Conference Year
2018
Keywords
Computational fluid dynamics, finite element analysis, reciprocating compressors, reed valves
Abstract
Computational fluid dynamics has been increasingly used in the design and analysis of reciprocating compressors over the last several years. One of the major challenges in the use of such tools is the creation of the numerical grid on which the modeled equations are solved. Since these compressors typically consist of many interconnected and moving parts, manual creation of the grid can be labor-intensive. Furthermore, it is necessary that the choice of grid yields a sufficiently resolved solution, so that the numerical error is significantly less than the modeling error. In this work, a small displacement refrigeration compressor is modeled using a numerical grid created with an automatic meshing approach. The grid is then automatically adapted to the flow based on the local flow field variables at each time step. This cut-cell based grid matches the supplied fluid volume exactly and permits general motion of all bounding surfaces. An explicit two-way coupled approach is used to account for the fluid-structure interaction between the deforming reed valves and the flow. The fluid is solved using a finite-volume approach, whereas the solid is solved using a finite-element model. The model is validated in comparison to measured mass flow rate, pressure, temperature, and valve lift for two different operation conditions and two different working fluids, namely R-404a and R-449a. The numerical accuracy of the calculations is demonstrated through an automated grid convergence study, and the effect of the grid and time-step resolution on the pressure pulsations and valve lift is shown. While computations on a relatively coarse grid yield power, mass flow rate, and pressure oscillation frequency comparable to measurements, a finer mesh is required inside the cylinder and in the discharge muffler to predict adequately the amplitude of the pressure fluctuations.