Project SECRET - CFD Analysis

Project SECRET - CFD Analysis

CFD analysis on the effect of discharge port geometry of the hook and claw vacuum pumps

 

Due to the sharp discontinuities in the profile of hook and claw pumps which make it difficult to produce a good quality body fitted mesh, their CFD simulations are challenging. However, the cut-cell Cartesian meshing method is capable to handle the very complex moving geometries and is easy to setup. However it may lead to conservativeness issues. The aim of this paper is to investigate the influence of discharge port geometry of the hook and claw pump on its performance by using commercial software ANSYS Forte, which utilizes automatic mesh generation using the cut-cell Cartesian method. Firstly, five discharge ports with different geometries were designed. Secondly, the pumps with these different port configurations were set up and ran in the ANSYS Forte. Finally, the power and volume flow rate were compared. It was noticed that the geometry with the extended discharge port tip and the preliminary discharge port opening result in performance and reliability improvements. The simulation results can be used to further optimize the discharge port during the design of these machines.

Extract

 

The main focus in the design process of a claw vacuum pump is the generation of the rotors. The shape of the rotors defines the main performance characteristics of the pump which are related to the displacement and the leakage flows. The rotor design is achieved usually within a coding software like MATLAB or FORTRAN with the use of derived geometrical equations that define the curve plot of each rotor. Stosic et al. (2018) [10] provided a clear mathematical approach on rotor generation which used the envelope method to acquire the meshing points and meshing conditions of the rotors. Later on, a set of coordinates and their derivatives were obtained generating a variety of primary curves. The rest of the curves were calculated automatically using numerical series. For the optimization of the rotors, an investigation of each rotor feature must be conducted separately. Many studies have focused in the analysis of different aspects of the rotors with impressing results. For example, Yan et al. (2017) [11] noted that the use of involute-cycloid profiles leads to increased efficiency that results in larger mass flow rate while also larger mass flow pulsation. Also, Lu et al. (2015) [12] added that by combining a large flow cross section area with a small sealing line and a small blow hole area will lead in higher efficiency.

Lastly, Stosic et al. (2011) [13] highlighted that despite the level that rotor generation has reached, there is always more space for improvement in making lighter and more efficient rotors. Moving on from the rotors, other characteristics regarding the casing also affect the performance of the pump. These include: The port design, the axis distance, the axial clearance and the radial and interlobe gaps.

 

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