Turbine Loss Research Articles

Demonstration of a fault impact reduction control module for wind turbines

Abstract. Traditionally, wind turbines in distributed applications make control decisions as isolated systems. They generally provide maximum power output during operation and manage internal faults with little consideration of the rest of the power system. Although fault detection and tolerance schemes are widely researched and implemented, controls to ameliorate such faults are uncommon in research and industry. The rapid shutdown of a wind turbine in a large transmission-connected wind plant will have a minimal impact on a large power system, but in a microgrid or isolated grid context the abrupt loss of a single wind turbine may cause grid instability and high stress on the system. This paper demonstrates a fault impact reduction control (FIRC) module for a wind turbine, which implements wider warning thresholds around fault thresholds. When the turbine crosses a warning threshold, the controller sends its predicted action to the grid controller, which facilitates the grid operator’s response to a potential wind turbine fault and then takes appropriate action to ameliorate the fault. Various test cases demonstrate the controller action under a variety of faults, and various scenarios demonstrate the grid benefit of an FIRC in both microgrid- and grid-connected contexts. The FIRC maximizes wind turbine generation and eases generation transition under a variety of fault scenarios. The FIRC module is easy to integrate with most existing controllers, just requiring derate capability, and can be easily modified to include the various warnings and thresholds that the user desires. This analysis is mainly performed in a MATLAB-Simulink-based research wind turbine model and is also implemented in the existing LabVIEW-based controller of the same research turbine at NREL.

Performance and flow characteristics of the liquid turbine for supercritical compressed air energy storage system

• Geometrical models of liquid turbines affect the accuracy of predicted efficiency. • The model with a nozzle and a rotor predictes the efficiency with 15.8% error. • The total pressure loss of the rotor accounts for the largest portion among all parts. • The nonuniform flow in the nozzle and the rotor is significant at low flow rates. The liquid turbine can replace throttling valves during the depressurization process of high-pressure liquid or supercritical fluid and improve the system efficiency of many industrial systems. However, there is no research about studying the internal flow and total pressure loss of liquid turbines, which can affect the turbine performance significantly. In this paper, performance and flow characteristics in a liquid turbine were analyzed for supercritical compressed air energy storage (SC-CAES) systems in the first time. Three typical topology models (C1, C2 and C3) of the tested liquid turbine were simulated and their performances were compared with experimental results. The deviation of the turbine efficiency between C3 and the experiment was less than 2%, while C1 had a constant increment of the turbine efficiency about 15.8% with the experiment. The total pressure loss in each part was evaluated and the flow characteristics in the nozzle and the rotor were analyzed. Nonuniform flow affected the nozzle’s total pressure loss significantly, while the rotor’s total pressure loss was related to the development of low energy regions. The results obtained in this paper provides guidance for optimizing liquid turbines and improving the turbine performance for various industrial systems with throttling valves installed.

Experimental and numerical approach for characterization and performance evaluation of cryogenic turboexpander under rotating condition

A small-scale radial expansion turbine is distinguished by its ease of production, higher efficiency, and reliability. Such turbines have been successfully used in cryogenic turboexpander systems for refrigeration and liquefaction of the process gas. This paper presents a methodology for design optimization, numerical, and experimental investigation of a radial turbine and nozzle (turboexpander), the most necessary and extortionate component of a nitrogen liquefaction system based on Claude cycle. The initial investigation starts with the preliminary design of a turboexpander using an in-house developed Matlab® code. Then, a Sobol method-based optimization approach has been proposed to determine the normalized sensitivity index and optimal range of major non-dimensional and geometrical variables for the better off-design performance of the turboexpander. After that, different losses of the turbine have been determined using an optimum set of loss correlations which is incorporated into the preliminary design process. This approach can overcome the optimization issues caused by the high sensitive design parameters, which may not be addressed through conventional methods, and ameliorates the off-design performance of the turboexpander (improves power output, total-to-static efficiency, and diminishing the turbine losses by 14.28%, 3.89%, and 9.61% respectively) as compared to the initial design. Based on this, three turboexpander systems are designed and a comparative numerical study has been conducted to study the flow field phenomenon and their thermodynamic performance at three operating pressure and cryogenic temperature (16 bar & 150 K, 8 bar & 120 K, and 4.5 bar & 95 K) using ANSYS CFX®. Finally, the Claude cycle-based experimental facility has been established to determine the thermal performance of the turboexpander at various operating pressure (16 and 8 bar), rotational speeds (120,612, 102,419, and 80,914 rpm), inlet temperatures (150 and 120 K), and mass flow rates (0.01–0.10 kg/s). The results illustrate that the predicted performance from the numerical simulation shows good agreement with the experimental results. Additionally, error analysis of experimental parameters has also been discussed.

