Modelling, simulation and optimisation of asymmetric rotor profiles in twin-screw superchargers

There is a growing recognition worldwide of the need for more powerful, smaller petrol engines, capable of delivering the higher picking power of larger engines, yet still being economical and environmentally friendly when used for day-to-day driving. An engineering solution for more efficient engines has been considered by research so far. It has been identified that superchargers can potentially improve the performance of automotive engines; therefore research has focused on developing superchargers and supercharger components with higher efficiency. Of particular interest to the research presented in this thesis has been the twin-screw supercharging compressor with design adapted for automotive use (the twin-screw supercharger). The performance of this supercharger type depends on the volume and total losses of the air flow through the supercharger rotors more than on any oth er aspects of its behaviour. To accurately predict the efficiency of the twin-screw supercharger for matching a particular engine system, accurate supercharger design is required. The main objective of this research was the investigation of the existing limitations of twin-screw superchargers, in particular leakage and reduced efficiency, leading to the development of optimal asymmetric rotor profiles. This research has been completed in four stages defining an innovative rotor design method. The parametric three-dimensional geometric model of twin-screw supercharger rotors of any aspect ratio was developed. For model validation through visualisation, CAD rotor models with scalable data were generated in commercial CAD software and calibrated experimentally by Laser Doppler Velocimetry (LDV) tests. Calibrated rotor profile data can be transferred into CAD-CFD interface for flow simulation and performance optimisation. Through the application of this new rotor design method, new opportunities are created for the twin-screw supercharger design practice, making it a part of the engineering solution for more efficient engines

Numerical and Experimental Study of Screw Machines with Large Helix Angle

An effective and efficient CFD simulation is of high importance to accelerate the design activities of twin screw machines. However, mesh generation for screw machines with large helix angles can produce highly skewed numerical cells which can make simulation unreliable. From the established literature, the two main approachesto generate structured deforming mesh for CFD analysis of twin screw machines are algebraic and differential. The purpose of this thesis is to explore grid generation techniques suitable for 3D numerical modelling of rotatory positive displacement machines with large helix angles. Both cut-cell cartesian and body-fitted grid generation methods are investigated for analysis of machines with different profiles and helix angles. The conservation and simulation accuracy of cut-cell cartesian method was first evaluated using a simple piston cylinder example and a hook and claw rotor profile used in vacuum pump which is difficult to set by a body fitted mesh. It was shown that even with coarse initial mesh, such profiles could have been analysed using a cut-cell cartesian mesh, but it required special model to account for leakage flows. Secondly, screw machines with low helix angle are used to examine the capability of both grid generation methods. ANSYS CFX was used for analysis of body fitted mesh produced by SCORG grid generator, while ANSYS Forte was used for evaluation of cut-cell cartesian method. Thirdly, oil-injected twin screw compressor with intermediate helix angle was explored using body-fitted method. In addition, a case study of a twin-screw vacuum pump with higher helix angle of 62 degree was studied using SCORG and FLUENT to further explore the body-fitted method. Lastly, a twin-screw vacuum pump with variable pitch and cusp points was analysed using cut-cell cartesian method. These five case studies demonstrated advantages and disadvantages of body-fitted and cut-cell cartesian methods for low, intermediate, and large helix angles. This thesis then proposes development of an alternative method called a normal grid generation method which is expected to improve mesh quality of a body fitted mesh for screw machine with large helix angles and in turn could improve accuracy of flow calculation

Summaries of FY 1997 Research in the Chemical Sciences

The objective of this program is to expand, through support of basic research, knowledge of various areas of chemistry, physics and chemical engineering with a goal of contributing to new or improved processes for developing and using domestic energy resources in an efficient and environmentally sound manner. Each team of the Division of Chemical Sciences, Fundamental Interactions and Molecular Processes, is divided into programs that cover the various disciplines. Disciplinary areas where research is supported include atomic, molecular, and optical physics; physical, inorganic, and organic chemistry; chemical energy, chemical physics; photochemistry; radiation chemistry; analytical chemistry; separations science; heavy element chemistry; chemical engineering sciences; and advanced battery research. However, traditional disciplinary boundaries should not be considered barriers, and multi-disciplinary efforts are encouraged. In addition, the program supports several major scientific user facilities. The following summaries describe the programs

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction