Turbine Stage Research Articles

Investigation of burnout effect in turbine blade tip leakage at transonic conditions – a numerical study

Abstract In the aviation industry, turbine blade tip leakage significantly impacts the economy due to aerodynamic losses in the turbine. The tip leakage flow increases when the tip surface is exposed to high heat loads from the burnout effect, contributing to nearly 30% of the total loss in the turbine stage. This study numerically investigates two-dimensional flat tip and burnt-out tip models under different flow accelerations at transonic conditions. Variations in the discharge coefficient are examined for different pressure ratios across the tip gap. Flow and shockwave patterns for various blade tip geometries are obtained and analyzed. The burnt-out tip notably increases tip leakage, and a significant decrease in turbine efficiency is observed beyond a critical burnout limit. The quantified losses at different stages of blade tip burnout are used to predict the effective operational life of the blade. A correlation is developed to relate the non-dimensional tip-leakage flow parameters to the normalized blade-tip geometry.

Noise Source Identification for the Unsteady Low-Pressure Turbine Flow Fields

Abstract The article presents a data processing methodology to identify the noise sources in low-pressure turbine (LPT) stages and their relative importance. Scale adaptive simulation (SAS) has been carried out on a geometry reproducing the midspan blade section of an entire LPT stage. The proper orthogonal decomposition (POD) is applied to data matrices constructed with the velocity and the pressure fields in order to distinctly extract the coherent structures responsible for velocity fluctuations and pressure waves (i.e., POD modes from the corresponding kernel), their temporal evolution and energies. The cross-correlation matrices of the pressure modes and the velocity modes reveal the degree of coupling between pressure and velocity oscillations, thus highlighting the modes linked to the same flow phenomena. The results show that the periodic vortex shedding at the stator trailing edge emits strong pressure waves, and the upstream-propagating waves reflect against the adjacent stator suction surface. The POD modes related to the rotor–stator interaction show peak amplitudes at the blade passing frequency and its harmonics and their shapes mimic the potential interaction in the stator domain and the migration of viscous wakes in the rotor domain. The POD modes with lower energy content correspond to the stochastic turbulent structures originated from the turbulent boundary layers as well as those carried by the vane and blade wakes. The biggest noise sources of the current flow fields are identified to be the von Karman vortex street downstream the stator trailing edge and the rotor–stator interaction.

Shape Optimization of a Diffusive High-Pressure Turbine Vane Using Machine Learning Tools

Machine learning tools represent a key methodology for the shape optimization of complex geometries in the turbomachinery field. One of the current challenges is to redesign High-Pressure Turbine (HPT) stages to couple them with innovative combustion technologies. In fact, recent developments in the gas turbine field have led to the introduction of pioneering solutions such as Rotating Detonation Combustors (RDCs) aimed at improving the overall efficiency of the thermodynamic cycle at low overall pressure ratios. In this study, a HPT vane equipped with diffusive endwalls is optimized to allow for ingesting a high-subsonic flow (Ma=0.6) delivered by a RDC. The main purpose of this paper is to investigate the prediction ability of machine learning tools in case of multiple input parameters and different objective functions. Moreover, the model predictions are used to identify the optimal solutions in terms of vane efficiency and operating conditions. A new solution that combines optimal vane efficiency with target values for both the exit flow angle and the inlet Mach number is also presented. The impact of the newly designed geometrical features on the development of secondary flows is analyzed through numerical simulations. The optimized geometry achieved strong mitigation of the intensity of the secondary flows induced by the main flow separation from the diffusive endwalls. As a consequence, the overall vane aerodynamic efficiency increased with respect to the baseline design.

