Adiabatic Efficiency Research Articles

Performance sensitivity analysis and aerodynamic optimization of compressor cascades by a turbulence adjoint method

Sensitivity, which is useful for evaluating the contributions of input variations to output changes, favors designers exploiting the most sensitive design parameters and completing design optimization in aerospace. This study introduces the turbulence adjoint method due to its low computational cost in calculating sensitivities with high accuracy and then solves the adjoint partial differential equations with respect to both the Reynolds-averaged Navier–Stokes and turbulence model equations with the assistance of an automatic differentiation tool. By utilizing the turbulence adjoint method, the sensitivities of aerodynamic performance to the blade profile modifications of two-dimensional and three-dimensional compressor cascades are calculated, allowing for the investigations of the impact of geometric variations on the changes in the flow field. Ultimately, aerodynamic optimization of the compressor cascades is conducted. After optimization, the adiabatic efficiency of the two-dimensional cascade increases by 3.11%, and it increases by 1.15% for the three-dimensional cascade. The variations in flow fields of both the original and optimized cascades are illustrated to discover the origins of performance improvements. The changes in blade profile are almost consistent with those forecasted from sensitivity analysis, demonstrating the potential superiority of the adjoint method for aerodynamic design.

Semi-empirical model of the twin-screw refrigeration compressor with capacity control devices

Adopting twin-screw refrigeration compressors with capacity control devices has become the dominant trend to meet varying cooling demands. To analyze the compressor performance with different capacity control methods and further explore the potential, a semi-empirical model with 16 characteristic parameters is proposed. Detailed working processes under the part-load condition (PC) are considered and the corresponding calculations, including pressure loss, power loss, and leakage are innovatively refined. Subsequently, a prototype experiment was carried out for parameters identification and model validation. A good agreement between the experimental and simulated values is attained, with average relative errors of 3.46 % and 1.15 % for shaft power and mass flow rate under the variable frequency condition (VFC) and 3.18 % and 4.63 % under the PC. Thermodynamic simulation results indicate that both shaft power and mass flow rate are linearly correlated with frequency and the efficiencies are nearly stable over the whole interval. However, as the load decreases, the performance decays significantly and the most remarkable change occurs at a position of between 0.9 and 1. The volumetric and adiabatic efficiencies of the VFC are 3.65 and 2.26 times higher than that of the PC when the mass flow rate reaches the lower limit.

Design, optimization, and performance analysis of a subsonic high-through flow turbine

This paper presents the design method and numerical analysis results of a two-stage high-through flow (HTF) high-pressure turbine. Compared to conventional design principles, the HTF turbine proposed in this study is a kind of high flow coefficient turbine. This design scheme enables the turbine to effectively increase the output power and thrust while maintaining the same windward area. At the design speed, the pressure ratio of the HTF turbine is 3.8, with an adiabatic efficiency of 91.46%. The flow coefficients of the first and second stage are 0.76 and 0.86, respectively, and the loading coefficients are 2.55 and 1.47. Detailed design parameters, flow characteristics, and aerodynamic performance are presented in this paper. Based on the preliminary design result, the second stage turbine was optimized for a wide range of operating conditions. The computational fluid dynamics simulation results show that compared with the traditional turbine, the loading form of the HTF turbine changes from aft-loaded to front-loaded. In addition, there is a certain increase in tip leakage of the turbine. This study achieves high efficiency, while increasing the turbine flow rate, and provides a corresponding reference for the design method of improving turbine flow capacity.

Enhanced electrocaloric effect in (Bi0.5Na0.5)TiO3-6BaTiO3 based relaxor ferroelectric nanocomposites by regulating Joule heating

