Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: the influence of small aspect ratio

Abstract

In this research, the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results of three-dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent stresses are approximated using k-ε model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay at the jet centerline are noted. The velocity vectors of the main flow and the secondary flow are illustrated. Also, effect of aspect ratio on mixing in rectangular cross-section jets is considered. The aspect ratios that were considered for this work were 1:1 to 1:4. The results showed that the jet entrains more with smaller AR. Special attention has been drawn to the influence of the Reynolds number (based on hydraulic diameter) as well as the inflow conditions on the evolution of the rectangular jet. An influence on the jet evolution is found for smaller Re, but the jet is close to a converged state for higher Reynolds numbers. The inflow conditions have considerable influence on the jet characteristics.

On the effect of inflow conditions in simulation of a turbulent round jet

“…Also it should be mentioned that the experiment of Quinn [1] and Quinn and Militzer [21] does not have the same Reynolds number ( [1] in Re = 1.84 × 10 5 and [21] in Re = 2.08 × 10 5 ). This is supported by Malmstrom et al [36], Mi et al [37] and Faghani et al [27,28] who showed that the mean flow quantities are independent of Reynolds number for the Reynolds numbers higher than a critical value. Figure 9 shows the decay of mean streamwise velocity along the centerline for a contoured nozzle in the near-field region.…”

“…But the results of Berg et al [22] show some deviation, especially in the spread of jet and the streamwise velocity profile at the near field of the inlet. Faghani et al [27,28] simulated the flow from different nozzle shapes. In this research, higher turbulence intensity was used to simulate flow through a sharp-edged nozzle.…”

A comparison of three turbulence models for the prediction of parallel lobed jets in perforated panel optimization

“…Recently Faghani et al [22] reported an investigation of the inflow condition of a rectangular turbulent jet on the mean flow properties. A uniform velocity profile at the nozzle exit with two turbulence intensities, i.e.…”

Numerical study of heat and mass transfer in underexpanded sonic free jet

“…Regard to mixing and entrainment phenomenon in free jets and also due to overcoming of inertia forces to viscous forces, gas leakage from tanks has turbulent nature [19]. In numerical modeling using Boussinesq approximation, turbulence terms in momentum equations (Reynolds stresses) get related to gradient of average velocities according to Eq(11) [20,21]:…”

“…TKE is kinematic energy of velocity fluctuations and TI is turbulence intensity which was calculated using Eq (19):…”