Analysis of the Flow Force Compensation in Relief Valves With Conical Poppet

The paper deals with experimental tests and numerical simulations (3D and 0D fluid-dynamic modelling) of a conical poppet pressure relief valve with flow force compensation. The aim of the study was to realize a dynamic model of the valve, able to consider the effect of the pressure force, which arises downstream the metering edge and is determined by both the flow forces and the pressure recovery on the flow deflector. Starting from a 3D-CFD model, it was possible to study the interaction between the poppet opening and the pressure field, in order to evaluate the total pressure force as a function of the poppet displacement. The contribution of the pressure recovered on the deflector was separated from the traditional flow force and then parametrized as a function of some geometric features. It was then possible to develop a 0D fluid-dynamic model that is suitable not only for the considered valve but also for valves with similar geometries. Lastly, the model was validated using experimental data acquired on test bench for three different valves. The comparison of the predicted flow-pressure characteristics with the experimental ones indeed showed a good result matching. This model can also lead towards design considerations to study the behaviour of a larger number of valve geometries.

Local Scour Near Flexible Flow Deflectors

Rigid flow deflectors are usually used on water flow beds to protect engineering structures such as breakwater in coasts and to regulate flow routes in open channels. To reduce its side-effects, i.e., local scour at the toe of deflectors, a flexible flow deflector is proposed, and the corresponding local scour was investigated in this study. A flume experiment was conducted to investigate local scour. To show the advantage of flexible deflectors, a control experimental test was also conducted using a traditional rigid deflector under the same blockage area configuration and the same flow conditions. The flow field near the flexible deflector was also measured to reveal the local flow field. The results show that the bed-scour develops near the toe edges of both flexible and rigid deflectors, but the maximum and averaged scour depths for the flexible deflector are smaller. This advantage of flexible deflector in scour depth is mainly caused by its prone posture, which induces the upward stretching and enlarging horizontally rotating vortex and the upward shifted vertically rotating vortex. The former dissipates more turbulent energy and the latter results in smaller bed shear stress, which lead to smaller scour depth directly. In addition, the up- and down-swaying movement of the flexible deflector can also assistant to dissipate more turbulent energy, thereby damping the intense of the horseshoe vortices and thus weakening scour depth as well. The results of this study provide an elementary understanding on the mechanisms of a flexible flow structure and an alternative deflector-device to reduce scour depth.

MINIMIZING BED SCOUR INDUCED BY SHIP BOW-THRUSTERS BY USING QUAY WALL FLOW DEFLECTOR

Recently, the combination of larger bow-thrusters installed with vessels have created higher levels of bed scour action affecting the berthing structure and its overall stability. Therefore, the bed near a quay wall structure must have sufficient strength by placing a bed protection which may cause the cost of the project to rise. This research is carried out to investigate experimentally the effect of modifying the geometry of the quay wall surface on minimizing bed scour. This is done by inserting flow deflectors within the longitudinal direction of the wall surface in order to deflect/minimize the water jet affecting the bed near the quay wall. Experimental tests had been carried out for single and triple deflectors. The results showed that the use of flow deflectors achieved a reduction in bed eroded area in front of quay wall face by about 63%, and causes the start point of erosion to move far away from it; this may improve the stability of quay walls. Therefore, the importance of the present study is testing a new possible measure to improve the stability of quay walls by minimizing the scour in front of the wall and to decrease the cost of bottom protection.