Recently, electrocaloric effect (ECE)-based cooling technology has attracted a great deal of research attention. With a relatively high energy conversion efficiency (∼70 %) and no generating greenhouse gases, ECE-based cooling technology is suitable for use in the next generation of solid-state cooling devices. In this investigation, the PMMA layer was coated on the surface of (Bi0.5Na0.5)TiO3-6BaTiO3-1.5 %BiCoO3 (BNBT-BCO) nanofillers to reduce the Joule heat of BNBT-BCO/terpolymer (P(VDF-TrFE-CFE)) nanocomposite. From the ECE measurement result, the adiabatic temperature change (ΔT) of the BNBT-BCO@P/T-15 nanocomposite film reached 10.33 °C under 90 MV/m, which is 25 % higher than that of the BNBT-BCO/T-15 nanocomposite film (no PMMA coating, ∼8.29 °C) under the same electric field. In addition, the ΔT of the BNBT-BCO@P/T-15 nanocomposite film reached 17.52 °C under 150 MV/m at room temperature. This value is approximately 60 % higher than that of the pristine terpolymer films (ΔT ∼ 10.84 °C) and 17.4 % higher than that of BNBT-BCO@P/T-20 nanocomposite film (ΔT ∼ 14.92 °C). This work creates a new approach to using the surface coating on ceramic nanoparticles to reduce the Joule heat of the nanocomposites and improving the adiabatic temperature change (ΔT) and efficiency of ECE devices.

Prescreening surrogate-model-assisted multi-objective aerodynamic optimization design of highly loaded axial compressor in heavy-duty gas turbine

To address the challenges of numerous design variables and high evaluation costs in the aerodynamic optimization of advanced highly-loaded axial compressors, this paper presents an axial compressor aerodynamic optimization platform based on directly manipulated free-form deformation (DFFD) parameterization method, a data-driven multi-objective differential evolution optimizer, and computational fluid dynamics. The DFFD method allows for direct geometric manipulation of the target compressor, enabling efficient parameterization of the blades and flow path and reducing the number of design variables. A prescreening surrogate-model-assisted multi-objective differential evolution (Pre-MODE) optimizer is developed to obtain competitive solutions within a limited number of iterations. The surrogate model in Pre-MODE conducts real evaluations only on selected individuals in each generation, thereby reduce evaluation costs while ensuring prediction accuracy. Additionally, a parallel task management system is integrated to improve optimization efficiency. To verify the effectiveness of the optimization platform, a 1.5-stage highly-loaded compressor is aerodynamically optimized. After optimization, the adiabatic efficiency at the design point and the surge margin are increased by 2.42% and 9.04%, respectively. These results confirm the effectiveness and speed of the aerodynamic optimization platform, promoting the establishment of an integrated optimization design system for axial compressors.

Theoretical and Experimental Research on Thermal Dynamic Characteristics of Single-Screw Compressor with a New Composite SLIDE Valve

Based on the single-screw compressor (SSC) structure, a new type of composite slide valve (CSV) has been proposed and designed, featuring internal volume ratios of 2.8, 3.9, and 5.6 and operating under a partial load of 35%. The theoretical model describing the dynamic features and thermodynamic performance of the SSC with CSV has also been built. The pressure ratio of the experimental system can be adjusted from 3.3 to 7.8, and the experimental results demonstrate the CSV’s effective performance. The deviations between the calculated and measured results for volume ratio and input power are 3.33–9.08% and 0.32–8.03%, and the deviations for heating capacity and adiabatic efficiency range from 0.92–8.73% to 2.09–9.67%, respectively. The introduction of the CSV offers a novel approach to enhancing SSC efficiency. Both the theoretical and experimental findings lay a foundation for future optimization and design improvements in variable load and internal volumetric ratio single-screw compressors.

Experimental Analysis of Twin Screw Compressor's Energetic Efficiency Depending on Volume Ratio

The current paper presents the results of the experimental analysis to assess and optimize the twin-screw compressor’s efficiency by varying the volume ratio. The experimental tests are conducted on the compressor's test bench, with a dedicated automation system inside the control console. The control and monitoring software allows parameter recording for subsequent visualization, data curation, and post-processing. The evaluation of screw compressor's performance requires a simultaneous analysis of the thermodynamic and flow processes, both of which depend on the compressor’s geometry. The obtained volumetric and adiabatic efficiencies are good, with values over 0.88 and 0.69, respectively.

A new CO2 refrigeration system with two-phase ejector and parallel compression for supermarkets

This study explores the integration of parallel compression and a two-phase ejector in transcritical CO2 refrigeration systems, aiming to improve efficiency and performance. This innovative approach bridges the gap between conventional approaches and explores new energy-saving potential. The study uses thermodynamic modeling, mathematical simulation, and in-depth analysis to look at energy and exergy performance in a new configuration for applications in the retail sector at medium evaporation temperatures. The work investigates thermodynamic phenomena in a novel cycle with steady-state conditions, low pressure differentials, and adiabatic efficiency. The model is validated against experimental and theoretical published data, revealing component-specific exergy destruction and key parameters. The novel cycle efficiently extracts heat at higher temperatures, outperforming conventional and parallel cycles. Exergetic efficiency surpasses the standard cycle, with gas cooler pressure and temperature dependence enhancing efficiency by 40%–45%. The distribution of exergy destruction percentages reveals efficiency determinants, emphasizing heat exchange optimization and ejector responsiveness in energy dissipation dynamics. The study investigates the coefficient of performance (COP) dependence on gas cooler pressure and temperature, revealing superior performance compared to conventional cycles. COP increases by 50% at 80 bars, indicating enhanced efficiency. The new cycle offers exceptional efficiency gains, with a COP enhancement of over 75% for evaporator temperature transitions. Comparative analysis shows a COP superiority of up to 53% for lower evaporator temperatures and 20% for higher evaporator temperatures, demonstrating substantial energy savings and improved performance across various operating conditions.

Rotor profile improvement by optimizing meshing curve for helical roots blowers in HFCV application

This paper introduced a novel design and optimization method of the Roots profile to enhance the performance of helical Roots blowers in Hydrogen Fuel Cell Vehicle applications. The proposed profile was generated based on defined meshing curves, and thus the shape of meshing curves can be explicitly optimized. First, the mathematical models for Roots profile generation based on meshing curves were presented. Next, the influence of the shape of meshing curves on the geometric performance of Roots rotors was investigated, and the meshing curve was further optimized using a genetic algorithm. Finally, the CFD method was employed to identify the specific performance enhancement brought by the optimized Roots profile. Results showed that the proposed profile design method could flexibly adjust the shape of meshing curves so as to intuitively control the spatial leakage channels formed by helical rotors. The optimized profile boosted the volumetric and adiabatic efficiency of the Roots blower up to 2.87%, and 1.89%, respectively, compared to the original one. The leakage analysis indicated that the performance improvement was attributed to the reduction of the leakage rate caused by the blow-hole and contact line. The conclusions obtained could effectively support the development of high-efficiency helical Roots blowers.

Non-uniform flow characteristics and rotating instability of a transonic high-pressure compressor rotor with cavity bleed

The presence of bleed in an aero engine’s compressor can significantly impact its flow characteristics and contribute to rotating instability. This study focuses on the impact of a typical cavity bleed structure on the internal flow characteristics of a compressor, specifically its circumferential non-uniformity and aerodynamic stability. A numerical simulation involving multiple flow passages was conducted on the transonic high-pressure rotor of the E3 compressor, considering its typical bleed structure. The study delves deep into the non-uniform flow characteristics and the mechanisms behind their generation in the compressor flow field. Furthermore, the influence of bleed on the rotating instability of the compressor is explored by comparing changes in compressor instability and adiabatic efficiency under uniform and non-uniform flow field conditions. The findings indicate that the axial position of the cavity bleed structure plays a crucial role in influencing key parameters such as rotor stall margin, peak efficiency, and total pressure ratio under near-stall conditions. The circumferential non-uniformity, resulting from the presence of the cavity bleed, intensifies with higher bleed air flow rates. For the upstream bleed configuration applied to the rotor, with a total bleed rate of 5%, the maximum variation in absolute flow angle at the inlet of different rotor channels can reach up to 1°. Additionally, the maximum difference in inlet flow coefficient can reach 0.0392. These findings demonstrate that the non-uniformity caused by the typical bleed structure leads to a loss in stall margin for the rotor when compared to a uniform flow field scheme.

