blade profile optimization and shock wave management is the primary way to maintain high turbine efficiency under a high pressure ratio. Results indicate that the turbine proposed in this paper is proven suitable for high-temperature ORC systems and the relevant research has a certain guiding value for the efficient and compact single-stage axial turbine design.

Research and Justification of the Parameters of the Wind Wheel of a Low-power Wind Power Plant for Various Purposes

The implementation of small wind turbine projects will increase the volume of commissioning of RES electrical capacities, an indicator of the National project «Sustainable economic growth aimed at improving the welfare of Kazakhstanis». In this paper, the efficiency of a low-power wind power plant is investigated. The aim of the work is to study the parameters of the wind wheel of a low power wind turbine with the smallest hub diameter. The main tasks set in this study are: conducting a study of the dependence of the torque of rotational speed and power developed by the wind wheel on its design parameters. A comparative analysis of the efficiency of wind turbines for generating electrical energy and lifting water has been carried out. The study was carried out on a laboratory model of a wind turbine. This article draws a number of conclusions on the use of the design parameters of the wind wheel, depending on the purpose of the wind turbine

A NEW SEAWATER LOW-HEAD TURBINE FOR THE OBREC

The OBREC (Overtopping Breakwater for wave Energy Conversion) is based on the overtopping phenomenon [1] where incoming waves run over an overtopping ramp and fall into a reservoir located above the sea level inside a conventional rubble mound breakwater, or into a vertical caisson breakwater. The wave energy is transformed into potential energy, with some contribution of kinetic energy. Then, the flow is driven through a turbine addressing the final transformation into electrical energy. The OBREC prototype is located in the middle of the San Vincenzo breakwater, in Naples harbour (Italy). The key target of the whole pilot project was to demonstrate the high capacity factor of the system (expressed as the ratio of the electrical energy produced to the electrical energy that could have been produced at continuous full power operation), even in a low-energy wave climate. At the study site, in fact, the yearly average wave power was found to be 1.8 kW/m over the last 42 years [2]. However, during last 5 years, a maximum wave height of over 5 m has been registered, confirming the high reliability under severe wave conditions.
 Due to the short monitoring period and to the undersize of the previous power take-off (PTO) systems, no definitive power matrix is available for OBREC [3]. The energy conversion efficiency of OBREC has been deeply investigated over the last years through both physical and numerical model tests. Within the ongoing full-scale monitoring activities in real environments, a new set of power take-off was installed. A propeller-type pico-turbine equipment was in 2021, and its final setting was completed in 2022. Performance and reliability of the entire structure were closely monitored under different “stress tests”, i.e. start & stop cycle in marine environment with a high variable combination of flow rate/hydraulic head.
 This paper presents the design stage for the new equipment and preliminary results from these tests numerical and field tests.
 
 
 Contestabile, P., Crispino, G., Di Lauro, E., Ferrante, V., Gisonni, C., & Vicinanza, D. (2020). Overtopping breakwater for wave Energy Conversion: Review of state of art, recent advancements and what lies ahead. Renewable Energy, 147, 705-718.
 Contestabile, P., Russo, S., Azzellino, A., Cascetta, F., Vicinanza, D. (2022). "Combination of local sea winds/land breezes and nearshore wave energy resource: Case study at MaRELab (Naples, Italy)", Energy Conversion and Management, ISSN 0196-8904, 257, 115356, https://doi.org/10.1016/j.enconman.2022.115356 
 Mariani, A., Crispino, G., Contestabile, P., Cascetta, F., Gisonni, C., Vicinanza, D., & Unich, A. (2021). Optimization of Low Head Axial-Flow Turbines for an Overtopping BReakwater for Energy Conversion: A Case Study. Energies, 14(15), 4618.

Reheat effect on the improvement in efficiency of the turbine driven by pulse detonation

Due to the strong unsteadiness of pulse detonation, large flow losses are generated when the detonation wave interacts with the turbine blades, resulting in low turbine efficiency. Considering that the flow losses are dissipated into the gas as heat energy, some of them can be recycled during the expansion process in subsequent stages by the reheat effect, which should be helpful to improve the detonation-driven turbine efficiency. Taking this into account, this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine, and a stoichiometric hydrogen-air mixture was used. The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine. The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation, which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled, so that the efficiency of the two-stage turbine was improved. At a 95% confidence level, the efficiency improvement was stable at 4.5%–5.3%, demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.

Assessment of erosion wear in low specific speed Francis turbine due to particulate flow

The erosion wear of turbine components reduces the turbine life and consequently decreases the efficiency or power generation. In the present work, the effect and cause of erosion wear in a high head Francis turbine are investigated through the measurements and numerical simulations on a prototype turbine. Localised erosion patterns are observed over the surface of the guide vane, runner, faceplate, and labyrinth seal due to existing particulate flows. Further, the physical interpretation of erosion wear mechanisms is studied through numerical simulations, and the eroded zones of different components are qualitatively validated with the actual site in-situ measurements. The erosion rate prediction of the turbine components is performed by employing a recently developed erosion model for CA6NM turbine material. The results show that the continuous interblade vortex with significant velocity and crossflow between the blade passages is found accountable for the severe erosion of the runner shroud. The dominating effect of flow instability at the off-design operation depicts higher erosion of turbine components. Moreover, the exponent value for the particle size is found to vary in the range of 1.16–1.30 for the material removal rate of turbine components.

Axial water jet injection in a low head Francis turbine at part load

The part load operation of a Francis turbine generally develops a rotating vortex rope (RVR) in the draft tube, generating flow instabilities and pressure pulsations. The present work reports the axial water injection method to mitigate the RVR and its associated pulsations in the draft tube. The runner cone is modified to install a nozzle of three different designs for water jet injection. Water is injected axially at the rate of 0.5% to 2% of the main flow. Spectral analysis is performed to assess the pressure amplitude and dominating frequency affected by the water injection. Spectrogram and spatial harmonic decomposition show a reduction in synchronous and asynchronous pulsation amplitudes. The pressure recovery in the draft tube cone is also improved. The spectral analysis shows that the water injection at 1% and 1.25% is the most effective. The water injection above 1.25% to 2% causes pulsations near the draft tube bend as the water jet bounces back after striking the elbow. A sharp decrease in the Strouhal frequency is observed above 0.5% jet injection. The efficiency of the turbine is also improved by water jet injection.