Turbine Preliminary Design Research Articles

Inviscid analysis of horizontal axis wind turbines using distributed vorticity elements

The primary tool currently used for a wind turbine preliminary design is the blade element momentum method, which lacks a detailed wake model and relies on an assumption of non-interacting streamtubes. These simplifications limit the designer's ability to tailor the blade shape to minimize the induced power loss of the rotor. Improved prediction of the induced velocity distribution on the blades can be achieved through the use of vortex-based models at a computational cost low enough for use in design processes requiring many iterations. This paper presents the implementation of a potential flow, lifting-surface methodology using elements of distributed vorticity. The use of such elements provides several advantages including higher resolution than filament-based methods, simulation of non-planar blade planforms, and avoids the need for empirical corrections. Because the wake has a strong influence on the flow at the rotor, the accurate prediction of its geometry is highly important for wind turbine analysis. To this end, a force-free relaxed-wake model is presented as well as less numerically intensive fixed-wake and hybrid-wake models. Comparison is made to the blade element momentum method and Goldstein's theoretical solution for the ideal lightly loaded rotor.

Modelling of Combustor Non-Uniformities Evolution Through a High-Pressure Turbine Stage

Abstract In modern gas turbines, the reduction of pollutant emissions can be achieved by employing lean-burn combustors. At the combustion chamber outlet, the flow is non-uniform and characterized by a residual swirl superimposed to steady (hot streak) and unsteady (entropy waves) temperature disturbances. During the transport from the combustor outlet to the turbine inlet, these disturbances are weakly dissipated and persist at the turbine inlet. Therefore, the interaction between the combustor non-uniformities and the turbine has to be deeply studied. To study combustor-turbine interaction experimentally, a common practice is to install combustor simulators on non-reactive turbine test facilities. For this purpose, a combustor simulator was designed and installed at Politecnico di Milano turbine test facility. This device can generate a combined steady/unsteady temperature disturbance and swirl profile at the turbine inlet. Using this layout, several experimental campaigns have been carried out changing the type of injected disturbance, the injection position and the turbine operating condition. In this paper, the data collected from these experiments have been used to develop simplified models to predict the transport and dissipation of combustor perturbations through a turbine first stage. In the open literature, few attempts are discussed regarding the modelling of combustor-turbine interaction that - in authors' opinion - represents an important tool for preliminary turbine design.

Design of the Organic Rankine Cycle for High-Efficiency Diesel Engines in Marine Applications

Over the past few years, fuel prices have increased dramatically, and emissions regulations have become stricter in maritime applications. In order to take these factors into consideration, improvements in fuel consumption have become a mandatory factor and a main task of research and development departments in this area. Internal combustion engines (ICEs) can exploit only about 15–40% of chemical energy to produce work effectively, while most of the fuel energy is wasted through exhaust gases and coolant. Although there is a significant amount of wasted energy in thermal processes, the quality of that energy is low owing to its low temperature and provides limited potential for power generation consequently. Waste heat recovery (WHR) systems take advantage of the available waste heat for producing power by utilizing heat energy lost to the surroundings at no additional fuel costs. Among all available waste heat sources in the engine, exhaust gas is the most potent candidate for WHR due to its high level of exergy. Regarding WHR technologies, the well-known Rankine cycles are considered the most promising candidate for improving ICE thermal efficiency. This study is carried out for a six-cylinder marine diesel engine model operating with a WHR organic Rankine cycle (ORC) model that utilizes engine exhaust energy as input. Using expander inlet conditions in the ORC model, preliminary turbine design characteristics are calculated. For this mean-line model, a MATLAB code has been developed. In off-design expander analysis, performance maps are created for different speed and pressure ratios. Results are produced by integrating the polynomial correlations between all of these parameters into the ORC model. ORC efficiency varies in design and off-design conditions which are due to changes in expander input conditions and, consequently, net power output. In this study, ORC efficiency varies from a minimum of 6% to a maximum of 12.7%. ORC efficiency performance is also affected by certain variables such as the coolant flow rate, heat exchanger’s performance etc. It is calculated that with the increase of coolant flow rate, ORC efficiency increases due to the higher turbine work output that is made possible, and the condensing pressure decreases. It is calculated that ORC can improve engine Brake Specific Fuel Consumption (BSFC) from a minimum of 2.9% to a maximum of 5.1%, corresponding to different engine operating points. Thus, decreasing overall fuel consumption shows a positive effect on engine performance. It can also increase engine power output by up to 5.42% if so required for applications where this may be deemed necessary and where an appropriate mechanical connection is made between the engine shaft and the expander shaft. The ORC analysis uses a bespoke expander design methodology and couples it to an ORC design architecture method to provide an important methodology for high-efficiency marine diesel engine systems that can extend well beyond the marine sector and into the broader ORC WHR field and are applicable to many industries (as detailed in the Introduction section of this paper).