The effect of working fluid and compressibility on the optimal solidity of axial turbine cascades

The blade solidity, namely the blade chord-to-pitch ratio, largely affects the fluid-dynamic performance of turbomachinery and its cost. For turbo-machines operating with air or steam, the optimal value of the solidity which maximizes the efficiency is estimated with empirical correlations such as the ones proposed by <xref ref-type="bibr" rid="fn19">Zweifel (1945)</xref> and <xref ref-type="bibr" rid="fn17">Traupel (1966)</xref>. However, if the turbomachine operates with unconventional fluids, the accuracy of these correlations is questionable. Examples of such fluids are the organic compounds (e.g., hydrocarbons, siloxanes) used in organic Rankine cycle (ORC) power systems. This study concerns an investigation on how the working fluid, its thermodynamic state, and flow compressibility influence the optimum pitch-to-chord ratio of turbine stages. A first principle reduced-order model (ROM) for the computation of profile losses was developed for this purpose. The ROM results are compared with those obtained from numerical simulations of the flow over two axial turbine cascade geometries. The influence of both the working fluid, the flow compressibility, and the solidity value on both the boundary layer state at the blade trailing edge and the base pressure are evaluated. Models to compute mixing and passage losses in the compressible regime as a function of the axial solidity are proposed and discussed. Results show that the value of the optimal solidity of turbine cascades significantly increases with the flow compressibility, and mildly increases if the fluid is in the dense vapor state. Moreover, the optimal solidity value is strongly affected by the mixing process occurring downstream of the blade trailing edge. Therefore, currently available models for its estimation, which are solely based on the minimization of the profile losses, are inaccurate.

Non-equilibrium condensation flow characteristics of wet steam considering condensation shock effect in the steam turbine

A non-equilibrium condensation flow occurs in steam turbines, accompanied by condensation shock. At present, there are limited studies on the influence of condensation shock on the flow and condensation characteristics of wet steam, and the unsteady influence of condensation shock on the flow field of wet steam always have been ignored. In this paper, the unsteady flow characteristics of condensation were presented by considering the condensation shock effect. First, the condensation flow models and corresponding source terms were programmed and loaded with UDS (user-defined scalar) and UDF (user-defined function), respectively, and the governing equations were discretized using a high-resolution calculation method. The calculated results agreed well with the reported experimental results. Based on the models, the non-equilibrium condensation flow characteristics with inlet and outlet pressures in Laval nozzle considering the condensation shock effect were analyzed. Finally, during the unsteady phase change process, the effects of back pressure and saturation of the inlet on the liquid phase parameters were examined considering the condensation shock effect in the Dykas cascade. The results show that a decrease in the back pressure and an increase in the inlet pressure improve the condensation shock intensity in Laval nozzle. With the increase of condensation shock intensity, the nucleation rate increases. Moreover, in Dykas cascade, with the increase of back pressure from 48.8 kPa to 73.2 kPa, the maximum wetness decreases from 4.8 % to 2.1 %, whereas with the increase of relative saturation from 0.58 to 0.88, the maximum wetness increases from 2.4 % to 3.6 %. The results obtained in this paper are of significance to accurately analyze the actual situation of non-equilibrium condensation flow of wet steam and to develop methods for reducing wet steam loss in turbine stage.

Effects of rotor squealer tip with non-uniform heights on heat transfer characteristic and flow structure of turbine stage

Squealer tip has a significant influence on both aerodynamic and heat transfer characteristics of the high-pressure turbine. Among the geometric parameters of the squealer, squealer height is one of the essential parameters in the tip design. However, due to the complexity of parameterization and meshing of the squealer, the related research is usually carried out on the squealer with a constant height. In this paper, a parameterization strategy generates squealer of assigned heights at four key positions of the blade, the leading edge-pressure side, the leading edge-suction side, the trailing edge-pressure side, and the trailing edge-suction side. An in-house mesh generation platform (NuFlux) is adopted to automatically generate the structured meshes. The aerothermal performance of a transonic turbine stage is assessed using steady Reynolds-averaged Navier–Stokes simulations with the k−ω shear stress transport model for the turbulence closure. The main purpose is to obtain the squealer tip configuration with the lowest heat transfer coefficient. The results show that non-uniform squealer further reduces the cavity floor heat transfer on the basis of uniform squealer by changing the interaction process between the asymmetric vortex pair (the pressure-side corner vortex and the casing-driven scraping vortex), which provides a valuable reference for the design of the squealer tip of advanced high-pressure turbines.