Techno-economic analysis on the balance of plant (BOP) equipment due to switching fuel from natural gas to hydrogen in gas turbine power plants

<abstract> <p>The concerns over greenhouse gas emissions, environmental impacts, climate change, and sustainability continue to grow. As a result of countermeasures, many modern gas turbine power plants and combined cycle power plants are considering to use hydrogen as a clean fuel alternative to fossil fuels in the power plant industry. We assessed the implications of such transition from natural gas to hydrogen as fuel in a gas turbine power plant's balance of plant (BOP) equipment. Using the DWSIM process simulation software and the methodology of compression power changes against different gas compositions, the impact of blending hydrogen with natural gas on temperature differentials, energy consumption, adiabatic efficiency, compression power, and economic implications in gas turbine power plants were examined in this paper. We discovered, through analysis, that there was not a noticeable boost in compression power or energy consumption when 50% hydrogen and 50% natural gas were blended. Similarly, there was no discernible difference in temperature differentials or adiabatic efficiency when 30% hydrogen and 70% natural gas were blended. Moreover, mixing 50% hydrogen and 50% natural gas did not result in a noticeable cost climb. In addition, the techno-economic analysis presented in this paper offered valuable insights for power plant engineers, power generation companies, investors in energy sectors, and policymakers, highlighting the nature of the fuel shift and its implications on the economy and technology.</p> </abstract>

Comparative analysis of turbulence model influence in numerical simulation of an experimental radial compressor stage

The accuracy of a CFD model of a turbo-machine might depend on a number of factors: turbulence model, quality of the mesh model, boundary conditions, solver settings, consideration of secondary geometric factors, etc. The purpose of this work is to develop practical recommendations for CFD calculations of centrifugal compressors based on the validation of a model of NASA High Efficiency Centrifugal Compressor experimental radial compressor stage. Results of a grid independence test are presented, and the optimal grid size for the High Efficiency Centrifugal Compressor stage is identified as comprising 3 million elements. CFD-calculations of an experimental stage were performed with different turbulence models. The obtained data was compared with the NASA experimental data considering integral (total pressure ratio, mass flow rate, adiabatic efficiency) and differential parameters (static pressure distribution downstream the vaned diffuser). The required CFD computational time for different turbulence models was calculated. Based on the results of this research, recommendations were formulated for the application of SST, k–ε, BSL EARSM and GEKO turbulence models for numerical modeling of centrifugal compressors.

Equivalent diffusion ratio distribution in the UGT15000 low pressure compressor

With spatial and temporal periodicity approach the results of steady state CFD simulation of compressible air flow in each blade-to-blade row of low pressure compressor (LPC) of the UGT15000 gas turbine engine (Ukrainian SSR constr. and prod.) are presented. Near the nominal rotation speed compressor map and adiabatic efficiency of each stage and the flow angles at leading and trailing blade edges are predicted and calculated. At the average radius stage flow and stage load coefficients are determined. It has been established that the reason of the low efficiency of the last stage is associated with the low stage reaction (≈0.5) leading to high airflow swirling at outlet. For LPC optimization a calculation of the radial distributions of the equivalent diffuser coefficient was performed. It is shown that the greatest total pressure losses are in the stator rows of stages 9, 8, 5 and in the rotor rows of stage 9. High losses are also shown on the upper half of the 4th, 3rd, 2nd stator blades and the lower half of the 1st rotor blades. The identified potential for increasing the efficiency of the LPC is up to 2% without significant construction changes.

Three-dimensional optimization of squealer-tip for a transonic axial-flow compressor rotor blade

This research represents an innovative method for geometry generation of the squealer-tip in axial compressor rotors and its exploit in a numerical optimization process to obtain a better stage performance. For this purpose, the NASA Rotor-67 transonic compressor rotor blade is used as a test case to study the aerodynamic performance using computational fluid dynamics. The validation was performed for the characteristic map at the design speed and the comparison with the experimental results indicates excellent matching and high adaptability of the numerical method. An ingenious method of producing squealer tip for an axial compressor rotary blade is presented in this article, which is capable for locally shaping both suction and pressure surface geometry at a desired spanwise location simultaneously, while keeping the tip clearance at its value of the baseline NASA Rotor-67 geometry. In this method, control points are used to produce the starting spanwise location of the squealer, and modify the depth of the squealer geometry. The L-27 orthogonal array of the Taguchi method as the Design of Experiment (DOE) has been used to investigate the sensitivity of the aerodynamic results in three performance points of the choke, design and near stall regions, in relation to the design variables of the squealer. The generated database in the sensitivity analysis was used to train artificial neural networks to replace the CFD solutions with overwhelming run time. By coupling the genetic algorithm to the aforementioned neural networks and by applying penalties to maintain the minimum performance of the Rotor-67, enhancement of total pressure ratio, adiabatic efficiency, mass flow rate and even the surge margin was achieved. The main effect of the squealer is to modify the shape of blade tip vortices, and by more dissipation of energy in blade tip area and reduced equivalent flow area in this region, finally results in improved overall mass flow rate, total pressure ratio, adiabatic efficiency and surge margin by 0.58 %, 0.36 %, 0.19 % and 4.81 % respectively, at design point.