The Effect of Inlet Conditions on Turbine Endwall Loss

Abstract There can be significant variation and uncertainty in the flow conditions entering a blade row. This article explores how this variability can affect endwall loss in axial turbines. A computational study of three cascades with collinear inlet boundary layers is conducted. Endwall loss varies by more than a factor of 3 depending on the inlet conditions. This variation is caused by dissipation of secondary kinetic energy (SKE). The results can be understood by observing that the inlet conditions predominantly control how secondary vorticity is distributed within the blade passage. Modestly thick inlet boundary layers with high shape factor tend to displace vorticity toward the center of the passage. This displacement reduces vorticity cancellation, increasing secondary velocities, and SKE. A general method is formulated to estimate SKE in preliminary design. Optimum aspect ratio is shown to depend on the inlet boundary condition. Strategies to reduce endwall loss and minimize sensitivity to inlet conditions are then highlighted.

A comparison of axial turbine loss models for air, sCO[formula omitted] and ORC turbines across a range of scales

Loss models are used to evaluate the aerodynamic performance of axial turbines at the preliminary design stage. The commonly used loss models were derived for air and steam turbines and have not been sufficiently investigated for turbines working with non-conventional working fluids, relevant to new power systems, such as organic fluids and supercritical CO2 (sCO2). Thus, the aim of this study is to explore the deviation between the performance predictions of different loss models, namely Dunham and Came, Kacker and Okapuu, Craig and Cox and Aungier, for non-conventional working fluids where turbines may differ in design and operation than conventional air or steam turbines. Additionally, this paper aims to investigate the effect of the turbine scale on the trends in the performance predictions of these models. Three different case-studies are defined for air, organic Rankine cycle (ORC) and sCO2 turbines and each one is evaluated at two different scales. It is found that the selected loss models resulted in varying loss predictions; particularly for predicting the losses due to the clearance gap for all small scale designs. Furthermore, large variations were found in predicting the effect of the flow regime on the turbine performance for all models.

On wind turbine's loss of synchronisation during severe faults

AbstractGrid codes mandate that wind turbines (WTs) remain connected even during severe faults. This requirement can lead to WTs' loss of synchronisation (LoS) with the AC grid under severe symmetrical faults. In this paper, the LoS is illustrated by the power balance principle. Then, a solution with improved performance for avoiding LoS during severe faults is proposed, implemented and verified by simulations. The results show that the solution eliminates the steady‐state frequency deviation during faults, resulting in a smoother WT transient during and post‐fault.

Turbine power loss during yaw-misaligned free field tests at different atmospheric conditions

This paper presents an analysis of the power loss of the upstream turbine for yaw misalignment depending on the inflow condition. High-quality experimental field data, obtained from a lidar wind profiler, met mast, GPS based yaw sensor, turbine data, and load data is used. To reduce the spreading of the power loss during yaw misalignment, the rotor effective wind speed is estimated using load data. Furthermore, the so-called power loss coefficient currently used in most engineering models, for yaw misalignment, is assessed at various inflow conditions. As main finding, the power loss coefficient increases for stronger vertical wind shear. In addition, there is an asymmetry with respect to the direction of the yaw misalignment that is enhanced by the wind shear exponent and the wind veer. Neglecting these two effects could result in in-conservative wake-steering decisions at stable stratification

