Diffuser (thermodynamics)

About: Diffuser (thermodynamics) is a research topic. Over the lifetime, 6731 publications have been published within this topic receiving 54738 citations.

Flow-Feedback Method for Mitigating the Vortex Rope in Decelerated Swirling Flows

Abstract: When reaction hydraulic turbines are operated far from the design operating regime, particularly at partial discharge, swirling flow instability is developed downstream of the runner, in the discharge cone, with a precessing helical vortex and its associated severe pressure fluctuations. Bosioc et al. (2012, “Unsteady Pressure Analysis of a Swirling Flow With Vortex Rope and Axial Water Injection in a Discharge Cone,” ASME J. Fluids Eng., 134(8), p. 081104) showed that this instability can be successfully mitigated by injecting a water jet along the axis. However, the jet discharge is too large to be supplied with high pressure water bypassing the runner, since this discharge is associated with the volumetric loss. In the present paper we demonstrate that the control jet injected at the inlet of the conical diffuser can actually be supplied with water collected from the discharge cone outlet, thus introducing a new concept of flow feedback. In this case, the jet is driven by the pressure difference between the cone wall, where the feedback spiral case is located, and the pressure at the jet nozzle outlet. In order to reach the required threshold value of the jet discharge, we also introduce ejector pumps to partially compensate for the hydraulic losses in the return pipes. Extensive experimental investigations show that the wall pressure fluctuations are successfully mitigated when the jet reaches 12% of the main flow discharge for a typical part load turbine operating regime. About 10% of the jet discharge is supplied by the plain flow feedback, and only 2% boost is insured by the ejector pumps. As a result, this new approach paves the way towards practical applications in real hydraulic turbines.

Spring powered, portable, hand held suction and blower apparatus

Abstract: A portable, hand held, air suction and blower unit comprising an air inlet assembly with sequentially arranged nozzle, flexible inlet tube, and diffuser, all detachably connected to the front end of the unit body. The diffuser cooperates with the front end of the body to form a bayonet type joint therebetween. An air inlet passage extends rearwardly from the front end of the body to the tangential fan which is journaled at the rear of the body. The fan is powered by a manually wound flat spiral spring, which spring drives the fan through a gear train. An air outlet passage extends forwardly from the fan to an outlet opening also located at the front of the unit body. A removable, pervious receptacle, with an open forward end, is located in the front portion of the air inlet passage and serves to collect particles or objects which are drawn into the body by the flowing air. Furthermore, a flap valve, which is located in the diffuser, allows the particles or objects to pass by and enter into the receptacle when air is being drawn into the body by the fan. The flaps of the valve, however, relax to close off the receptacle from the nozzle when the fan is not operating.

Fluid flow distributor apparatus for gas turbine engine mid-frame section

Abstract: A plenum ( 210 ) in a gas turbine engine mid-frame section ( 200 ) comprises one or more annular flow splitters ( 240 ) spaced from an inboard annular wall ( 232 ) that partition air flow flowing from a compressor into two or more portions of flow having different vectors. This provides for an improved balancing between supplying air to compression chamber intakes more directly and to transitions to aid in convective cooling. When an annular diffuser ( 202 ) is spaced between the compressor and the plenum ( 210 ), the flow splitters ( 240 ) may provide an additional diffusion action. When no annular diffuser is so provided, the flow splitters ( 452, 454, 456 ) are effective to diffuse the air flow. Embodiments include those in which an annular diffuser ( 304 ) is relatively shorter and there is a longer axial expanse in the plenum ( 320 ) for flow splitters ( 350, 352, 354, 356 ).

Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser

Abstract: Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations.The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.

Fluidic actuation for improved diffuser performance

Abstract: A diffuser includes an opening along the diffuser wall for preventing or delaying boundary layer separation of the main flow. The opening may include a curved passageway having a curvature convex relative to the main flow for utilizing the Coanda effect. A gas turbine may include the diffuser with an opening and a centerbody with an opening, each for providing a secondary flow of fluid into the diffuser. The gas turbine may direct fluid from an upstream turbine stage to the opening. A steam turbine may include the diffuser and may situate the opening downstream the diffuser inlet but upstream the location of boundary separation.