Investigation of transitional flow in a transonic compressor rotor with hub leakage using large eddy simulation

The hub leakage flow has been acknowledged as an important factor for performance deficiency of axial-flow compressors. Meanwhile, the laminar-turbulent transition in compressors is highly sensitive to the upstream flow state and significantly affects the flow loss. In the present work, quasi-wall-resolved large eddy simulation of a transonic axial-flow compressor rotor at the near-peak-efficiency point is carried out to investigate the effects of hub leakage as well as its absolute tangential velocity on the compressor performance and the laminar-turbulent transition in the blade passage. It is confirmed that the hub leakage with an absolute tangential velocity of 0.5 wheel speed can result in the near-hub total pressure deficit. With the hub leakage taken into account, the predicted total pressure ratio and adiabatic efficiency agree well with the experimental data. The simulation results indicate that increasing the absolute tangential velocity of hub leakage would intensify the near-hub vortices, elevate the endwall turbulence level, increase the near-hub flow loss, and cause a remarkable total pressure ratio drop. This work promotes the understanding of complex flow mechanisms in axial-flow compressors in the presence of hub leakage.

Performance improvement of twin screw refrigeration compressors for chillers by modifying the suction arrangement

To improve the efficiency of the twin-screw refrigeration compressor at a high speed of about 3000 rpm, the suction arrangement was investigated in this paper. Several simplified CFD models of a twin-screw refrigeration compressor for chillers were established to parametrically analyze the influence of the suction delay, rotor wrap angle, and suction bearing distance. The parametric studies showed that the volumetric efficiency could be improved by 3 % by a suction delay of 18°, and more volumetric efficiency could be improved by shortening the length of it. The optimal delay angle was found to be linear with the rotational speed. Increasing the wrap angle from 300° to 330°, the volumetric efficiency decreased by 2–3 %, and the adiabatic efficiency increased by about 0.2 %. By increasing the distance between the suction bearings and the rotor end face from 5 mm to 80 mm, the isentropic efficiency increases by about 1.4 %. Based on the parametric studies, two modified machines were built and tested by experiments. Experimental results showed that the volumetric efficiency of machines #1 and #2 increased by 1.5 % at 3000 rpm. The isentropic efficiency of machine #2 increased by 0.78 % at 3000 rpm and 1.27 % at 3300 rpm.

Theoretical, CFD modelling and experimental investigation of a four-intersecting-vane rotary expander

Expansion devices significantly impact the performance of the Vapor Compression Refrigeration system and Organic Rankine Cycles. Its improvement has been identified as one of the most crucial parts of future studies. The experiments were carried out using an improved experimental rig with direct coupling of the prototype and the dynamometer. This is done to correct any misalignments caused by external forces. The internal pressure in the working chambers was measured using six pressure transducers at various locations on the expander. A three-dimensional computational fluid dynamics and theoretical model was developed to investigate the effect of losses and inherent physical processes on the prototype. The actual geometry of the stator is taken in the computational fluid dynamics model. Conversely, employing the equation for an irregular stator shape in the theoretical model is difficult. Therefore, a circular stator is considered. The experimental results were used to validate the developed models. The prototype was tested up to 1550 rpm rotating speed, 5 bar (abs) suction pressure, and 1 bar discharge pressure (abs). The computational fluid dynamics and theoretical model results showed that though the volumetric and adiabatic efficiency was generally overpredicted, the trends were very closely predicted. The computational fluid dynamics and the theoretical model could predict the volumetric and adiabatic efficiency with a variance of <19.5% and 14.7%, respectively, for most of the experimental data points.

