Adiabatic Efficiency Research Articles

케이싱 그루브가 장착된 천음속 축류압축기의 작동 안정성 향상을 위한 수치최적화

Optimization using a hybrid multi-objective evolutionary algorithm coupled with response surface approximation has been performed to improve the performance of a transonic axial compressor with circumferential casing grooves. In order to optimize the operating stability and peak adiabatic efficiency of the compressor with circumferential casing grooves, tip clearance, angle distribution at blade tip and the depth of the circumferential casing grooves are selected as design variables. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume approximations. The trade-off between two objectives with the interaction of blade and casing treatment is determined and discussed with respect to the representative clusters in the Pareto-optimal solutions compared to the axial compressor without the casing treatment.

An aerodynamic design and numerical investigation of transonic centrifugal compressor stage

In the present paper, the design of a transonic centrifugal compressor stage with the inlet relative Mach number about 1.3 and detailed flow field investigation by three-dimensional CFD are described. Firstly the CFD program was validated by an experimental case. Then the preliminary aerodynamic design of stage completed through in-house one-dimensional code. Three types of impellers and two sets of stages were computed and analyzed. It can be found that the swept shape of leading edge has prominent influence on the performance and can enlarge the flow range. Similarly, the performance of the stage with swept impeller is better than others. The total pressure ratio and adiabatic efficiency of final geometry achieve 7:1 and 80% respectively. The vane diffuser with same airfoils along span increases attack angle at higher span, and the local flow structure and performance is deteriorated.

Multiobjective Optimization of Circumferential Casing Grooves for a Transonic Axial Compressor

R ECENTLY, casing treatments using grooves or slots have been applied to axial compressors to prevent surge and enhance stall margin (SM). However, this is accompanied by a loss near the blade tip region, which leads to a decrease in efficiency of the axial compressor. Therefore, a systematic design of the casing treatment using multiobjective optimization techniques in conjunction with a flow analysis using three-dimensional Reynolds-averaged Navier– Stokes equations (RANS) was used to investigate a compromise between the SM and the efficiency of the compressor. Various types of grooves have been suggested by many researchers, and it has been reported that using grooves increases SM by delaying stall. Huang et al. [1] studied the effects of the configuration, width, and depth of circumferential groove casing treatment on SMby numerical analysis, and suggested that the stall mechanism was substantially influenced by tip clearance.Muller et al. [2] studied the effects of the number and depth of the grooves on SM by threedimensional numerical analysis. Houghton and Day [3] examined the effect of grooves on rotor outflow blockage, and the near casing flowfield was studied using experimental and computational methods. Many engineering designs involve multiple disciplines and simultaneous optimization of multiple objectives related to each discipline. These design problems, usually known as multiobjective problems, require simultaneous consideration of all objective functions to optimize the system. The nondominated sorting genetic algorithm (NSGA-2) by Deb [4] generates a Pareto-optimal solution using an evolutionary algorithm. Shape optimization of a hydraulic turbine diffuser was performed with multiple objectives by Marjavaara et al. [5]. Kim et al. [6] reported a multiobjective optimization of a centrifugal compressor impeller with four design variables that defined the impeller hub and shroud contours in meridian terms. Samad and Kim [7] reviewed the performance of the surrogate models applied to turbomachinery design optimization, and introducedmulti and single-objective optimization techniques in conjunction with three-dimensional RANS analysis. In this study, based on previous work [8] for a single-objective optimization, a hybridmultiobjective evolutionary algorithm (hybrid MOEA) [9] coupledwith the Kriging (KRG)model [10] was applied to obtain a global Pareto-optimal front for the design of circumferential casing grooves in an axial compressor with NASARotor 37 [11]. To the best of the authors’ knowledge, no previous study has reported on the optimization of the design of circumferential casing grooves. The present multiobjective optimization was motivated to provide an efficient tool for the design of an axial compressor with circumferential casing groove treatment, and it is expected for designers to meet their design requirements with regard to the SM and adiabatic efficiency from the Pareto-optimal designs (PODs) obtained in this work. Numerical solutions at the selected design points were obtained by three-dimensional RANS analysis. The shape of the grooves was optimized by considering width and depth as designvariables in order to improve the SM and the peak adiabatic efficiency. The tradeoff between these two competing objective functions is explored and discussed with respect to the design variables.