Optimized Design of a Novel Hydraulic Propeller Turbine for Low Heads

In the present paper, an optimized design procedure capable of providing the geometry of a high efficiency compact hydraulic propeller turbine for low head is proposed and developed. The turbine preliminary design is based on fundamental turbomachinery mean-line equations and on the employment of statistical correlations, which relate the main geometrical parameters to the fundamental design parameters. The first obtained geometry represents the starting point of an automated aerodynamic single point optimization procedure based on a genetic algorithm generating and updating a wide database of turbine geometries. The approach employs a three-dimensional (3D) Reynolds averaged Navier–Stokes (RANS) solver for the construction of the corresponding database of performance. A meta-model, such as an artificial neural network (ANN), is used to speed up the design optimization process. The procedure has been applied on the practical case of a novel simplified hydraulic propeller turbine prototype for very low heads. The adopted design optimization procedure is able to modify the turbine blade and vane geometries in order to achieve automatically the targeted net head and the maximum for the total to total internal efficiency once diameter, mass flow rate, and rotational speed are assigned.

The Development and Applications of a Loading Distribution Based Tip Leakage Loss Model for Unshrouded Gas Turbines

Abstract The prediction of tip leakage flow aerothermal loss plays a crucial role in turbine preliminary design, which strongly affects the turbine performance. A new tip leakage loss model for unshrouded turbine is developed in this paper, considering the compressible flow aerothermal process inside the clearance. By coupling with a parameterized loading distribution model proposed in this work, in which the blade loading can be described by four independent parameters, Zweifel coefficient (Zw), diffusion factor (DF), peak velocity location (PVL), and leading edge acceleration (LEA), the loss model can evaluate the tip leakage loss in aerodynamic design process conveniently and accurately. The proposed models are validated by numerical simulations and the results show that, compared with the other acknowledged loss models, the loss model can reduce the deviations by more than 50%. Based on the models, the effects of blade loading design parameters on tip leakage losses are discussed via analysis of variance (ANOVA). The results show that Zw has the most significant influence. As Zw decreases from 1.0 to 0.7, tip leakage losses can be reduced by about 16%. Under lower Zw conditions, the joint effect of PVL and LEA is remarkable. However, under higher Zw conditions, the joint effect of the DF and PVL is more important.

New Supersonic Loss Model for the Preliminary Design of Transonic Turbine Blades and the Influence of Pitch

Abstract In order to produce a more efficient design of a compact turbine driving a cryogenic engine turbo-pump for a satellite delivering rocket, a new supersonic loss model is proposed. The new model was constructed based on high-quality published data, composed of Schlieren photographs and experimental measurements, that combined provided a unique insight into the mechanisms driving supersonic losses. Using this as a cornerstone, model equations were formulated that predict the critical Mach number and shock loss and shock-induced mixing loss as functions of geometrical (i.e., blade outlet and uncovered turning angle and trailing edge thickness) and operational parameters (i.e., exit Mach number). A series of highly resolved CFD numerical simulations were conducted on an in-house designed state-of-the-art transonic turbine rotor row (around unity aspect ratio (AR)) to better understand changes in the shock system for varying parameters. The main outcome showed that pitch to chord ratio has a powerful impact on the shock system, and thus on the manner by which shock loss and shock-induced mixing loss is distributed to compose the overall supersonic losses. The numerical loss estimates for two pitch to chord ratios—t⁄c = 0.70 and t⁄c = 0.98—were compared with absolute loss data of a previously published similar blade with satisfactory agreement. Calibrated equations are provided to allow hands-on integration into existing overall turbine loss models, where supersonic losses play a key role, for further enhancement of preliminary turbine design.

