A computational parametric study on the development of confluent round jet arrays

Abstract

In this study, Computational Fluid Dynamics (CFD) and response surface methodology is employed in a parametrical investigation of an in-line array of confluent round jets. Confluent round jet arrays are common within several fields of engineering, as detailed knowledge of the flow field development of confluent round jets is of great importance to design engineers working with, for example, chemical mixing, multiple jet burners, waste water disposal systems or ventilation supply devices. In this paper, five independent factors affecting flow field development are investigated with a multi-variable approach using a Box–Behnken design method.The results include decay of maximum velocity, turbulence intensity, location of merging and combined points and development of volumetric flow rate. Dimensionless nozzle spacing, S/d0, is an important design parameter and has a large impact on several properties, such as merging and combined points, decay of maximum velocity, and development of turbulence intensity. Other factors, such as the number of jets per row and inlet velocity, are also of importance. The analysis of decay in maximum velocity led to the definition of a new zone of development, referred to as the Confluent Core Zone (CCZ), as its behaviour is reminiscent of the potential core of a single jet. The CCZ has uniform velocity, lacks considerable decay in streamwise velocity and has a rather low turbulence intensity. The CCZ has a characteristic footprint in confluent round jet arrays, and its properties are investigated in detail.The development of volumetric flow can be divided into two regions. The initial region, close to the nozzles, features a high entrainment but decreasing entrainment rate. As the jets combine, the entrainment rate is lower, but rather constant. While S/d0 is generally an important design parameter, there is no direct correlation between S/d0 and entrainment rate of the combined jet.