Investigation of a wet ethanol operated HCCI engine based on first and second law analyses

Abstract In this paper, a conceptual wet ethanol operated homogeneous charge compression ignition (HCCI) engine is proposed to shift the energy balance in favor of ethanol. The investigated option, HCCI engine is a relatively new type of engine that has some fundamental differences with respect to other prime movers. Combined first and second law of thermodynamic approach is applied for a HCCI engine operating on wet ethanol and computational analysis is performed to investigate the effects of turbocharger compressor ratio, ambient temperature, and compressor adiabatic efficiency on first law efficiency, second law efficiency, and exergy destruction in each component. First law and second law efficiencies are found to be an increasing function of the turbocharger pressure ratio, while they are found to be a decreasing function of the ambient temperature. The effect of turbocharger pressure ratio on exergy destruction is found to be more significant than compressor efficiency and ambient temperature. Exergy analysis indicates that maximum exergy is destroyed in HCCI engine which represents about 90.09% of the total exergy destruction in the overall system. Around 4.39% exergy is destroyed by the process of heat transfer in fuel vaporizer and heat exchanger. Catalytic converter contributes about 4.08% of the total exergy destruction. This will provide some original information on the role of operating variables and will be quite useful in obtaining the optimum design of ethanol fuelled HCCI engines.

Preliminary experimental study of single screw expander prototype

Abstract Efficient heat conversion of low temperature heat source is a key problem for energy saving, especially in the fields of waste heat recovery and renewable energy utilization. At present, technical bottleneck for low temperature thermal power is lack of suitable prime mover. As the core component of general machinery, single screw has many good features, including balanced loading of the main screw, low leakage, low noise, low vibration and long working life, etc. If single screw technology is applied to the field of expander, more efficient prime mover would be possibly obtained, compared with pistol expander, scroll expander and twin screw expander, and so on. In order to verify the performance of the prototype, the function experiment was made. In this paper, compressed air was used as working fluid and performance test for the prototype was finished at conditions including different intake flow, different humidity, constant torque, and constant rotational speed. From the experimental data, it is shown that the power output is 5 kW, exhaust temperature is −45 °C, difference between the import and export is about 62 °C, in the conditions of inlet pressure at 0.6 MPa and rotational speed 2850 rpm. The test results also show that the single screw expander has good part load characteristics. From the analysis of experimental data, we found that adiabatic efficiency of the prototype is not so high probably because of poor lubrication. The lubrication problem will be considered in the next work.

Multi-Objective Aerodynamic Optimization Design Method of Compressor Rotor Based on Isight

In order to achieving the multi-objective optimization of the compressor rotor blade, a hybrid optimization design algorithm was proposed. The algorithm included three parts: the design of experiment technology was applied to reduce the dimensions of the design variables; the response surface model was established according to the simulation data of the experiment design; the Non-Dominated Sorting in Genetic Algorithm was applied to acquire the multi-objective optimization solutions. In this study, NASA rotor37 was optimized for the maximization of the pressure ratio and adiabatic efficiency using the hybrid optimization algorithm. The result demonstrates that the optimization design method was effectively feasible.

B213 ブレイトンサイクルにおける作動流体選定に関する一考察(OS10 外燃機関・廃熱利用)

This paper proposes working fluids selection for Brayton cycle of closed gas turbine driven by heat source with small temperature difference. The heat source temperatures are 80℃ to 300℃ and 40℃ for higher and lower, respectively. Working fluids are natural substances and these are chosen from the reason that these critical temperatures are lower than 40℃. The selected working fluids are 17 fluids. Pressure determination has two optimization methods, the one employs the maximum thermal efficiency as objective function, and the other employs the maximum net work. The effects of the heat source temperature and the adiabatic efficiencies of compression and expansion processes are discussed. As a result, the substances, which have higher critical temperatures, are adequate to Brayton cycle driven with low temperature heat source. Nitrous oxide and Carbon dioxide are selected from the viewpoint of cycle performance.