GTP-24-1666 - Temperature Margin Calculation During Finite Element Creep Simulations (GT2024-121776)

Abstract Creep deformation in turbomachinery applications is a highly non-linear phenomenon where +/- 15°C may halve or double the average rupture life. Even in well-controlled laboratory conditions, this stochastic nature means that identical tests may differ by a factor of two. Analysts using implicit finite element user creep subroutines may not appreciate the uncertainty of their solution, or the design changes required to account for uncertainty in either the boundary conditions or the solution itself. Designing to a maximum strain limit does not consider the sudden acceleration of tertiary creep rates. Applying a time factor may extend the simulation time by multiple factors. This paper presents a methodology where two estimations of creep damage are made in parallel to the creep simulation at actual operating temperatures. These two estimations consider the predicted change in stress relaxation, at higher or lower temperatures, to estimate the temperature change required to reach the onset of creep, at any given node in the model, and at any given time in the analysis. This margin calculation is expanded to consider the uncertainty in creep prediction. A time-based scatter factor is incorporated into the temperature margin calculation to provide a minimum temperature margin that includes model uncertainty. The analyst can also consider the uncertainty of the temperature prediction and boundary conditions to produce a robust creep prediction in a real-world simulation. The methodology is validated through the FEA of example cases and applied to a creep-limited 2nd stage turbine blade.

Impact of Blowing and Density Ratio on the Film Cooling and Heat Transfer in an Aggressive Turbine Center Frame

Abstract It was shown in the previous study that the aft purge flows from the last stage of the high-pressure turbine (HPT) have a significant film cooling potential in the downstream turbine center frame (TCF) (Jagerhofer et al., 2023, “Heat Transfer and Film Cooling in an Aggressive Turbine Center Frame,” ASME J. Turbomach., 145(12), p. 121012). The TCF is a stationary duct that guides the flow from the HPT outlet to the low-pressure turbine (LPT) inlet and is the third most thermally loaded engine component. This article investigates the impact of different purge-to-mainstream blowing and density ratios on the film cooling effectiveness and the heat transfer coefficient in the TCF. The experiments were conducted in a product-representative 1.5-stage HPT-TCF-LPT vane configuration under Mach-similarity in the Transonic Test Turbine Facility (TTTF) at TU Graz. The blowing ratio has been demonstrated to be the dominant parameter for purge film cooling in TCFs since HPT purge flows typically have very low momentum. Even at twice the nominal blowing ratio, no cooling film detachment was observed on the TCF hub or shroud surface. Varying the density ratio in the experimentally possible range delivered no significant differences in the results. With increasing purge blowing ratios, the film cooling effectiveness in the TCF increases as expected, but the heat transfer also intensifies due to the purge injection. The circumferentially averaged film cooling on the hub scales relatively well with an offset version of the well-known Hartnett correlation (Hartnett et al., 1961, “Velocity Distributions, Temperature Distributions, Effectiveness and Heat Transfer for Air Injected Through a Tangential Slot Into a Turbulent Boundary Layer,” ASME J. Heat Transfer, 83(3), pp. 293–305) that takes into account the ingress-induced premixing of the purge flow in the cavities.

Numerical Analysis of A Two-Phase Turbine: A Comparative Study Between Barotropic and Mixture Models

Abstract Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. This paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.

