Serena Morselli, Giuseppe Miccoli, Karim Hamiche, Cristian Ferrari, Serena Morselli, Giuseppe Miccoli, Cristian Ferrari
(IMAMOTER C.N.R, Italy);
(Siemens Digital Industries Software, Belgium)
Predictions of the noise field emitted by an external gear pump are presented in this paper, making use of hybrid numerical integrated approaches together with some acceleration measurements on the external casing surface of the pump.
In some other previous papers published by the authors, the noise field radiated by the pump was computed by means of finite element vibro-acoustic simulations involving the structural dynamic response as excitation boundary condition of a structural FEM (Finite Element Method) model linked to an acoustic BEM (Boundary Element Method) model.
In this paper the implementation of a further multiphysics approach is illustrated. The method is based on using the external gear pump inner pressure distributions, output of a CFD (Computational Fluid Dynamics) analysis, as input of the structural model of the pump in order to compute the vibro-acoustic model.
CFD results are obtained by using a dynamic mesh approach capable of achieving an effective transient simulation of the fluid flow development inside the volume. The code uses a k-ω SST turbulence model capable of providing an accurate distribution of the relevant parameters at the boundaries of the pump. This CFD-FEM approach proves to be an efficient pump design tool by allowing an estimate of fluid power, structural and vibro-acoustics characteristics of the component starting from its CAD representation.
Gear pumps are a rotary displacement pumps consisting of two meshing gear wheels in a suitable casing whose contra-rotation drags the fluid from one side (low pressure) and discharges it on the other side at a higher pressure (Fig. 1). These components are widely used, in particular for energy transmission in hydraulic circuits and fluid power systems [1-3].
In the present work, a first approach on a CFD/FEM model was developed in order to predict the sound generated by an external gear pump during its working cycle. The pump inner pressure distribution is evaluated by a 3D CFD sub-model, afterwards, the structural displacements is calculated by a structural FEM sub-model and finally, the results are computed in the FEM vibro-acustic sub-model.
Figure 1: Simulated gear pump, exploded view
Figure 2: Complete model development
The commercial gear pump used for this application is produced by Galtech. Some geometrical simplification are implemented in the 3D CAD model in order to reduce the computational cost such as the elimination of the lateral bushes and the linked leakage.
The workflow (Fig. 2) is implemented with two commercial codes: ANSYS and Siemens Simcenter 3D.
The first part of the process, following the CAD geometry representation, concerns the extrapolation of the fluid domain from the 3D CAD model. The fluid region includes two domains: a rotating volume, made up of the gears rotation region, and a stationary domain, consisting of the pump suction and delivery volumes.
The grids used in the calculations were generated by means of ANSYS ICEM . Two unstructured mesh topologies are implemented on the model: a constant mesh and a deforming mesh, for the in-meshing fluid (Fig. 3). The moving gear contact point imposes a difficult simulation of the in-meshing fluid, moreover, the rapidly-changing domain forces the implementation of a deforming mesh [5-6]. After the extrapolation of the fluid domain, an iterative remeshing circle is executed thanks to ANSYS Fluent Dynamic Mesh algorithms .
The commercial CFD code solves the 3D Reynolds-averaged form of the Navier–Stokes equations by using a finite element-based finite-volume method. The SST k-ω two-equation model was used to solve the turbulent flow problem. Near-wall effects are modelled by means of automatic wall functions . The convergence criteria on the equations residual values are set to 10−4.
Figure 3: Mesh of the CFD fluid domain
Figure 4: Numerical displacement computed with FEM sub-model.
After the CFD simulation, the fluid-dynamic results are used to calculate the structural vibrations of the gear pump. The structural FEM mesh is generated by the automatic setting of ANSYS APDL Mechanical . The displacement constraint is modelled as a fixed support acting on the cover.
The boundary conditions are loaded as external data by using the results of the CFD pressure acting at the internal surface. It is important to underline that the nodes position inside the moving fluid domain change at every time step.
In this paper, the authors applied to the gear pump case, instead of the experimentally acquired data described in previous work , the resulting displacement data obtained from the structural sub-model.
The results of the two methods are displayed in Fig. 5, in which, is possible to observe the comparison between the experimental/numerical approach (on the left) and the fully integrated approach (on the right).
Figure 5: Displacement of the external case of the pump, on the left, obtained from
the experimental/numerical approach , on the right, obtained with this approach.
Figure 6 clearly compares the trend differences of the vibro-acoustic results. Is important to mention that the obtained sound power (in blue) is considered not yet satisfying but the curve, with exception of the central interval of frequencies, is approaching the benchmark obtained in  (red line) even if the module is different.
Figure 6: Comparison of the sound power calculated between experimental/numerical
approach presented in  (red) and the present model (blue).
This paper describes a first full integrated approach to the vibro-acoustic fluid-structural methodology to predict the noise field emitted by an external gear pump. Many future refinements are scheduled in order to obtain more accurate results. Future adjustments will allows us to create an accurate effective multiphysics aero-fluid-structural approach.