Experimental and Numerical Investigations of a Turbulent Flow Behavior in Isolated and Nonisolated Conical Diffusers

Abstract

In some industrial processes, and especially in agrofood industries, the cleaning in place mechanism used for hydraulic circuits plays an important role. This process needs a good knowledge of the hydrodynamic flows to determinate the appropriate parameters that assure a good cleaning of these circuits without disassembling them. Generally, different arrangements are present in these hydraulic circuits, such as expansions, diffusers, and elbows. The flow crossing these singularities strongly affects the process of cleaning in place. This work is then a contribution to complete recent studies of “aliments quality security” project to ameliorate the quality of the cleaning in place. It presents experimental and numerical investigations of a confined turbulent flow behavior across a conical diffuser (2α=16 deg). The role of a perturbation caused by the presence of an elbow in the test section, upstream of the progressive enlargement, was studied. The main measurements were the static pressure and the instantaneous velocity fields using the particle image velocimetry (PIV). Post-processing of these PIV measurements were adopted using the Γ2 criterion for the vortices detection and the proper orthogonal decomposition (POD) technique to extract the most energetic modes contained in the turbulent flow and to the turbulent flow filtering. A database has been also constituted and was used to test the validity of the most models of turbulence, and in particular, a variant of the shear stress transport (SST) model.

Study on reconstruction and prediction methods of pressure field on blade surfaces for oil-filling process in a hydrodynamic retarder

“…As typical hydrodynamic transmission component, hydrodynamic retarders are similar to torque converters in terms of the structure and working principle. So, due to the good performance of the model in adverse pressure gradients along with separating flow and high stability in viscous simulations, the SST model was employed in the steady-state and transient-state analysis (Aloui et al, 2011). No-slip boundary conditions were adopted for viscous flow in the CFD model.…”

Experimental and Numerical Investigations Using Lattice Boltzmann Method to Study Shedding Vortices in an Unsteady Confined Flow Around an Obstacle

“…Known under the name of the Q criterion it was proposed by Hunt et al [38]. It can be interpreted by a balance between the rotation rate and the strain rate [39][40]. It should be noted that the distribution of these vortices is different from the infinite medium case.…”

Overview on the hydrodynamic conditions found in industrial systems and its impact in (bio)fouling formation

“…Even under laminar flow, flow disturbances are higher for increasing Re. In sudden contraction or expansion sections, the fluid velocity is affected by changing the pipe diameter [134]. Georgantopoulou [128] verified that longer recirculation zones occurred for increasing Re in an abrupt expansion.…”

“…In fact, Simunic et al [44] verified that in dead-end zones, fouling was not affected by fluid flushing (high turbulence from high fluid velocity) that was typical for the main pipe. Several studies identified critical areas for fouling formation such as the regions closed to corners and baffles [59,75,104] and header section [102] in HE, regions closed to expansions/contractions [110,120], angles [128,134], elbows [112,133], and valves [12,114] in distribution networks, and regions closed to corners in the bottom [154], and baffles in the tank wall [165] in STRs. In addition of being prone for fouling phenomena, dead-end zones affect CIP efficacy, compromising the process and product quality, and increase operating and maintenance costs [12].…”