VORTEX2 Research Articles

Numerical Simulation and Analysis of the Flow Characteristics of the Roof-Attached Vortex (RAV) in a Closed Pump Sump

Unsteady numerical simulation and visual experiment are used to reveal the formation mechanism of the roof-attached vortex (RAV) on the roof of the closed sump of a pumping station. The results show that RAVs mainly occur between the pump device and the rear wall of the closed sump. In the 10th period of impeller rotation, there are 2 RAVs at the roof. V1 (Vortex 1 in numerical simulation) is located directly behind the water pump unit, and V2 (Vortex 2 in numerical simulation) is close to the right wall. Significantly, the vorticity intensity at the V1 vortex core increases with the rotation of the impeller. Vtest1 (Vortex 1 in test) and Vtest2 (Vortex 2 in test) are two RAVs observed in the experiment, which are highly consistent with the unsteady numerical simulation V1 and V2. Comparing the vorticity intensity of the roof, rear wall, and sidewall, it can be seen that the maximum vorticity intensity on the roof is more significant than that on the rear wall and both sides of the wall. The roof is more likely to induce vortex. When the RAVs on the roof occur, the pressure in the middle of the bell mouth is lower than that on the sidewall, and the velocity is higher. At 2/5 T, the blade is in the low-pressure zone. The velocity distribution uniformity and velocity weighted average angle at the bell mouth also decreased. The RAVs enter the pump after being generated, which is the most harmful to the safe and stable operation of the pump. The study can provide theoretical guidance for the optimal design of the closed sump.

Study on flow separation and transition of the airfoil in low Reynolds number

As typical flow characteristics in a low Reynolds number, laminar separation bubbles (LSBs) and transition to turbulence over airfoils have been extensively studied in recent years. In order to analyze their flow mechanism, numerical investigation using the finite volume method to solve the Reynolds averaged Navier-Stokes equations with a transition Shear Stress Transport (SST) four-equation transition model is performed in this work, combined with the experimental study facilitated by the oil film interferometry technique. Specifically, the transition SST four-equation transition model is solved to simulate the separation location and LSB structure at low Reynolds numbers on a Wortmann FX63-137 airfoil. Good agreement is obtained between the numerical simulation and experimental measurements regarding the separation, transition and reattachment location, aerodynamic coefficients, and overall flow structures. At higher Reynolds numbers of 200 000 and 300 000, similar bubble structures on the airfoil surface are observed, and the location of the bubble moves toward the leading edge of the airfoil by increasing the angle of attack. However, in Reynolds numbers ranging from 300 000 to 500 000, significant changes of the laminar flow separation structures emerge. The flow structure changes from the classical laminar separation bubble to the nonclassical separation flow structure that is composed of a major vortex 1(V1) and a minor vortex 2(V2). Due to the small distance between V1 and V2, it is difficult to distinguish the delicate structure of the two separation bubbles from the classical laminar separation bubble by the experimental method.