Temperature measurement at turbine outlet achieved by a sensing net and infrared thermometry method

The measurement of turbine outlet temperature is challenging because of an intense swirl and high speed at this position. However, accurate measurement of the turbine outlet temperature is fundamental for characterizing the turbine performance. The paper proposed an infrared thermometry method based on the temperature sensing net (TSN) to measure the temperature distribution at the turbine outlet. First, this article describes the design and operation of the measurement procedure through infrared technology to accomplish this difficult task. Then, the temperature and velocity distribution at the turbine outlet and the adiabatic efficiency of the turbine are obtained using the CFD (Computational Fluid Dynamics) method to verify the feasibility of the proposed scheme. And the CHT (Conjugate Heat Transfer) simulation results for the TSN show that the incoming flow mass rate has a great influence on TSN temperature. In contrast, the influence of the incoming flow temperature gradient on it is almost negligible. Moreover, the fluid flow behavior and static temperature distribution around the temperature-sensing wire (TSW) at different Mach numbers are analyzed, and the heat transfer mechanism between the TSW and the fluid is revealed. The results show that the temperature of the TSN is lower than that of the incoming flow, but the distribution law is similar. The main factor affecting the temperature difference between the TSW and the fluid is the incoming flow velocity.

New Insights into Flow for a Low-Bypass-Ratio Transonic Fan with Optimized Rotor

In this paper, a three-dimensional aerodynamics optimization system is built and applied to optimize a rotor blade to balance the conflicts between stall margin, total pressure ratio, adiabatic efficiency, and mass flow rate for the high-loading and transonic-flow fan. A novel flow diagnostic method based on vorticity dynamics theory is utilized to analyze the reasons for the improvement in aerodynamic performance in the optimized transonic fan. In the established aerodynamic optimization method, use the blade profile camber line curvature and its leading edge metal angle as the optimization variables, which are optimized by modifying the coordinates of their control points and introducing a genetic algorithm. Finally, the vorticity dynamics parameters, such as the boundary vorticity flux (BVF), azimuthal vorticity and skin-friction lines are used to diagnose the key flow features in the optimized and baseline fan passage. The results indicate that, by controlling skillfully the blade camber line curvature in the optimization improves the aerodynamic performance of the fan stage, increasing the total pressure ratio by 1.90% while increasing the mass flow rate and adiabatic efficiency by 5.82% and 4.45%, respectively. The formulas from the vorticity dynamics diagnosis method indicate a close link between the aerodynamic performance and vorticity dynamic parameters for the axial fan/compressor passage flow, and that both azimuthal vorticity and boundary vorticity flux have significant influence on fan stage performance. Moreover, the boundary layer separation flow on the rotor blade surface is accompanied by a spike of entropy and static pressure, and their derivative/gradient also suffer drastic changes under the effect of shock waves. Detailed flow information can be obtained about the on-wall with high accuracy based on the vorticity dynamics diagnosis method, which provides researchers with a novel method for the turbomachinery aerodynamic design and analysis in the aero-engine engineering development field.

Design and analysis of a novel liquefied air energy storage system coupled with coal-fired power unit

With its large scale and high flexibility, liquefied air energy storage is very suitable for integrated operation with existing power generation systems to improve the regulation ability of the grid. A novel liquified air energy storage system coupled with coal-fired power unit for heat exchange through the water/steam and the compression/expansion air is proposed. The thermodynamic model of a novel liquified air energy storage system is established with a 307 MW coal-fired power unit as the coupling object. And the parameters design and performance analysis of the coupling system are carried out. The results show that the efficiency of the system can reach 51.64 %. At this time, the corresponding energy storage/release pressure is 18/7.2 MPa. The highest return on investment of the system can reach 19.59 %, and the shortest dynamic payback period can reach 4.73 years. The sensitivity analysis shows that decreasing the heat transfer end difference of the regenerator and increasing the adiabatic efficiency of the compressor are conducive to reducing the exergosy destruction of equipment and improving the efficiency of the system. It is beneficial to improve the economic performance of the system to increase the difference between peak and valley electricity prices and the amount of peak regulation subsidy.