van Bpm Bart Esch

Performance and Radial Loading of a Mixed-Flow Pump Under Non-Uniform Suction Flow

Many centrifugal pumps have a suction velocity profile, which is nonuniform, either by design like in double-suction pumps, sump pumps, and in-line pumps, or as a result of an installation close to an upstream disturbance like a pipe bend. This paper presents an experimental study on the effect of a nonuniform suction velocity profile on performance of a mixed-flow pump and hydrodynamic forces on the impeller. In the experiments, a newly designed dynamometer is used, equipped with six full Wheatstone bridges of strain gauges to measure the six generalized force components. It is placed in between the shaft of the pump and the impeller and corotates with the rotor system. A high accuracy is obtained due to the orthogonality of bridge positioning and the signal conditioning electronics embedded within the dynamometer. The suction flow distribution to the pump is adapted using a pipe bundle situated in the suction pipe. Results of measurements show the influence of the suction flow profile and blade interaction on pump performance and forces. Among the most important observations are a backward whirling motion of the rotor system and a considerable steady radial force.

Direct numerical simulation of the motion of particles in rotating pipe flow

In this paper the motion of particles in rotating pipe flow is studied for various flow cases by means of direct numerical simulation. Compared to flow in a non-rotating pipe, the Navier–Stokes equation contains as only extra term the Coriolis force when the equation is considered in a rotating frame of reference. Particles in the flow also experience a centrifugal force, which drives them to one side of the wall of the pipe. The flow is characterized by two Reynolds numbers for the mean axial velocity and the rotation rate, respectively. Among the cases studied are one in which the flow without rotation would be laminar and rotation leads to turbulence and another one for which Poiseuille flow is unstable but instead of transition to a turbulent state, a time-dependent laminar flow results. In all cases studied a counter-rotating vortex is present. The simulation results are used to calculate the collection efficiency of the rotational phase separator (RPS) under turbulent flow conditions. The RPS is a device to separate liquid or solid particles from a lighter or heavier fluid by means of centrifugation in a bundle of channels which rotate around a common axis. The results show that, compared to Poiseuille flow, the collection efficiency for larger particles decreases due to the combined action of the vortex and turbulent velocity fluctuations, while it is unchanged for smaller particles.

Fish injury and mortality during passage through pumping stations

An unwanted side effect of pumping stations is that fish suffer from injury and mortality when passing through the pumps and that fish migration is hampered. In recent years, the development of so-called fish-friendly pumping stations has received increasing attention from European governmental institutions and pump manufacturers. In the Netherlands, many field studies have been conducted over the last decade to assess the chances of survival for fish passing through pumps. A clear correlation between observed injury or mortality and, for example, flow rate, shaft speed, or pump type could not be established. This paper presents a new analysis of these field studies. It uses American studies on the biological criteria for fish injury, the most important of which are pressure changes, shear forces, and mechanical injury. A blade strike model is adapted to fish passing through centrifugal pumps of radial, mixed-flow, and axial type. It reveals the relation between fish injury and the type of pump, its size, shaft speed, and pressure head. The results correlate fairly well with experiments. The flow through a typical mixed-flow pump is calculated using computational fluid dynamics (CFD). The results show that pressure fluctuations and shear forces are not likely to add much to fish mortality. Guidelines for the design and selection of fish-friendly pumps are given with the introduction of two new dimensionless numbers: the blade strike probability factor and the blade strike velocity factor. It shows that fish-friendliness of pumps decreases with increasing specific speed value.

The turbulent rotational phase separator

The Rotational Phase Separator (RPS) is a device to separate liquid or solid particles from a lighter or heavier fluid by centrifugation in a bundle of channels which rotate around a common axis. Originally, the RPS was designed in such a way that the flow through the channels is laminar in order to avoid eddies in which the particles become entrained and do not reach the walls. However, in some applications the required volume flow of fluid is so large, that the Reynolds number exceeds the value for which laminar Poiseuille flow is linearly stable. Depending on the Reynolds numbers the flow can then be turbulent, or a laminar time-dependent flow results. In both cases a counter-rotating vortex is present, which might deteriorate the separation efficiency of the RPS. This is studied by means of direct numerical simulation of flow in a rotating pipe and particle tracking in this flow. The results show that the collection efficiency for larger particles decreases due to the combined action of the vortex and turbulent velocity fluctuations, while it is unchanged for smaller particles.

Heat Transfer during Growth of a Boiling Bubble on the Wall in Turbulent Channel Flow

Heat transfer to a growing boiling bubble at a plane wall is complicated because of a microlayer between vapor and solid, convection and diffusion and the interaction of flow and heat transfer in the wall. However, typical bubble growth histories [1] and heat flow rate histories [2] are known from experiments. This allows to decouple the growth of a vapor bubble from its effect on temperatures and to consider the bubble as a distribution of heat sinks. One of the important issues to be addressed is the extent to which turbulent fluid velocity fluctuations affect bubble growth. Here, this is investigated by means of DNS of turbulent flow and heat in the presence of a bubble. The geometry is a plane channel, where on both walls a heat flux is supplied. The temperature is split into a periodic part and a part which varies linearly with streamwise coordinate and matches the energy supplied at the walls.