Investigation of a Radial Turbines Compatibility for Small Rocket Engine

In the radial turbine preliminary design for an expander rocket engine, a comparison was made with axial turbine used in Pratt & Whitney RL10 engine. One of the primary requirements of a liquid propellant rocket engine is the generation of a high thrust, which depends on both the mass flow rate of the propellant and the pressure in the thrust chamber. In expander-cycle engines, which are the subject of the present study, the liquid propellant is first compressed using centrifugal turbo-pumps, then it is used to cool the combustion chamber and the nozzle and, once vaporized, it flows through the turbines used to drive the turbo-pumps. The aim was to demonstrate the greater efficiency of the radial turbine with a reduction of the pressure ratio with respect to the axial turbine.

Thermodynamic and economic investigations of transcritical CO2-cycle systems with integrated radial-inflow turbine performance predictions

Transcritical CO2 (TCO2) cycle systems have emerged as a promising power-generation technology in certain applications. In conventional TCO2-cycle system analyses reported in the literature, the turbine efficiency, which strongly determines the overall system performance, is generally assumed to be constant. This may lead to suboptimal designs and optimization results. In order to improve the accuracy and reliability of such system analyses and offer insight into how knowledge of these systems from earlier analyses can be interpreted, this paper presents a comprehensive model that couples TCO2-cycle calculations with preliminary turbine design based on the mean-line method. Turbine design parameters are optimized simultaneously to achieve the highest turbine efficiency, which replaces the constant turbine efficiency used in cycle calculations. A case study of heat recovery from an internal combustion engine (ICE) using a TCO2-cycle system with a radial-inflow turbine is then considered, with results revealing that the turbine efficiency is influenced by the system's operating conditions, which in turn has a significant effect on system performance in both thermodynamic and economic terms. A more generalized heat source is then considered to explore more broadly the role of the turbine in determining TCO2-cycle power-system performance. The more detailed turbine-design modelling approach allows errors of the order of up to 10–20% in various predictions to be avoided for steady-state calculations, and potentially of an even greater magnitude at off-design operation. The model allows quick preliminary designs of radial-inflow turbines and reasonable turbine performance predictions under various operating conditions, and can be a useful tool for more accurate and reliable thermo-economic studies of TCO2-cycle systems.

Toward the Integrated Design of Organic Rankine Cycle Power Plants: A Method for the Simultaneous Optimization of Working Fluid, Thermodynamic Cycle, and Turbine

Abstract The conventional design of organic Rankine cycle (ORC) power systems starts with the selection of the working fluid and the subsequent optimization of the corresponding thermodynamic cycle. More recently, systematic methods have been proposed integrating the selection of the working fluid into the optimization of the thermodynamic cycle. However, in both cases, the turbine is designed subsequently. This procedure can lead to a suboptimal design, especially in the case of mini- and small-scale ORC systems, since the preselected combination of working fluid and operating conditions may lead to infeasible turbine designs. The resulting iterative design procedure may end in conservative solutions after multiple trial-and-error attempts due to the strong interdependence of the many design variables and constraints involved. In this work, we therefore present a new design and optimization method integrating working fluid selection, thermodynamic cycle design, and preliminary turbine design. To this purpose, our recent 1-stage continuous-molecular targeting (CoMT)-computer-aided molecular design (CAMD) method for the integrated design of the ORC process and working fluid is expanded by a turbine meanline design procedure. Thereby, the search space of the optimization is bounded to regions where the design of the turbine is feasible. The resulting method has been tested for the design of a small-scale high-temperature ORC unit adopting a radial-inflow turbo-expander. The results confirm the potential of the proposed method over the conventional iterative design practice for the design of small-scale ORC turbogenerators.

Experimental, numerical and theoretical investigations of Tesla turbines

We use analytical, numerical and experimental methods to characterize the laminar flow inside a Tesla turbine rotor gap. A comparison based on one particular set of operating conditions mutually validates the three approaches. The simplicity of the analytical flow model allows for a cost efficient optimization of the underlying turbine parameters. Performance charts exhibit general trends and serve as a guide for preliminary turbine design and optimization. In terms of the ratio of half the gap width to inlet radius and the ratio of outletto inlet radius, the designer of a tesla turbine has to find a compromise between optimal efficiency and optimal power output.

