Flow Characteristics in Rectangular Ducts with a Sharp 180-Degree Turn(Effect of Turn Clearance)

Numerical analysis of turbulent flow separation in a rectangular duct with a sharp 180‐degree turn by algebraic Reynolds stress model

“…This turbulent flow is characterized by the large-scale separated flow generated after the sharp turn. The calculated results are compared quantitatively with the experimental data measured by Nakayama et al [8] to confirm the validity of the proposed method. Moreover, the application of the wall function method to the separated flow is examined by replacing the log-law velocity profile based on the flow conditions with and without a separated flow.…”

“…The introduction of ribs in the straight sections not only reduces the size of the separation bubble along the inner wall of the U-bend by raising the turbulence levels at the bend entry but also causes the formation of an additional separation bubble over the first rib interval along the outer wall, downstream from the bend exit. Recently, Nakayama et al [8] reported in detail the measurement results for a turbulent flow in a rectangular duct with a sharp 180-degree turn, including the distributions of Reynolds stresses. They measured the velocity profiles of the mean velocity in the separated region and the distributions of Reynolds stress, which develop along the stream direction, using laser-Doppler anemometry.…”

“…In contrast, few numerical or experimental results have been reported related to turbulent separation, including Reynolds stress. An experimental study was conducted on the flow structure with separation in rectangular channels with a sharp 180-degree turn by Nakayama et al [8]. The mean and fluctuation velocities in three directions, including the separated region, were measured in detail using laserDoppler anemometry at a Reynolds number of 35 000.…”

“…Based on the above-mentioned studies, the main purpose of the present thesis is to predict numerically the turbulent flow in a rectangular channel with a sharp turn, as reported by Nakayama et al [8], in order to estimate the validity of an algebraic Reynolds stress model. In addition, the wall function method, which is used to set the boundary conditions for the turbulent energy and dissipation, is examined.…”

“…Figure 1 shows schematic diagrams of rectangular channels with sharp 180-degree turns that are selected as numerical objects in this calculation. Nakayama et al [8] measured the turbulent flow including a separated flow in these channels in detail, using a laser-Doppler anemometer. They presented three types of experimental data that were measured for varying channel width, which is defined as the distance between the outer and the inner walls at a sharp turning duct, i.e.…”