Factors influencing wind turbine avoidance behaviour of a migrating soaring bird

Wind energy production has expanded as an alternative to carbon emitting fossil fuels, but is causing impacts on wildlife that need to be addressed. Soaring birds show concerning rates of collision with turbine rotor blades and losses of critical habitat. However, how these birds interact with wind turbines is poorly understood. We analyzed high-frequency GPS tracking data of 126 black kites (Milvus migrans) moving near wind turbines to identify behavioural mechanisms of turbine avoidance and their interaction with environmental variables. Birds flying within 1000 m from turbines and below the height of rotor blades were less likely to be oriented towards turbines than expected by chance, this pattern being more striking at distances less than 750 m. Within the range of 750 m, birds showed stronger avoidance when pushed by the wind in the direction of the turbines. Birds flying above the turbines did not change flight directions with turbine proximity. Sex and age of birds, uplift conditions and turbine height, showed no effect on flight directions although these factors have been pointed as important drivers of turbine collision by soaring birds. Our findings suggest that migrating black kites recognize the presence of wind turbines and behave in a way to avoid then. This may explain why this species presents lower collision rates with wind turbines than other soaring birds. Future studies should clarify if turbine avoidance behaviour is common to other soaring birds, particularly those that are facing high fatality rates due to collision.

Design and optimization of supersonic turbines for detonation combustors

Detonation-based engines offer a potential surge in efficiency for compact thermal power systems. However, these cycles require ad-hoc components adapted to the high outlet velocity from the detonation combustors. This paper presents the design methodology of turbine stages suitable for supersonic inlet conditions and provides a detailed analysis of optimized turbine geometries. A reduced-order solver examines the supersonic blade rows’ functional design space, quantifies the turbine’s non-isentropic performance, and budgets the turbine loss for different optimized leading-edge designs and chord to pitch ratios. The shock-wave interactions were identified as the predominant contributor to turbine losses, and optimal pitch-chord ratios were determined for various inlet Mach numbers. Finally, with this tool, the specific-power output for a wide range of design configurations was computed; and the metal angle that ensures flow starting and maximizes power extraction was calculated. The detailed numerical study describes the flow interactions in a supersonic turbine and offers new correlations to guide the design of future supersonic turbines.

Distribution Characteristics of High Wetness Loss Area in the Last Two Stages of Steam Turbine under Varying Conditions

Wetness loss of a steam turbine seriously affects the security of the unit when operating in deep peak regulation. To obtain the distribution characteristics of the high wetness loss area under different working conditions, especially low-load conditions, the last two stages of the low-pressure cylinder (LPC) of a 600 MW steam turbine were simulated using the non-equilibrium condensation model proposed in this study. The nucleation rate distribution, supercooling degree, and steam velocity droplet were analyzed. Consequently, the diameter distribution of coarse water droplets under 100%, 50%, 40%, 30%, and 20% THA conditions and the distribution of the thermodynamic loss and water droplet resistance loss were obtained. Thermodynamic loss mainly occurred at the front end of second-stage stator blades and trailing end of the last-stage stator blades. The water droplet resistance loss mainly occurred at 40% of the blade height and at the tip of the last-stage stator blades. Moreover, with a reduction in the unit load, the thermodynamic loss continued to decrease, but the water droplet resistance loss continued to increase.

Insight into the effects of leading edge delamination on the aerodynamic performance of an airfoil and wind turbine

Severe erosion or delamination at the leading edge of blades has an adverse influence on the power loss of wind turbines. Obtaining relevant quantitative data and its mechanisms would help in the efficient management and maintenance of these turbines. In the present work, detailed analysis on the effects of various levels of leading edge delamination on the aerodynamics and flow characteristics of an S809 airfoil and, in turn, on the performance of the NREL phase VI rotor is conducted. The results indicated that an elongated leading edge separation bubble and two enclosed vortex systems appeared in the delaminated region of the airfoil when the delamination levels aggravate to a certain degree, while the trailing edge separation vortex can be observed for all delaminated airfoils. The aerodynamic performance of the wind turbine decreases with increasing delamination depth and increases with growing delamination depth. The most influential delamination length is 1%c, and the maximum power loss is 23.09% for the blade with the severe delamination case. A small area of deep leading edge delamination or defects may cause great power loss, which should not be ignored in practice engineering.