CONTROL OF SHROUD LEAKAGE LOSS AND WINDAGE TORQUE IN A LOW-PRESSURE TURBINE STAGE

Abstract As new aeroengine architectures move to larger diameter fans and rotors, the associated increase in weight will need to be counterbalanced by lighter, more compact, and more efficient low-pressure turbines (LPT). Efficiency gains in LPTs can be achieved by reducing the losses associated with the shroud leakage flows. Flow control studies on the topic have traditionally focused on reducing the mixing loss, which constitutes a considerable proportion of the total loss. Nonetheless, increasing engine speeds are driving additional gains obtained by also targeting the reduction of windage losses. Developing a flow control solution with the dual objective of reducing over-tip cavity mixing and windage losses has not previously been attempted. This is a challenge due to conflicting flow control requirements and geometric constraints. Reducing windage loss generally requires increasing the swirl-ratio of the leakage flow, while reducing mixing loss requires reducing this ratio to match that of the main gas path. The current work proposes a novel flow control solution to successfully achieve this purpose through the emerging technology of additive manufacturing. The successful flow control concept was developed through numerical simulation, printed using an additive manufacturing process, and validated in a purpose-built rig. Experiments and computations were consistent with a cumulative reduction in cavity windage of 16%. The FCC is estimated to increase the mechanical efficiency of the turbine stage in isolation by 1%.

Influence of Dilution and Effusion Flows in Generating Variable Inlet Profiles for a High-Pressure Turbine

Abstract The elevated flow temperatures and pressures exiting gas turbine combustors affect the efficiency and durability of the high-pressure turbine stage. Understanding the effects that result from the upstream dilution and effusion flow interaction in creating the combustor exit profiles is important to advancing gas turbines. Understanding how common combustor features, such as dilution jets and effusion cooling, interact based on computational predictions guided the design of a non-reacting profile simulator capable of producing a wide range of non-uniform temperature profiles representative of those entering high-pressure turbines. The mechanical design of a new simulator device, which will be experimentally tested in the future, is presented in this paper along with computational predictions of flow and thermal fields. The simulator was designed for modular installation into the Steady Thermal Aero Research Turbine (START), which is a continuous-duration, steady-state turbine facility that houses a single-stage test turbine. Features of the simulator included interchangeable liner panels with multiple rows of dilution jets and wall effusion cooling to study various hole diameters and patterns. The dilution jets generate elevated turbulence intensities and tailor the temperature profiles in the radial and circumferential directions. The air mass flow distribution and source flow temperatures are independently controlled. To aid in the simulator design, computational fluid dynamics (CFD) simulations using Reynolds-averaged Navier–Stokes modeling were conducted with a two-level Design of Experiments (DOE) approach to determine a number of engine-representative target profiles with temperature shapes that are mid-radius peaked, outer-diameter peaked, inner-diameter peaked, and uniform. A sensitivity analysis of the CFD DOE results determined which factors significantly affected the profile shape so that the target profiles could be produced. The analysis indicated that the main contributor to the temperature profile shape at near-wall vane radial span locations of 0–15% and 85–100% was the injection temperature of the effusion flow. The main contributor at radial span locations of 15–40% and 60–85% was the injection temperature of the third-row dilution jets, and at the mid-radius location of 40–60% vane radial span, the main contributor was the diameter of the first-row dilution holes.

Variable Geometry Turbine Turbocharger Optimization Using Machine Learning for On-Highway Fuel Cell Applications

<div>Turbocharger design involves adjustment of various geometric parameters to improve the performance and suit mechanical constraints, depending on the application-specific requirements. In designing the turbine stage, these parameters are optimized to maximize durability and efficiencies at the required operating points. For a heavy-duty class eight truck, “road load” and “rated power” are generally considered the two most important operating points. The objective of this article is to improve the efficiencies of these two operating points.</div> <div>The common challenge in the development of a turbine wheel design is the large number and interdependence of parameters to optimize. For example, increasing the blade thickness improves structural strength but reduces the mass flow capacity, thus influencing its performance. It is general practice to optimize the wheel geometry using iterative CFD analysis. However, running simulations for every single change in geometry involves significant computation time and does not guarantee the global optimum.</div> <div>This study proposes a machine learning (ML)-driven optimization process for variable turbine geometry (VTG) wheels with two target operating points. Initial CFD data is collected and used to train/validate a ML model for each operating point. A multi-objective optimization algorithm utilizes these ML models to provide a list of ideal turbine wheel designs, and the best candidates are validated in CFD for accuracy. The results are a balanced maximization in efficiency for both operating points, with an improvement in the pareto front by 1.4% points over CFD optimization alone.</div>

