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To study the pressure pulsation characteristics of the cryogenic expander, the numerical simulation was performed on the expander hydraulic model by the numerical simulation method. Firstly, external characteristics of expander were obtained by steady numerical simulation. Simulation results were compared with test results, verifying the accuracy of simulation results. The unsteady numerical simulation was performed based on the results of steady numerical simulation.The time-domain plot at different monitoring points of the guide vane and the runner was drawn, and the frequency-domain plot at monitoring points was obtained through fast Fourier transform. The results show that the effect of dominant frequency at the monitoring point of the runner on fluid is as consistent as that of the number of the guide vanes and the effect of dominant frequency at the monitoring point of the guide vanes on fluid is as consistent as that of the number of the runner. The amplitude of the dominant frequency at the monitoring point is related to the point location. When the monitoring point is close to the vaneless area between the guide vane and the runner, the amplitude is larger. The further the distance from the vaneless area is, the smaller the amplitude is, and the smaller the influence of dynamic and static interference between the guide vane and the runner is. The research could provide reference for the design of cryogenic expander.

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objectives] In order to study the unsteady hydrodynamic performance of turbines under changing current conditions,[Method] this paper uses the Dynamic Fluid Body Interaction(DFBI) method based on an overset grid to simulate the unsteady hydrodynamic performance of turbines under different flow conditions. [Results] The results show that the DFBI method based on an overset grid can realize the monitoring of such transient parameters as speed, torque and flow field in the three stages of starting, acceleration and stabilization of the turbine during start-up. The power coefficient of the turbine has a peak value near the design flow rate of 1.2 m/s. Under dynamic conditions, the average energy efficiency of the turbine is about 0.181, which is about 33% lower than the designed flow rate of 1.2 m/s. [Conclusions] The numerical simulation method used in this paper can monitor the hydrodynamic performance of passively rotating turbines under real current conditions, and changes in the characteristic parameters of the turbine flow field and power output under passive rotation conditions, which can play an important role in guiding actual engineering design.

The high-speed centrifugal compressor used in the air supply system is the major noise source of the fuel cell vehicle. Therefore, it is important for the compressor to achieve low noise level as well as high compression ratio and efficiency. This paper presents an optimal design method for the centrifugal compressors using numerical simulation, Kriging model and genetic algorithm at the operating point. The rotational speed at the operation point is 80 000 r/min, the mass flow rate is 0.08 kg/s, and the compression ratio is 1.65. The steady RANS simulations are preliminarily used to provide the performance maps as well as the consistent initial conditions for the subsequent unsteady simulations. Performance maps are compared between numerical and experimental results at 40 000 and 50 000 r/min, which show a good agreement. Next, the unsteady simulations are performed to calculate the sound power level of the compressor. In order to analyze the influences of the blade inlet angle, blade outlet angle, trailing edge angle, tip clearance and blade thickness on the compression ratio, isentropic efficiency and sound power level, the optimal Latin square design is adopted to create the sample space. Each one of the sample points is simulated with the presented numerical method. The results show that the tip clearance and blade thickness are 2 primary factors. The compression ratio and efficiency decline when the tip clearance and blade thickness decrease, while the sound power level rises. The front incline is found to be better than the back incline. The Kriging model is built to reflect the functional relationship between the impeller design parameters and the performance parameters. Then, the multi-objective optimization is conducted with the genetic algorithm based on the Kriging model instead of the numerical model. The errors of the compression ratio, isentropic efficiency and sound power level between the Kriging model and the numerical model at optimized point are 0.11%, 0.46% and 0.01%, respectively. The blade inlet angle, blade outlet angle, trailing edge inclined angle, tip clearance and blade thickness of the baseline design are 37°, 45°, 26.7°, 0.3 mm and 1.2 mm, and the optimized design are 35.226°, 50.863°, -2.465°, 0.365 mm and 0.611 mm, respectively. Compared with the initial design, the compression ratio and isentropic efficiency of the optimal design are increased by 3.56% and 1.02%, respectively and the sound power level is decreased by 3.79 dB. The sound pressure spectrums show that the noise at blade passing frequency decreases by 16 dB. The rotational frequency and its noise at the harmonic frequency as well as broadband noise at the 0-1 800 Hz and 10 000-16 000 Hz also decrease. The compression ratio and isentropic efficiency of the centrifugal compressor are also improved at the off-design points. Internal flow fields are analyzed to find out the mechanism of the improvements. The results show that the velocity distribution is more uniform and the secondary flows in the blade flow channel significantly decrease after optimization, which means that the mixing loss at the impeller outlet decreases. This research provides a reference for optimizing the acoustic behavior as well as the performance parameters of centrifugal compressors at the early design stage. [ABSTRACT FROM AUTHOR]