Thermodynamic Analysis of Part-Flow Cycle Supercritical CO2 Gas Turbines

Cycle characteristics of closed gas turbines using supercritical carbon dioxide as a working fluid are investigated. It is found that an anomalous behavior of the physical properties of CO2 at the pseudocritical point may limit the heat exchange rate of a regenerative heat exchanger due to the presence of a pinch point inside the regenerative heat exchanger. Taking such a pinch problem into consideration, the cycle efficiency of the Brayton cycle is assessed. Its value is found to be limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative, a part-flow cycle is investigated and its operable range has been identified. It is revealed that the part-flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20 MPa and 800 K. Optimal combination of turbine expansion ratio and a part-flow ratio is 2.5 and 0.68, respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency.

Aerodynamic sweeping study and design for transonic compressor rotor blades

The objective of the present paper is to study the sweep effect on the blade design performance of a transonic compressor rotor. The baseline to be modified and swept is a designed well efficient transonic single rotor compressor. The first part of the present study is concerning the sweep effect with straight leading edge. In this case fixing the hub section the swept blade is formed by tilting the leading edge with whole blade forwards and backwards axially. The second part is to use an optimization strategy with simple gradient-based optimum-searching method and multi-section blade parameterization technique to search and generate an optimal swept rotor with curved arbitrary leading edge. Its adiabatic efficiency is a little bit greater than that of the reference un-swept rotor.

Multi-Objective Aerodynamic Optimization of Axial Turbine Blades Using a Novel Multilevel Genetic Algorithm

In this paper, a new multiploid genetic optimization method handling surrogate models of the CFD solutions is presented and applied for a multi-objective turbine blade aerodynamic optimization problem. A fast, efficient, robust, and automated design method is developed to aerodynamically optimize 3D gas turbine blades. The design objectives are selected as maximizing the adiabatic efficiency and torque so as to reduce the weight, size, and cost of the gas turbine engine. A 3D steady Reynolds averaged Navier–Stokes solver is coupled with an automated unstructured grid generation tool. The solver is verified using two well-known test cases. The blade geometry is modeled by 36 design variables plus the number of blade variables in a row. Fine and coarse grid solutions are respected as high- and low-fidelity models, respectively. One of the test cases is selected as the baseline and is modified by the design process. It was found that the multiploid multi-objective genetic algorithm successfully accelerates the optimization and prevents the convergence with local optimums.

케이싱 그루브가 존재하는 축류압축기의 성능특성 연구

This paper presents a study on the performance of NASA Rotor 37 with the casing grooves based on three-dimensional numerical analysis. Reynolds-averaged Navier-Stokes equations are solved on a hexahedral grid with the shear stress transport model as a turbulence closure model. The governing equations are discretized by a finite volume method. The validation of the numerical results is performed through experimental data for the total pressure ratio and the adiabatic efficiency. The investigation for an axial compressor with a smooth casing and the casing grooves is carried out to compare the performance parameters, for example, surge margin and efficiency, etc. The surge margin is improved in the case of the casing grooves while remarkable improvement of the efficiency is not produced. The result shows that the casing groove is beneficial to expand the operating range of NASA Rotor 37.

Rotor Wake Variability in a Multistage Compressor

Rotorwakevariability isnot typically accountedforin computational fluid dynamics models,yet small deviations from the modeled average wake could have impacts on performance and forced vibratory response of airfoils. This paper quantifies rotor wake variability, in terms of wake depth and width, for each stage in a three-stage research compressor. Time-resolved flow angle data are acquired with a cross-film sensor at midspan for all three rotor exits for 50 circumferential positions spanning a vane passage. This research focuses on rotor wake variability driven by blade row interactions. The scope of the study includes wake variations caused by blade-to-blade differences, interactions with upstream rotor wakes, and interactions with the potential field of the downstream vane row. The lowest levels of variability are associated with rotor 1. In the downstream rotors, ensemble-averaged revolutions of data show an amplitude modulation caused by interactions with the rotor wakes from the upstream blade rows and, thus, increased levels of blade-to-blade wake variability. The main effect of the downstream vane row is to shift the mean levels of the wake without significantly influencing the wake shape. Nomenclature mc = corrected mass flow rate Nc = corrected rotational speed R = rotor Rec = Reynolds number based on chord length S = stator t = time U = wheel speed V = flow velocity in the absolute reference frame W = flow velocity in the rotating reference frame � = absolute flow angle � = relative flow angle � = adiabatic efficiency � = standard deviation