15 years of experience with the Triple Plane Pressure Mode Matching technique

The so-called Triple-Plane-Pressure-Mode-Matching technique (TPP for short) is a method used to isolate and quantify the acoustic part in numerical simulations of turbomachinery. Nowadays, simulations such as Harmonic Balance are commonly applied during the design phase of new turbomachinery components for both aeroacoustic and aeroelastic analyses. The TPP method was first published 20 years ago by Ovenden and Rienstra. The principle is to match the periodic pressure data from three or more neighbouring analysis planes with a subset of acoustic eigenmodes. The original method assumes that the flow in the channel section is potential so that the eigenmodes can be determined analytically. This approach can also be applied in slowly varying ducts. The TPP method is a powerful technique that is used at DLR and MTU Aero Engines. For nearly 15 years, constant joint efforts have been made to improve its applicability in industrial environment. Targeted applications are turbine stages, where the mean flow is complex and vortical wakes contaminate the results. In this paper, the latest developments of the method are presented, including the extension to curved extraction surfaces to enable its application to small blade-row spacing. The utility of the technique is illustrated by an industrial application.

Numerical study on flow control mechanism of endwall fence in a high-lift turbine rotor with open separation

The enhanced cross pressure gradient and the interference effect between secondary flow and separation bubble on the suction side make the refinement of flow organization in the endwall region a key role in improving the performance of low Reynolds number turbine stages. This influence is further amplified in high-lift turbines with open separation. The flow control method of applying endwall fence on a high-lift rotor of a low-speed turbine stage has been numerically studied. By analyzing the transformation of separation bubble on the suction surface and the development of vortices in the endwall region, the flow control mechanism of the endwall fence at low Reynolds numbers is presented. The influence of different fence design parameters on aerodynamic performance has been summarized. The research results indicate that the induced generation of fence vortex can effectively suppress passage vortex. After installing the fence, the intensification of blockage in the endwall region near the leading edge effectively delays the occurrence of laminar separation. Due to the introduction of additional endwall losses, the flow control effect of the fence mainly comes from the suppression of separation. The flow field in the endwall region and flow control effect are significantly affected by the pitchiwse position and height of the fence, while the width of the fence has a slight impact. The flow control effect can be more effectively achieved by designing the height variation of the fence reasonably. In addition, numerical results indicate that the optimized fence all exhibit good control effectiveness under different operating conditions.

High-frequency transverse acoustic interactions between two lean-premixed hydrogen combustors connected with cross-fire and cross-talk sections

Large-scale inter-combustor thermoacoustic interactions occur frequently in modern can-annular gas turbine combustion systems due to the presence of an annular cross-talk section upstream of the first stage turbine stator vanes. Although the whole system's modal dynamics depend on the relative dominance of low-frequency planar or high-frequency transverse acoustic waves, the majority of prior studies have chiefly focused on longitudinal mode instabilities. Motivated by the paucity of detailed information, here we examine high-frequency transverse acoustic interactions between two adjacent lean-premixed hydrogen combustors connected via two different pathways, known as cross-fire (XF) and cross-talk (XT) sections. We observe that the dual-combustor system undergoes high-frequency spinning mode in the clockwise direction, manifested as well-defined limit cycles with peak-to-peak amplitude of around 10 kPa. The transverse pressure oscillations, in contrast to the well-established low-frequency mutual synchronization dynamics, are not fully synchronized even in the presence of cross-talk communication. This situation leads to the formation of two closely-spaced 1T modes at 4.76 and 4.86 kHz in the respective hydrogen combustors, accompanied by the beating of the pressure fluctuations solely in the XF tube section. Remarkably, the pressure waves induced near the XF tube section tend to lag behind the pressure waves spinning in the injector face, demonstrating the existence of the angular shift characteristically connected to the high-frequency transverse combustion dynamics.

