Multifield coupling axial flow turbine performance prediction model and multi-objective optimization design method

Antenna plays an important role in modern communication. Accurate calculation of antenna structure to obtain reasonable electromagnetic characteristic parameters is an important part of antenna design. With the increasing complexity of the antenna structure, a large number of numerical calculations are required in the design process to determine the optimal structure size. Therefore, it’s necessary to study the fast optimization algorithm of antenna multi-objective (antenna bandwidth, gain, polarization characteristics, etc) optimization design method. In this paper, a new adaptive BF neural network is proposed to optimize the resonant frequency and size structure of dual frequency circular polarization microstrip antenna, so as to improve the efficiency of antenna design.

Chapter 7 - Turbomachinery

Modern aerodynamic optimization design methods for the industrial axial compressor cascade mainly aim at improving both design point and off-design point performance. In this study, a multi-point and multi-objective optimization design method is established for the cascade, particularly aiming at widening the operating range while maintaining good performance at the acceptable expense of computational load. The design objectives are to maximize the static pressure ratio and minimize the total pressure loss coefficient at the design point, and to maximize the operating range for the positive and negative incidences. To alleviate the computational load, a design of experiment (DOE)-based GA–BP-ANN model is constructed to rapidly approximate the cascade aerodynamic performance in the optimization process. The artificial neural network (ANN) is trained by the genetic algorithm (GA) technique and back propagation (BP) algorithm, where the training cascades are sampled by the DOE method and analysed by the computational fluid dynamics method. The multi-objective genetic algorithm is used to search for a series of Pareto-optimum solutions, from which an optimal cascade is found out whose objectives are all better than (ABT) those of the original design. The ABT cascade is characterized by the lower camber and higher turning angle, leading to better aerodynamic performance in a widened operating range. Compared with the original design, the ABT cascade decreases the total pressure loss coefficient by 1.54 per cent, 23.4 per cent, and 7.87 per cent at the incidences of 5°, −9°, and 13°, respectively. The established optimization design method can be extended to the three-dimensional aerodynamic design of axial compressor blade.

Determination Of Major Losses And Isentropic Efficiency In Axial Flow Turbines

Modelling and parametric analysis of small-scale axial and radial-outflow turbines for Organic Rankine Cycle applications

Laboratory experiments were performed to study the effect of an axial-flow hydrokinetic turbine model on an erodible channel under both clear water and live-bed conditions. Clear water experiments were performed at two scales with a local bed shear stress just below the critical state. Live-bed experiments, performed at small scale, examined the interactions between relatively large-scale bedforms and the flow induced by an axial flow turbine. Spatiotemporal topographic measurements were obtained by sonar and by a state-of-the-art high-resolution scanning system integrated into an automated data acquisition carriage designed and fabricated at the St. Anthony Falls Laboratory at the Univ. of Minnesota. Results indicate that the presence of the turbine rotor increases the local shear stress resulting in accelerated and expanded scour development when compared with typical bridge pier scour mechanisms. The inferred key difference is the alteration of the flow patterns in the rotor wake leading to an accelerated flow region below the bottom tip. The footprint of the rotor is observed in the extension and scaling of the bed surface area impacted by the turbine and consistent with the near-wake region. Temporally averaged bed topography data from live-bed experiments indicate amplified scour depths in the turbine near-wake region as compared with the clear water results despite spatial patterns remaining qualitatively similar.

Transient velocity and mixing losses in axial flow turbines with partial admission

Effect of chamber roughness and local smoothing on performance of a CAES axial turbine

Multi-objective optimal design of modification for helical gear

The operational stability of axial flow turbines (AFT) directly affects its safety and performance. Hence, dynamic analysis of its internal flow characteristics is essential, since its unsteady pressure characteristics are complicated. A reliable measurement approach becomes essential in order to analyze and understand the pressure fluctuation within the turbine. Dynamic pressure pulsation measurements were conducted by installing pressure sensors on the flow domain of the AFT under different operating conditions. Based on computational and experimental measurements, different unsteadiness in the flow structures resulted in various excitation signals. The excited frequencies of the stationary parts occurred at 72.50Hz3×fn, 145.00Hz6×fn,and217.50Hz9×fn, while for the impeller, excited frequencies of 217.50 Hz (9 × fn), 435.00 Hz (18 × fn), and 652.50 Hz (27 × fn) were recorded. The rotor–stator interaction with fluid flow from the guide vane to the impeller is culpable for strong pressure pulsations. The experimental measurement shows a comprehensive agreement with numerical results. This paper focused on the analysis of pressure fluctuation in AFT combining experimental and computational methods. Moreover, an exhaustive understanding of flow characteristics of the AFT is necessary for its optimization and operational reliability.