Effects of Low Reynolds Number on Loss Characteristics in Transonic Axial Compressor

A three-dimensional computation was conducted to understand effects of low Reynolds numbers on loss characteristics in a transonic axial compressor, Rotor 67. As a gas turbine becomes smaller and it operates at high altitude, the engine frequently operates under low Reynolds number conditions. This study found that large viscosity significantly affects the location and intensity of the passage shock, which moves toward the leading edge and has decreased intensity at low Reynolds number. This change greatly affects performance as well as internal flows, such as pressure distribution on the blade surface, tip leakage flow and separation. The total pressure ratio and adiabatic efficiency both decreased by about 3% with decreasing Reynolds number. At detailed analysis, the total pressure loss was subdivided into four loss categories such as profile loss, tip leakage loss, endwall loss and shock loss.

Research on Flow Characteristics of Supercritical CO2 Axial Compressor Blades by CFD Analysis

A supercritical CO2 gas turbine of 20MPa is suitable to couple with the Na-cooled fast reactor since Na - CO2 reaction is mild at the outlet temperature of 800K, the cycle thermal efficiency is relatively high and the size of CO2 gas turbine is very compact. In this gas turbine cycle, a compressor operates near the critical point. The property of CO2 and then the behavior of compressible flow near the critical point changes very sharply. So far, such a behavior is not examined sufficiently. Then, it is important to clarify compressible flow near the critical point. In this paper, an aerodynamic design of the axial supercritical CO2 compressor for this system has been carried out based on the existing aerodynamic design method of Cohen1). The cycle design point was selected to achieve the maximum cycle thermal efficiency of 43.8%. For this point, the compressor design conditions were determined. They are a mass flow rate of 2035kg/s, an inlet temperature of 308K, an inlet static pressure of 8.26MPa, an outlet static pressure of 20.6MPa and a rotational speed of 3600rpm. The mean radius was constant through axial direction. The design point was determined so as to keep the diffusion factor and blade stress within the allowable limits. Number of stages and an expected adiabatic efficiency was 14 and 87%, respectively. CFD analyses by FLUENT have been done for this compressor blade. The blade model consists of one set of a guide vane, a rotor blade and a stator blade. The analyses were conducted under the assumption both of the real gas properties and also of the modified ideal gas properties. Using the real gas properties, analysis was conducted for the 14th blade, whose condition is remote from the critical point and the possibility of divergence is very small. Then, the analyses were conducted for the blade whose conditions are nearer to the critical point. Gradually, divergence of calculation was encountered. Convergence was relatively easy for the modified ideal gas properties. Main output of calculation is a value of the mass flow rate, which was larger than the design value. However the discrepancy of mass flow rates between CFD and design reduced if the 3-dimensional effects are taken into consideration. Absolute velocity distributions, relative velocity distributions and static pressure distributions surrounding rotor blade and stator blade were obtained. The characteristics of these distributions were consistent with those of the fundamental theory and these analyses were justified.

Orbiting compressor for residential air-conditioners

A new type of compressor, called an orbiting compressor, is introduced in this paper. The orbiting compressor is characterized by an orbiting piston, and the piston or orbiter consists of a circular base plate and a ring type vane protruding vertically from the base plate. The orbiter is made to orbit in an annular space formed between two concentric circular walls via an Oldham-ring mechanism, producing two sealed gas pockets on both sides of the vane wrap with a 180° phase difference. This operating mechanism leads to alternating compression and discharge processes, which results in low torque variation. The orbiting compressor has been designed for an R410A residential air conditioner with a cooling capacity of 10.0 kW. The performance of the orbiting compressor model has been analytically investigated, where the volumetric, adiabatic and mechanical efficiencies were calculated to be 94.8%, 90.4% and 93.4%, respectively for the ARI condition. The EER was estimated to be about 10.86 with a motor efficiency of 89%.