A Review on the Estimation of Power Loss Due to Icing in Wind Turbines

The objective of this article is to review the methodologies used in the last 15 years to estimate the power loss in wind turbines due to their exposure to adverse meteorological conditions. Among the methods, the use of computational fluid dynamics (CFD) for the three-dimensional numerical simulation of wind turbines is highlighted, as well as the use of two-dimensional CFD simulation in conjunction with the blade element momentum theory (BEM). In addition, a brief review of other methodologies such as image analysis, deep learning, and forecasting models is also presented. This review constitutes a baseline for new investigations of the icing effects on wind turbines’ power outputs. Furthermore, it contributes to a continuous improvement in power-loss prediction and the better response of icing protection systems.

Energy loss of radial inflow turbine for organic Rankine cycle using mixture based on entropy production method

The radial inflow turbine is the core component of the organic Rankine cycle(ORC) system. Based on the internal flow field of the turbine analyzed by computational fluid dynamics (CFD), the energy dissipation of a radial inflow turbine with variable guide vane is determined by the entropy production analysis method. In the presented work, the mixture of R245fa/R134a is selected as the working fluid, and the effects of tip clearance and mixing ratio on the flow loss characteristics are investigated. The results show that the high entropy production region in the stator is caused by leakage vortex and shock phenomenon, while the passage vortex and leakage vortex are the reasons for the high loss area in the rotor. The total volume entropy production of rotor is mainly composed of the passage zone, which is significantly higher than that of the stator. As the tip clearance increases from 3% to 10%, the total entropy production of stator and rotor increases by 54.5 and 161.7% respectively, and the output power and isentropic efficiency of the turbine decrease by 14.7% and 14.6% respectively. With the increase of R245fa mass fraction, the total volume entropy production of the stator and rotor decreases linearly. Compared with R134a, the turbine isentropic efficiency of R245fa increases by 3.1%.

Evaluation of novel integrated combined cycle based on gas turbine-SOFC-geothermal-steam and organic Rankine cycles for gas turbo compressor station

Heat loss of gas turbines (GTs) in gas stations on the one hand and increasing power consumption, on the other hand, makes attractive heat recovery and the use of power generation cycles in these stations. In this paper, an integrated combined cycle including GTs, solid oxide fuel cell (SOFC), steam and organic Rankine cycles (SORCs) have been proposed for compressor stations to produce extra power. The power generated by GTs is used to move the natural gas compressors. Hot gases from GTs and fuel cell (FC) provide the required thermal power of SORCs. Also, the part of thermal load in the organic Rankine cycle (ORC) is supported by geothermal energy. Energy, Exergy, Exergoeconomic, Emergoeconomic, , and Emergoenvironmental (6E) analyses along with advanced exergy, exergoeconomic, and exergoenvironmental evaluations provides a broad and comprehensive view to investigate the proposed cycle. Sensitivity analysis was performed to evaluate the roles of decision variables on the system effectiveness from different aspects. For ORC, five organic fluids were compared from the 6E analyses. The results show that the power production and thermal efficiency increase by about 21 MW (53.76%) and 13.07% compared with the base plant (a significant amount), respectively. The system's total cost and environmental impacts rates will be 2437.28 $/h and 1476.18 Pts/h, respectively. Levelized cost of electricity (LCOE) calculated 41.1 $/MWh that in the field of power systems is suitable. R11 was found as the best-recommended organic fluid. Rec2, SOFC, LPECO, and Rec1 are the highest capacity for improvement in terms of advanced analysis.