A Comparison of Organic and Steam Rankine Cycle Power Systems for Waste Heat Recovery on Large Ships

This paper presents a comparison of the conventional dual pressure steam Rankine cycle process and the organic Rankine cycle process for marine engine waste heat recovery. The comparison was based on a container vessel, and results are presented for a high-sulfur (3 wt %) and low-sulfur (0.5 wt %) fuel case. The processes were compared based on their off-design performance for diesel engine loads in the range between 25% and 100%. The fluids considered in the organic Rankine cycle process were MM(hexamethyldisiloxane), toluene, n-pentane, i-pentane and c-pentane. The results of the comparison indicate that the net power output of the steam Rankine cycle process is higher at high engine loads, while the performance of the organic Rankine cycle units is higher at lower loads. Preliminary turbine design considerations suggest that higher turbine efficiencies can be obtained for the ORC unit turbines compared to the steam turbines. When the efficiency of the c-pentane turbine was allowed to be 10% points larger than the steam turbine efficiency, the organic Rankine cycle unit reaches higher net power outputs than the steam Rankine cycle unit at all engine loads for the low-sulfur fuel case. The net power production from the waste heat recovery units is generally higher for the low-sulfur fuel case. The steam Rankine cycle unit produces 18% more power at design compared to the high-sulfur fuel case, while the organic Rankine cycle unit using MM produces 33% more power.

Method for the Preliminary Fluid Dynamic Design of High-Temperature Mini-Organic Rankine Cycle Turbines

Widespread adoption of renewable energy technologies will arguably benefit from the availability of economically viable distributed thermal power conversion systems. For this reason, considerable efforts have been dedicated in recent years to R&D over mini-organic Rankine cycle (ORC) power plants, thus with a power capacity approximately in the 3–50 kW range. The application of these systems for waste heat recovery from diesel engines of long-haul trucks stands out because of the possibility of achieving economy of production. Many technical challenges need to be solved, as the system must be sufficiently efficient, light, and compact. The design paradigm is therefore completely different from that of conventional stationary ORC power plants of much larger capacity. A high speed turbine is arguably the expander of choice, if high conversion efficiency is targeted, thus high maximum cycle temperature. Given the lack of knowledge on the design of these turbines, which depends on a large number of constraints, a novel optimal design method integrating the preliminary design of the thermodynamic cycle and that of the turbine has been developed. The method is applicable to radial inflow, axial and radial outflow turbines, and to superheated and supercritical cycle configurations. After a limited number of working fluids are selected, the feasible design space is explored by means of thermodynamic cycle design calculations integrated with a simplified turbine design procedure, whereby the isentropic expansion efficiency is prescribed. Starting from the resulting design space, optimal preliminary designs are obtained by combining cycle calculations with a 1D mean-line code, subject to constraints. The application of the procedure is illustrated for a test case: the design of turbines to be tested in a new experimental setup named organic rankine cycle hybrid integrated device (ORCHID) which is being constructed at the Delft University of Technology, Delft, The Netherlands. The first turbine selected for further design and construction employs siloxane MM (hexamethyldisiloxane, C6H18OSi2), supercritical cycle, and the radial inflow configuration. The main preliminary design specifications are power output equal to 11.6 kW, turbine inlet temperature equal to 300 °C, maximum cycle pressure equal to 19.9 bar, expansion ratio equal to 72, rotational speed equal to 90 krpm, inlet diameter equal to 75 mm, minimum blade height equal to 2 mm, degree of reaction equal to 0.44, and estimated total-to-static efficiency equal to 77.3%. Results of the design calculations are affected by considerable uncertainty related to the loss correlations employed for the preliminary turbine design, as they have not been validated yet for this highly unconventional supersonic and transonic mini turbine. Future work will be dedicated to the extension of the method to encompass the preliminary design of heat exchangers and the off-design operation of the system.

Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part A: Turbine Model

Axial-flow turbines represent a well-established technology for a wide variety of power generation systems. Compactness, flexibility, reliability and high efficiency have been key factors for the extensive use of axial turbines in conventional power plants and, in the last decades, in organic Rankine cycle power systems. In this two-part paper, an overall cycle model and a model of an axial turbine were combined in order to provide a comprehensive preliminary design of the organic Rankine cycle unit, taking into account both cycle and turbine optimal designs. Part A presents the preliminary turbine design model, the details of the validation and a sensitivity analysis on the main parameters, in order to minimize the number of decision variables in the subsequent turbine design optimization. Part B analyzes the application of the combined turbine and cycle designs on a selected case study, which was performed in order to show the advantages of the adopted methodology. Part A presents a one-dimensional turbine model and the results of the validation using two experimental test cases from literature. The first case is a subsonic turbine operated with air and investigated at the University of Hannover. The second case is a small, supersonic turbine operated with an organic fluid and investigated by Verneau. In the first case, the results of the turbine model are also compared to those obtained using computational fluid dynamics simulations. The results of the validation suggest that the model can predict values of efficiency within ± 1.3%-points, which is in agreement with the reliability of classic turbine loss models such as the Craig and Cox correlations used in the present study. Values similar to computational fluid dynamics simulations at the midspan were obtained in the first case of validation. Discrepancy below 12 % was obtained in the estimation of the flow velocities and turbine geometry. The values are considered to be within a reasonable range for a preliminary design tool. The sensitivity analysis on the turbine model suggests that two of twelve decision variables of the model can be disregarded, thus further reducing the computational requirements of the optimization.

Design optimization of partial admission axial turbine for ORC service

An analysis of the application of a single stage partial admission axial turbine in organic Rankine cycle is presented. The cycle is utilized to recover the heat rejected by an internal combustion engine. The selected fluid is R245fa, whose real gas behavior is relevant under the studied conditions, as modeled by the Redlich–Kwong–Soave equation of state. A loss model for the flow through the axial blades is proposed in this work based on the boundary layer theory, the concept of diffusion factor, wind tunnel cascade tests available in literature and the conservation equations for compressible flow. The basic geometry and dimensions needed to achieve maximum turbine efficiency are determined under several subcritical and supercritical cycle conditions by means of a restrained design optimization algorithm. The single stage turbine preliminary design is shown to be greatly influenced by media compressibility and the use of convergent-divergent profiled nozzles is promising to achieve the highest possible performance potential, especially at high evaporator pressure conditions.

One Stage Power Turbine Preliminary Design and Analysis

Design and development of gas turbine components are a complex multidisciplinary process. At the beginning of the power class definition and engine configuration it is necessary to conduct a market study. The results obtained are used in gas turbine thermodynamic cycle calculations and analysis in order to define the gas turbine design point. Several possible design points are evaluated during this procedure. After this step, the gas turbine components are designed, including: compressor, combustion chamber and turbine. For industrial gas turbine purposes, it is common to use a free turbine after the gas generator, also commonly named power turbine. In this work, a power turbine was initially designed by meanline techniques, considering internal loss mechanisms, to obtain the main dimensions. The geometries of the components were generated in a 3-D environment to make possible the mesh generation, process to discretize the physical domain into a computational domain and use a 3-D Computational Fluid Dynamics tool. The results from the meanline approach and from the 3-D turbulent flow numerical simulations were compared to verify the turbine operational conditions and its predictions at design and offdesign conditions. The gas turbine under study is a project, derived from a low thrust turbojet previously developed by Instituto de Aeronáutica e Espaço. The power turbine project uses the same turbojet gas generator, already designed and currently under tests.

System and component modelling and optimisation for an efficient 10 kWe low-temperature organic Rankine cycle utilising a radial inflow expander

Small-scale (10 kWe) organic Rankine cycles for low temperature applications such as heat recovery and solar power present a significant development opportunity but limited prototypes have been developed. This paper aims to address this by describing a system modelling tool which is used to select a working fluid, optimise cycle conditions, and preliminarily size a radial inflow rotor for an experimental test rig. The program is a steady-state sizing and optimisation tool which advances on current models by combining component models and cycle analysis with multi-objective optimisation and turbomachinery design aspects. Sizing and off-design pump and expander models are based on non-dimensional characteristic plots, whilst an additional design program achieves an expander rotor design. A novel objective function couples component and system performance with complexity. Results from an optimisation study indicate that R1234ze is the optimal working fluid for the defined objective function with a predicted net power output of 7.32 kWe, correlating to a cycle efficiency of 7.26%, and evaporator and condenser areas of 1.59 m2 and 2.40 m2, respectively. However, after considering operating pressures and fluid availability, R245fa has been highlighted as the most suitable fluid for a planned experimental radial expander test rig and a preliminary turbine design is proposed.