High-speed multi-stage gas-steam turbine with flow bleeding in a novel thermodynamic cycle for decarbonizing power generation

In the global pursuit of sustainable energy and reduced carbon footprints, advances in power generation techniques play a crucial role, not only in meeting the ever-increasing energy demands but also in ensuring that environmental standards are maintained and that the health of our planet is prioritized for future generations.In the ongoing quest for sustainable energy solutions, novel high-speed multi-stage gas-steam turbine models were designed to address the challenge of decarbonized power production. The thermodynamic parameters were adopted on the basis of the negative carbon dioxide gas power plant cycle relying on the following main devices, namely: wet combustion chamber, spray-ejector condenser, sewage sludge gasifier and gas-steam turbine. The peculiarities of the present system make the turbine the link of three important devices and its parameters affect the entire thermodynamic cycle. Therefore, it is reasonable to carry out dedicated novel in literature CFD calculations that also take into account the bleeding of the medium for the gasification process.Two distinct turbine models were introduced: a two-stage turbine achieving speeds of 95 000 rpm with an efficiency of more than 80%, and a five-stage turbine reaching 40 000 rpm with an efficiency of less than 70%. A design assumption of a bleed pressure of 100 kPa and a mass flow rate of 0.1 kg/s was adopted for both models. Computational simulations were utilized, and the turbine stages were selected with the aim of reducing energy losses. Through this work, a significant step towards a carbon-negative future using high-speed turbine technologies was demonstrated, laying the groundwork for further advancements in the field.

Effect of Blade Material of Steam Turbine Rotor on Aeroelastic Characteristics

Elements of powerful steam turbines are subjected to significant unsteady loads, in particular the rotor blades of the last stages. These loads, in some cases, can cause self-excited oscillations, which are extremely dangerous and have a negative impact on the efficiency and service life of the blade cascade. Therefore, when designing new or modernizing existing steam turbine stages, it is recommended to study the aeroelastic characteristics of the blades. The conditions for the occurrence of self-excited oscillations are influenced by both the geometric characteristics and the alloy from which the blade is made. To determine the effect of the blade material on the aeroelastic behaviour, a numerical analysis of the aeroelastic characteristics of the last stage blades made of steel and titanium alloy was performed. For the analysis, the method of simultaneous modeling of unsteady gas flow through the blade cascades and elastic vibrations of the blades (coupled problem) was used, which allows obtaining the amplitude-frequency spectrum of the interaction of unsteady loads and blade vibrations. The paper presents the results of numerical analysis for harmonic oscillations with a given amplitude and a given inter-blade phase angle, as well as for the regime of coupled vibration of blades under the action of unsteady aerodynamic forces. The dependences of the aerodamping coefficient on the inter-blade phase angle and the distribution of the coefficient along the blade are presented. The results of modeling the coupled vibration of the blades for the first six natural forms are presented in the form of a time-evolving displacement of the blade peripheral section, as well as forces and moments acting on the peripheral section. The corresponding amplitude-frequency spectra of displacements and loads in the peripheral section are also presented. The analysis of the results showed an insignificant difference in the characteristics of the proposed blade materials. For the first natural form of blade oscillations, the possibility of self-excited oscillations was found, and for the second form, there are conditions for the appearance of stable self-oscillations.

Experimental and simulation study of energy loss mechanism of low pressure ratio radial turbine

