CFD integrated design of screw compressors

Positive displacement screw machines are used in variety of applications such as compressors, expanders, blowers, vacuum pumps, liquid and multiphase pumps. To improve their appearance, efficiency and robustness they are designed with the aid of analytical tools, based often on one-dimensional flow models solved by numerical methods that are confirmed by experiment. Continuing demand for further improvements has led to the need for improved assessment of fluid flow losses in the inlet and outlet openings and how these are affected by the shape of the ports, the deformation of machine components due to the effects of pressure and temperature gradients and their effect on performance, the behaviour of multiphase flows and many other effects. These require more advanced analytical procedures, based on three dimensional numerical flow analysis and fluid-structure interaction. The way to estimate these phenomena is to use CFD analysis and to integrate the results with three dimensional CAD systems. As computers become cheaper and faster and advances are made in numerical methods, such techniques are becoming available for everyday use by design engineers. This paper describes how CFD is merged with other design software by means of an integral management system to obtain interactive control of the entire design process of screw compressors. The methods described are of considerable scope and can be applied, not only to screw compressors but also to any other type of twin rotor rotary machines with parallel axes, such as gear pumps, multiphase pumps, vacuum pumps and roots blowers.