A New Criterion to Optimize ORC Design Performance using Efficiency Correlations for Axial and Radial Turbines

Several studies on Organic Rankine Cycles (ORCs) in the literature search for the optimal cycle parameters and working fluids that maximize the net power output. Only few studies carry out a preliminary turbine design to calculate an accurate value of turbine efficiency, but this is done only after the cycle thermodynamic optimization is performed assuming a fixed and somewhat arbitrary value of turbine efficiency. Instead, a new design optimization procedure of ORCs is proposed here which embeds correlations for the design efficiency of both axial and radial turbines. The correlations are obtained from published data in the literature and use the volumetric expansion ratio (VR) and the size parameter (VH) as performance predictors. While been applied to a selected number of working fluids and single stage turbines, the procedure has a general validity being the correlations applicable to any fluid and turbine type. Results show how the turbine efficiency, and in turn the optimum cycle parameters, are influenced by the fluid properties through the turbine VH and VR values, highlighting that the procedure for working fluid selection cannot ignore the real turbine behaviour. So, the optimum design that is obtained is expected to give a behaviour much closer to reality.

Optimization of the blade trailing edge geometric parameters for a small scale ORC turbine

In general, the method proposed by Whitfield and Baines is adopted for the turbine preliminary design. In this design procedure for the turbine blade trailing edge geometry, two assumptions (ideal gas and zero discharge swirl) and two experience values (WR and γ) are used to get the three blade trailing edge geometric parameters: relative exit flow angle β6, the exit tip radius R6t and hub radius R6h for the purpose of maximizing the rotor total-to-static isentropic efficiency. The method above is established based on the experience and results of testing using air as working fluid, so it does not provide a mathematical optimal solution to instruct the optimization of geometry parameters and consider the real gas effects of the organic, working fluid which must be taken into consideration for the ORC turbine design procedure. In this paper, a new preliminary design and optimization method is established for the purpose of reducing the exit kinetic energy loss to improve the turbine efficiency ηts, and the blade trailing edge geometric parameters for a small scale ORC turbine with working fluid R123 are optimized based on this method. The mathematical optimal solution to minimize the exit kinetic energy is deduced, which can be used to design and optimize the exit shroud/hub radius and exit blade angle. And then, the influence of blade trailing edge geometric parameters on turbine efficiency ηts are analysed and the optimal working ranges of these parameters for the equations are recommended in consideration of working fluid R123. This method is used to modify an existing ORC turbine exit kinetic energy loss from 11.7% to 7%, which indicates the effectiveness of the method. However, the internal passage loss increases from 7.9% to 9.4%, so the only way to consider the influence of geometric parameters on internal passage loss is to give the empirical ranges of these parameters, such as the recommended ranges that the value of γ is at 0.3 to 0.4, and the value of τ is at 0.5 to 0.6.

Mapping Engineering Design Processes onto a Service-grid: Turbine Design Optimization

This study presents an application of a distributed service-oriented architecture (FIPER) for the preliminary design of gas turbines. The FIPER architecture is based on the concept of registration and discovery of services in real time. It uses a service catalog that registers the services started on the network. These services are then discovered in real time from the grid and used in the design process. The turbine preliminary design process involves changing the configuration of the turbine incrementally and evaluating its performance using analysis (simulation) code. During the design process a one-dimensional analysis code is wrapped into a service using a standard interface developed in FIPER and launched on the network. Several such services were distributed across a grid of workstations. These services were then used to support the turbine configuration optimization process. The study presents the results of the optimization as well as the scalability characteristics of the service-grid.

Advanced Gas Turbine Concept, Design and Evaluation Methodology. Preliminary Design of Highly Loaded Low Pressure Gas Turbine of Aircraft Engine

This article deals with the conceptual approach to optimize efficiency and power of a highly loaded gas turbine flow path design. Different problems were analyzed during low pressure turbine (LPT) preliminary design of high-bypass aircraft jet engine.