A numerical study has been performed to investigate the effect of tip geometry on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. Baseline flat tip geometry and squealer type geometries namely double squealer or cavity and suction side squealer were considered. The performances of the squealer geometries, in terms of the leakage mass flow and heat transfer to the tip, were compared with the flat tip at two different tip clearance gaps. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modelled using three different models namely standard k-ε, low Re k-ω and SST k-ω, in order to assess the capability of the models in correctly predicting the blade heat transfer. The heat transfer and static pressure distributions obtained using the SST k-ω model was found to be in close agreement with the experimental data. It was observed that compared to the other two geometries considered, the cavity tip is advantageous both from the aerodynamic and from the heat transfer perspectives by providing a decrease in the amount of leakage, and hence losses, and average heat transfer to the tip. In general, for a given geometry, the leakage mass flow and the heat transfer to the tip increased with increase in tip clearance gap. Part II of this paper examines the effect of relative casing motion on the flow and heat transfer characteristics of tip leakage flow. In Part III of this paper the effect of coolant injection on the flow and heat transfer characteristics of tip leakage flow is presented.

Radial-outflow turbo-expanders have emerged in the recent years to suit some special applications where complex multi-phase and multi-component flows (like liquid-rich gases and solid particle-laden gases) need to be expanded. This paper presents a systematic study on the design and flow behavior of a single stage radial-outflow turbo-expander, which is to be used in organic Rankine power system to covert the low-temperature heat into shaft power. A mean-line code coupled with the optimization algorithm is developed and used to carry out the one-dimensional preliminary design, where 7 non-dimensional parameters are used as design variables (nozzle velocity coefficient, rotor velocity coefficient, reaction, rotor inlet and outlet flow angles, velocity ratio, and rotor diameter ratio). In comparison with the original design, significant design performance gains are achieved with the matched combination of design parameters. Geometric shape design is further performed for the expander. In consideration of the flow features in nozzle and rotor blade passages being nearly two-dimensional, blade shape design of both rows is conducted on the basis of the airfoils used for conventional axial flow turbines, where a conformal mapping method is used to convert the axial profile into the polar coordinate frame and it is then represented by 11 parameters of mean cylindrical diameter, radial and tangential chord, leading and trailing edge radius, blade inlet and outlet angles, blade inlet wedge angle, number of blades, unguided turning, and throat size. Flow and overall performance are simulated and predicted for the designed expander, where the output shaft power and overall isentropic efficiency is respectively predicted as 87.86 kW and 81.60% at design condition.

Numerical investigation on flow characteristics and aerodynamic performance of shroud seal in a supercritical CO2 axial-flow turbine

Hydropower unit is the compensation power generation of the energy regulating unit in wind–solar–water multi-energy complementary systems that often require the turbine to operate in a partial working condition area, thereby resulting in problems of low hydraulic efficiency and severe vibration during operation. A multi-objective and multi-condition optimization design method for Francis turbine runner based on the super-transfer approximation approach was proposed in this study. The proposed method aims to improve the hydraulic performance of the turbine, enhance and suppress the vibration of the turbine, and expand the operation range of the turbine on the basis of the actual situation given that Francis turbine frequently operates in low- and ultralow-load areas under the condition of multi-energy complementarity and continuous adjustment of operating conditions. Different operating conditions from low load to full load were selected as performance evaluation conditions. The super-transfer approximation method was used to select the weight co-efficient of water turbine operating conditions, and a multi-objective optimization function with the efficiency and cavitation performance of the water turbine as optimization objectives was constructed to ensure that the optimized water turbine can achieve the optimal performance in the full working condition range. Results showed that the pressure distribution on the blade surface of the optimized runner was uniform and the working ability was enhanced under the condition of ensuring the performance stability of optimal and rated conditions when the original runner was optimized. The hydraulic efficiency of the turbine under the low-load conditions OP1 and OP2 increased by 4.61 and 3.17%, respectively. Hence, the optimized runner is suitable for hydraulic turbines under multi-energy complementary conditions. The results of this study can provide a reference for the optimal design and operation of the turbine runner.

Multi-objective robust optimization of a solar power tower plant under uncertainty