Zhilong He

Design of the Curved Flank for the Star-Wheel Tooth in Single Screw Compressors

The wear of star-wheel teeth is an important problem in single screw compressors. In order to prolong the service life of star wheels, a new curved flank of the tooth is proposed. Section profile of the tooth flank is a curve, which could be elliptical, hyperbolic, involute, or new defined. The screw groove flank is the envelope surface corresponding to the surface of the tooth flank. During the tooth meshing with the groove, the contact line moves in the tooth flank area.

Development of an Optimization Design Method for Turbomachinery by Incorporating the Cooperative Coevolution Genetic Algorithm and Adaptive Approximate Model

An optimization design method is developed, which is motivated by the optimal design of a cryogenic liquid turbine (including an asymmetric volute, variable stager vane nozzles, shroud impeller and diffuser) for replacement of the Joule-Thompson throttling valve in the internal compression air-separation unit. The method involves mainly three elements: geometric parameterization, prediction of objective function, and mathematical optimization algorithm. Traditional parameterization approach is used for the geometry representation, while some novel work in the latter two aspects (i.e. objective function evaluation and optimization algorithm) is done to reduce the computing time and improve the optimization solution. A modified Cooperative Coevolution Genetic Algorithms (CCGA) is developed by incorporating a modified variable classification algorithm and some new self-adapted GA operators, which help to enhance the global search ability with an excessive number of optimization variables. Design of Experiment (DOE) is carried out to initialize the kriging approximation model, which is used to approximate the time-costly objective function. Then the CCGA is started, and once a potential superior individual is found, a decision will be made by the in-house code on whether or not it needs a updating. If required, the true objective function prediction based on the real model will be conducted and the obtained value of objective function will be used to update the kriging model. In such a way, the CCGA can complete its optimal searching with a limited number of real evaluations for objective function. All the above features are integrated into the optimization framework and encoded for the optimal turbine design. In addition, CFD software ANSYS CFX is used for the real objective function evaluations, and a well-organized batch code is developed by the authors for calling the CFD simulation which helps to promote this automation of the optimization process. For validation, the optimization method is used to solve some classical mathematical optimization problems and its effectiveness is demonstrated. The method is then used in the optimal design of the cryogenic liquid turbine stage, it is demonstrated that the optimal design method can help to reduce significantly the searching time for the optimal design and improve the design solution to the liquid turbine.© 2011 ASME

Prediction of Axial Thrust Load Acting on a Cryogenic Liquid Turbine Impeller

A single stage cryogenic liquid turbine is developed for replacing the Joule-Thompson valve and recovering energy from the liquefied air during throttling process in the large-scale internal compression air-separation unit, and evaluation of the impeller axial thrust at different conditions is essential for a reliable bearing design and stable operation. To predict the axial thrust load, a numerical model is established to simulate the turbine flow in a turbine stage environment, which includes the main flow domain (an asymmetrical volute, variable geometry nozzle, impeller, and diffuser), impeller front and back side gaps, and shaft seal leakage. Numerical simulation of flow is conducted by using the ANSYS-CFX. Flow characteristics in both main flow domain and impeller side gaps of the turbine stage are captured and analyzed. The axial thrust is then calculated based on the obtained pressure data in the impeller and its front and side gaps by using a direct integration approach. Flow behaviour in both main flow domain and impeller side gaps has been well exhibited by the numerical results. At the impeller back side gap inlet, the back flow is encountered even for design condition and it returns the impeller main flow stream; the impeller side gap flow has much influence on the axial thrust. To investigate influence of turbine operation condition on axial thrust, flow simulation is conducted at different mass flow rates and inlet pressure for the turbine stage, based on which the axial thrust is calculated. It is demonstrated from the obtained numerical results that the axial thrust increases as the inlet pressure increases and decreases as turbine flow rate increases. Geometry parametric study is conducted for the shaft seal clearances, which has demonstrated that the axial thrust is influenced largely by the clearance size and it decreases as the clearance grows. For the purpose of comparison, the empirical method is also used to predict the axial thrust load. The obtained results are compared to the numerical ones and evident deviation of the empirical from the numerical exists and the reason is that axial force components caused by the impeller main flow stream and its side gap flow are approximated very roughly in the empirical method.© 2011 ASME

Flow Field Simulation and Noise Control of a Twin-Screw Engine-Driven Supercharger

With the advantages of good low-speed torque capability and excellent instant response performance, twin-screw superchargers have great potential in the automobile market, but the noise of these superchargers is the main factor that discourages their use. Therefore, it is important to study their noise mechanism and methods of reducing it. This study included a transient numerical simulation of a twin-screw supercharger flow field with computational fluid dynamics software and an analysis of the pressure field of the running rotor. The results showed that overcompression was significant in the compression end stage of the supercharger, resulting in a surge in airflow to a supersonic speed and the production of shock waves that resulted in loud noise. On the basis of these findings, optimization of the supercharger is proposed, including expansion of the supercharger exhaust orifice and creation of a slot along the direction of the rotor spiral normal line at the exhaust port, so as to reduce the compression end pressure, improve the exhaust flow channel, and weaken the source of the noise. Experimental results showed that the noise level value of the improved twin-screw supercharger was significantly lower at the same speed than the original model, with an average decrease of about 5 dB (A).

Study of aerodynamic noise in hermetic refrigerator compressor

This paper is to study the aerodynamic noise in hermetic refrigerator compressor. First, a compressor model is built and its working process is numerically simulated to obtain data of velocity and pressure in suction. Next, use the above data to calculate aerodynamic noise of two compressors, one with and the other without a suction muffler. Then improve the suction muffler and calculate it aerodynamic noise to show that it has gained better performance. Finally experimental results obtained from noise experiments verify the above conclusion.