Low-pressure ratio conditions are commonly encountered in radial turbines. When operating at low pressure ratio condition, a significant portion of the turbine energy loss occurs as residual velocity loss in the form of swirling flow at the outlet pipe. Typically, this energy can be recovered by the next stage turbine or reduced by the diffuser. However, there is a lack of experimental and simulation studies on the swirling flow at the outlet of turbines. The mechanism governing the changing pattern of swirling flow remains unclear, limiting the effective utilization and reduction of residual velocity loss. This study conducts theoretical and experimental research on turbine outlet swirling flow. Firstly, this paper introduces a novel two-dimensional hot-wire anemometry stepping mechanism for measuring swirling flow at a turbine outlet cross-section. Experimental results demonstrate that the proposed measurement method effectively captures the morphological changes of turbine outlet swirling flow. The results indicate a strong coupling relationship between axial and circumferential velocity. Subsequently, to elucidate the reasons for the coupling of velocity in two directions and the development of swirling flow in the outlet pipeline, simulations of turbine performance under different velocity ratio conditions were conducted. Results show that under a wide range of velocity ratios, not only does the direction of the turbine outlet swirling flow change, but it also leads to the swirl number exceeding the critical swirl ratio under high velocity ratio conditions, resulting in the formation of a central recirculation zone (CRZ) at the pipe outlet. The main cause of the strong coupling effect between velocities in two directions is attributed to the increased swirl intensity leading to enhanced adverse pressure gradients at the core of the vortex. Lastly, a model describing the variation of VGT turbine outlet swirling flow is established, indicating a linear relationship between the swirl number and the velocity ratio, with a steeper change as the pressure ratio decreases.

A novel wide flow matching approach of hydrogen-powered F-class gas turbine based on multistage installation angle

To achieve excellent power performance of F-class gas turbine when using pure H2 or H2-rich fuel, this work develops a novel and flexible flow matching approach by modifying the turbine multistage installation angle, with obvious features of easy implementation and low cost. An accurate thermodynamic model of heavy-duty gas turbine considering turbine-stage cooling is established and verified by the actual operation data from Ban-Shan power plant, and to investigate variable condition property and emission characteristic of gas turbine with natural gas and H2-rich fuel. Faced with the inefficiency and narrow working area caused by the flow mismatch between 18-stage compressor and 3-stage turbine when natural gas is switched to H2-rich fuel, the scheme of modifying the installation angles of multistage rotary blade and static blade is proposed. By calculating the pressure and temperature at each turbine stage, the gas turbine power, efficiency, Mach number and NOx emission with different H2 concentration are predicted. Results show that, as the H2 concentration increases, the fuel volume flow required to reach the same turbine inlet temperature increases.When H2-rich fuel increases the turbine inlet volume flow by 3.23 %, the cooling effect significantly decreases, and the turbine outlet temperature rises by about 13.60 K, which deviates from the appropriate operating point. The most serious is the phenomenon of over Mach number and airflow blocking at the outlet of the 2-stage and 3-stage turbine static blades. The installation angle variation increases with the increase of H2, and the higher the stage, the bigger the angle change. The gas turbine can be realized the wide flow matching feature corresponding to the installation angle variation of 0.19°/-0.41°, 0.38°/-0.48°, and 0.53°/-0.94°, respectively for all stages static/rotary blades. After re-matching, the maximum fluctuation of rated power and efficiency are 1.5 % and 1.7 %, and the NOx emission will reach the maximum value of 14.3 ppm with 70 % H2. Research work will provide a novel and feasible retrofit scheme for the heavy-duty gas turbine using clean and low-carbon fuel to widen flow matching scenario.

Assessment of a solar-powered trigeneration plant integrated with thermal energy storage using phase change materials

This study presents a comprehensive thermodynamic assessment of a trigeneration plant producing electricity, fresh water through multi-effect desalination (MED), and cooling through an absorption refrigeration cycle. The MED and absorption refrigeration systems utilize the rejected heat from the power cycle, driven by concentrated solar power (CSP). Situated in Qatar, the present system leverages the abundant solar irradiance to optimize the efficiency of electricity generation, water desalination, and cooling. The design features parabolic trough collectors with synthetic oil as the heat transfer fluid, direct thermal storage, and a Rankine steam turbine cycle with three turbine stages. The system also incorporates phase change materials (PCMs) based thermal energy storage (TES) to improve the system performance and offset the mismatch between demand and supply. The present system evaluation is based on energy and exergy analyses, while the Aspen Plus is used to simulate the power production and desalination operations, providing detailed insights into its efficiency and potential for large-scale implementation. The proposed system operates with an energy efficiency of 56.72 % and an exergy efficiency of 31.24 %, respectively.