The behavior of the flow in a vertical semi-axial mixed flow pump has been analyzed by numerical flow simulations of the entire stage, and the results have been compared to test data. As the flow is expected to be unsteady at part load in such a pump, the steady-state simulations were complemented with unsteady flow simulations of the entire machine at one part load operating point. Pressure measurements at different locations in the casing of the pump provided valuable data for the validation of the calculated pressure head. This paper shows that the pump characteristic can be quite accurately predicted from full load to part load by modern numerical tools. Simulations of the unsteady flow, which use much more computer resources, are also feasible in an industrial environment and yield detailed information about the flow patterns and pressure fluctuations in the pump.

The use of computational fluid dynamics (CFD) to model the operation of thermal-spray processes has gained interest in the thermal-spray community, able to provide an understanding as to how a process functions, and better how to make a process work better. Advancements to the science of modeling now permits the ability to create a comprehensive model of a plasma gun that not only simulates the dynamics of the gas, but also the mechanics of arcs (plasma), thermodynamics, and entrained particulates to form a nearly complete model of a working thermal-spray process. Work presented includes the methods and procedures used to validate the model to a Sulzer Metco TriplexPro TM -200 plasma gun and exploration of the operating regime to give an in depth and insightful look into the physics behind the operation of a triple-arc cascaded plasma gun.

Use of a comprehensive validated computer model of a thermal spray process enables an ability to improve, optimize, and fine-tune the performance of that thermal spray process. A validated model of the Sulzer Metco TriplexPro TM 200 plasma gun has been used to improve the performance of the actual gun in terms of enhancing gas flow dynamics, thermal management, and overall performance in terms of a robust design. Internal changes to the gun geometry using the model have extended the life of the hardware. In addition the model has permitted the investigation of the fundamental operation of the gun, specific to the behavior and path of the arcs, as well as the ability to operate the plasma gun, under simulation, in operating regimes that currently cannot be supported by the physical hardware. The model has been run at gas pressures above 1.4 Mpa and/or voltages above 300 V that currently cannot be obtained with the physical hardware due to equipment limitations to evaluate the potential to extend the operating window of the Sulzer Metco TriplexPro TM 200 gun beyond current levels in terms of particle velocity and temperature. The end result is an improved process tool for applying thermal spray coatings ranging from ceramics applied at high particle temperature and low particle velocities to carbides and alloys applied at lower temperatures and higher velocities.

This paper describes an investigation into the use of CFD for highly loaded pump diffuser flows. A reliable commercial Navier-Stokes code with the standard k-ε turbulence model was used for this work. Calculations of a simple planar two-dimensional diffuser demonstrate the ability of the k-ε model to predict the measured effects of blockage and area ratio on the diffuser static pressure recovery at low loading levels. At high loading levels with flow separation the k-ε model underestimates the blockage caused by the recirculation in the flow separation region and overestimates the pressure recovery in the diffuser. Three steady-state calculations of a highly loaded vaned diffuser of a medium specific speed pump have been carried out using different inlet boundary conditions to represent the pump outlet flow. These are compared to LDA measurement data of the flow field and demonstrate that although the Navier-Stokes code with the standard k-ε turbulence model is able to predict the presence of separation in the flow, it is not yet able to accurately predict the static pressure rise of this highly loaded pump diffuser beyond the flow separation point.

This paper describes experimental and computational work to examine the unsteady flowfield in the vaned diffuser of a medium specific speed pump. The time periodic flowfield in the diffuser has been examined experimentally with laser optical techniques and with unsteady pressure transducers. The flow has been computed with a general purpose Navier-Stokes CFD code, whereby the unsteady effects have been simulated by a time periodic inlet profile which translates across the diffuser inlet and represents the wakes and potential interaction from the impeller. Comparisons of a steady simulation with time-average inlet conditions, an unsteady simulation with a time periodic inlet profile and the time-average of the unsteady simulation are used to validate the code developments and to examine features of the unsteady flow through the diffuser. Comparisons with experimental data identify that this simple computational model with a time periodic inlet profile is able to simulate the convection and decay of disturbances passing through the diffuser.