Optimization of a Francis Turbine Runner by Means of Inverse Design and CFD Calculation

A Francis turbine runner was optimized by a combination of means of the 3D Inverse Design Method and Computational Fluid Dynamics (CFD). An experiment of the directly optimized conventional turbine confirms the validation of CFD calculation. A new meridional shape was designed by Design of Experiments with CFD and the database of meridional shape factors. Angular momentum at the runner inlet was corrected to cover the effects of the boundary layer from runner upstream domains such as stay vanes and guide vanes. Using the meridional shape and the corrected angular momentum and considering the secondary flow mechanism, blade loading distribution and stacking condition were optimized. It led to the decrease of secondary flow energy near the runner inlet and of the runner loss. The full-domain CFD calculation confirms that the total loss of the new turbine at the design point is 4[%] lower than that of the conventional one. This result shows the 3D Inverse Design Method is practical to control the secondary flow in the Francis turbine runners and optimize the shape.

Comparative Study of Dynamic Stall between an Aircraft Airfoil and a Wind Turbine Airfoil in an Air–Particle Flow

Dynamic stall in clean air flow has been well studied, but its exploration in air–particle (air–raindrop or air–sand) flow is still lacking. The aerodynamic performance loss of aircraft (NACA0012) and wind turbine (S809) airfoils and their differences during the hysteresis loop at different pitching parameters are also poorly understood. As shown in this paper, the reduced frequency has little effect on the value of the maximum lift coefficient increment caused by particles, but a larger one can enhance the hysteresis effect and drag the angle of attack, at which the maximum increment is obtained, from the up stroke to the down stroke. The large lift coefficient increments of two airfoils and their difference also have a similar change trend with the reduced frequency. Compared to that of NACA0012 airfoil, the increments of S809 airfoil are obviously greater at three mean angles of attack, especially at 8°, which is the commonly used operating angle. In addition, the angle of attack, at which the maximum lift coefficient is obtained, can be significantly changed by particles in two regions: one is under the effect of deep stall, the other is under the effect of light stall at a low, reduced frequency.

Results from a wake-steering experiment at a commercial wind plant: investigating the wind speed dependence of wake-steering performance

Abstract. Wake steering is a wind farm control strategy in which upstream wind turbines are misaligned with the wind to redirect their wakes away from downstream turbines, thereby increasing the net wind plant power production and reducing fatigue loads generated by wake turbulence. In this paper, we present results from a wake-steering experiment at a commercial wind plant involving two wind turbines spaced 3.7 rotor diameters apart. During the 3-month experiment period, we estimate that wake steering reduced wake losses by 5.6 % for the wind direction sector investigated. After applying a long-term correction based on the site wind rose, the reduction in wake losses increases to 9.3 %. As a function of wind speed, we find large energy improvements near cut-in wind speed, where wake steering can prevent the downstream wind turbine from shutting down. Yet for wind speeds between 6–8 m/s, we observe little change in performance with wake steering. However, wake steering was found to improve energy production significantly for below-rated wind speeds from 8–12 m/s. By measuring the relationship between yaw misalignment and power production using a nacelle lidar, we attribute much of the improvement in wake-steering performance at higher wind speeds to a significant reduction in the power loss of the upstream turbine as wind speed increases. Additionally, we find higher wind direction variability at lower wind speeds, which contributes to poor performance in the 6–8 m/s wind speed bin because of slow yaw controller dynamics. Further, we compare the measured performance of wake steering to predictions using the FLORIS (FLOw Redirection and Induction in Steady State) wind farm control tool coupled with a wind direction variability model. Although the achieved yaw offsets at the upstream wind turbine fall short of the intended yaw offsets, we find that they are predicted well by the wind direction variability model. When incorporating the expected yaw offsets, estimates of the energy improvement from wake steering using FLORIS closely match the experimental results.