Thermodynamics of autothermal wood gasification

AbstractThis work extensively studies the thermodynamics of air blown autothermal wood gasification at adiabatic conditions. To this end, the software package HSC Chemistry® was used to determine the composition of the synthesis gas at thermodynamic equilibrium. This software operates on the basis of Gibb's energy minimization. In the model, dry and ash‐free wood has been represented by CH1.44O0.66. Dry air has been modeled as a mixture of oxygen, nitrogen and argon. As the calculations were carried out with respect to adiabatic conditions, it was necessary to determine the adiabatic flame temperature via heat and mass balances. This approach of adopting adiabatic conditions, though generally not taken into consideration in thermodynamic studies, is seen as beneficial, providing additional information with regard to the gasifier operating point. A sensitivity analysis was conducted. The influence of parameters like equivalence ratio, water content of wood fuel and air preheating on adiabatic flame temperature and cold gas efficiency is discussed. For air at ambient temperature, the highest cold gas efficiency is achieved with an equivalence ratio of about 0.28. This was dependent to some small degree on the water content of the fuel wood. With increased air preheating, the maximum cold gas efficiency is increased and shifted to lower equivalence ratios. For wet wood, it transpired to be more efficient to use the sensible heat from the synthesis gas for drying of the fuel rather than preheating of the air. Finally, calculated values are compared to measurements from a circulating fluidised bed gasifier. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Surrogate Based Optimization Techniques for Aerodynamic Design of Turbomachinery

Recent development of high speed computers and use of optimization techniques have given a big momentum of turbomachinery design replacing expensive experimental cost as well as trial and error approaches. The surrogate based optimization techniques being used for aerodynamic turbomachinery designs coupled with Reynolds-averaged Navier-Stokes equations analysis involve single- and multi-objective optimization methods. The objectives commonly tried to improve were adiabatic efficiency, pressure ratio, weight etc. Presently coupling the fluid flow and structural analysis is being tried to find better design in terms of weight, flutter and vibration, and turbine life. The present article reviews the surrogate based optimization techniques used recently in turbomachinery shape optimizations.

On the Coupling of Designer Experience and Modularity in the Aerothermal Design of Turbomachinery

The turbomachinery aerodynamic design process is characterized both by its complexity and the reliance on designer experience for success. Complexity has led to the design being decomposed into modules; the specification of their interfaces is a key outcome of preliminary design and locks-in much of the final performance of the machine. Yet preliminary design is often heavily influenced by previous experience. While modularity makes the design tractable, it complicates the appropriate specification of the module interfaces to maximize whole-system performance: coupling of modularity and designer experience may reduce performance. This paper sets out to examine how such a deficit might occur and to quantify its cost in terms of efficiency. Two disincentives for challenging decomposition decisions are discussed. The first is where tried-and-tested engineering “rules of thumb” accord between modules: the rational engineer will find alluring a situation where each module can be specified in a way that maximizes its efficiency in isolation. The second is where there is discontinuity in modeling fidelity, and hence difficulty in accurately assessing performance exchange rates between modules. In order to both quantify and reduce the potential cost of this coupling, we have recast the design problem in such a way that what were previously module interface constraints become key system design variables. An example application of our method to the design of a generic turbofan core compression system is introduced. It is shown that nearly one percentage point of the equivalent compressor adiabatic efficiency can be saved.

Introduction of a new definition for effectiveness of desiccant wheels

In common air conditioning methods, both sensible and latent loads are handled by cooling systems. Utilizing desiccant, individual cooling and dehumidification processes are possible. In this paper, desiccant wheel operation has been investigated by experimental study. Experimental conditions include different climates (hot dry and hot humid) at different operating parameters (regeneration temperature and wheel speed). Due to the temperature and humidity measurements of inlet and outlet streams, the desiccant wheel efficiency in each definition was calculated. All experiments show that enthalpy of the outlet process air is notably higher than that of the inlet air. This event leads to a novel efficiency definition which presents the deviation of the outlet process air enthalpy from the inlet air enthalpy. By increase in the dehumidification efficiency, the adiabatic efficiency decreases, whereas it increases by the regeneration efficiency. Hence in some situations the adiabatic efficiency will have an optimum value. According to the adiabatic efficiency concept, it seems to be related to the coefficient of performance of the desiccant cooling systems.

Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor

In turbocharger applications, bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly-loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a preproduction, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without the bleed flow, the prestall behavior is dominated by short-wavelength disturbances, or so called “spikes,” in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at the impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long-wavelength modal prestall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to the bleed flow and yielding a one point increase in adiabatic compressor efficiency.