A methodology for loss and performance assessment of a variable geometry turbocharger turbine through a new meanline FORTRAN program

PurposeVariable geometry turbine (VGT), a key component of modern internal combustion engines (ICE) turbochargers, is increasingly used for better efficiency and reduced exhaust gas emissions. The aim of this study is the development of a new meanline FORTRAN code for accurate performance and loss assessment of VGTs under a wider operating range. This code is a useful alternative tool for engineers for fast design of VGT systems where higher efficiency and minimum loss are being required.Design/methodology/approachThe proposed meanline code was applied to a variable geometry mixed flow turbine at different nozzle vane angles and under a wide range of rotational speed and the expansion ratio. The numerical methodology was validated through a comparison of the predicted performance to test data. The maps of the mass flow rate as well as the efficiency of the VGT system are discussed for different nozzle vane angles under a wide range of rotational speed. Based on the developed model, a breakdown loss analysis was carried out showing a significant effect of the nozzle vane angle on the loss distribution.FindingsResults indicated that the nozzle angle of 70° has led to the maximum efficiency compared to the other investigated nozzle vane angles ranging from 30° up to 80°. The results showed that the passage loss was significantly reduced as the nozzle vane angle increases from 30° up to 70°.Originality/valueThis paper outlines a new meanline approach for variable geometry turbocharger turbines. The developed code presents the novelty of including the effect of the vane radii variation, due to the pivoting mechanism of the nozzle ring. The developed code can be generalized to either radial or mixed flow turbines with or without a VGT system.

Statistical and Computational Evaluation of Empirical Axial Turbine Correlations in Design of Centrifugal Turbines

AbstractCentrifugal turbines have recently regained interest of the engineering community as they could serve as cost-effective alternatives in diverse energy applications. In this device, the working fluid expands in a centrifugal flowpath and entails rotation of concentric rings of airfoil-shaped blades. Yet in their current design paradigm, their meanline performance estimation and optimization have dubiously exploited axial turbine empirical correlations. To the authors knowledge, there are no theoretical nor practical foundation that could justify such practice. Hence, this paper intends to deliver an answer on this matter with application of the biased Kacker and Okapuu (KO) and Aungier (Ag) correlations on 33 pairs of similar axial and centrifugal cascades. The uncovered content is twofold. First, the Ag loss demonstrates a probability of achieving an error within ±15% of 44% whereas that of KO is lessened to 38% in axial cascades. The Ag deviation attains 15% which is thrice that of the KO under same condition. In second, the insensitivity of the Ag profile and secondary losses under drastic change of flow condition in the centrifugal cascades is proven to be practically significant. While the Ag deviation is still able to reach an accuracy of 11%. The coupling effect of the terms intervening in the correlations reveal to be weak. Thereupon, the empirical axial turbine loss correlations are unreliable in performance estimation or optimization of centrifugal turbines.

Energy analysis and optimization of a small-scale axial flow turbine for Organic Rankine Cycle application

Increasing the cycle efficiency of Organic Rankine Cycles is an important R&D area. In this study, an effort has been made to optimize various parameters related to the axial flow turbine to maximize an ORC's efficiency. First, a numerical model for a small-scale single-stage axial flow turbine was developed and coupled with a 1D model of an existing ORC system. Then, a parametric study was undertaken for the system working under various turbine inlet conditions, such as turbine pressure ratios and working fluids. An optimization study was undertaken for the turbine flow profile using a low computational intensity Artificial Neural Network coupled with Genetic Algorithm optimization. Investigating the turbine losses revealed that the Mach Number is the most influential factor, which depends on the molar mass of the working fluid. Our study revealed that increasing the degree of superheat by up to 200% enhanced the turbine and overall cycle efficiency by 11% and 5%, respectively. Increasing the turbine total-to-static pressure ratio from 3 to 10 improved the turbine and cycle efficiency by up to 41% and 15%, respectively. Optimizing the turbine's flow profile enhanced the overall loss coefficient by 13.7%, the turbine's total-to-static efficiency by 5.2%, and the overall cycle efficiency from 8.78% to 9.02%.