Diffuser (thermodynamics)

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

Developing an empirical model for ducted tidal turbine performance using numerical simulation results

Abstract: This article studies the effects of viscous loss, flow separation, and base pressure for ducted turbine designs using computational fluid dynamics (CFD) simulations. Analytical model coefficients for inlet and diffuser efficiency and base pressure coefficient parameterize these effects and have been identified from CFD results. General trends are that the inlet efficiency is nearly unity for the simulated designs; the diffuser efficiency has a significant impact on per- formance and is degraded by flow separation; and that the base pressure effect can provide a significant performance enhancement. Geometric features influencing each of the aforemen- tioned parameters are identified and a regression-based model has been developed to predict ducted turbine performance.

Apparatus for increasing the flow speed of a medium and for recovering its kinetic energy

Abstract: Apparatus for increasing the flow speed of a medium such as air and for recovering its kinetic energy, comprising a series of concentrical, substantially symmetrically arranged annular members separated by annular slots, said members in the direction towards length axis of the apparatus, which coincides with the flow direction of the medium, having successively and substantially symmetrically decreasing dimensions in the direction of said length axis to the formation of an inlet opening wherein said annular members have curved leading edges with intermediary annular slots for removal of turbulent medium, and to the formation of an outlet opening acting as a diffuser for the medium, wherein said annular members are successively thinner to the formation of sharp edges directed outwards from the length axis of the apparatus; the kinetic energy of the medium being recovered by conventional means. Separate accelerator means are also provided.

A Study of Impeller-Diffuser-Volute Interaction in a Centrifugal Fan

Abstract: This paper reports velocity measurement data in the interaction region between the impeller and vaned diffuser and the results of numerical flow simulation of the whole machine (impeller vaned diffuser and volute) of a single stage centrifugal fan. Two-dimensional instantaneous velocity measurement is done using particle image velocimetry (PIV). Numerical simulation of impeller-diffuser-volute interaction is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady calculation and a rotor-stator simulation model is used for the unsteady calculation using the steady results as an initial guess. The simulation results show that the separated flow regime near the diffuser hub extends to the volute. Comparison between the unsteady computation and those of measurement indicates that the rotor/stator model employed in the simulation predicts essential characteristics of unsteady flow in the centrifugal fan. However, quantitative agreement remains rather poor.

Unsteady Flow in a Turbocharger Centrifugal Compressor: Three-Dimensional Computational Fluid Dynamics Simulation and Numerical and Experimental Analysis of Impeller Blade Vibration

Abstract: Experimental investigations on a single stage centrifugal compressor showed that measured blade vibration amplitudes vary considerably along a constant speed line from choke to surge. The unsteady flow has been analyzed to obtain detailed insight into the excitation mechanism. Therefore, a turbocharger compressor stage impeller has been modeled and simulated by means of computational fluid dynamics (CFD). Two operating points at off-design conditions were analyzed. One was close to choke and the second one close to the surge line. Transient CFD was employed, since only then a meaningful prediction of the blade excitation, caused by the unsteady flow situation, can be expected. Actually, it was observed that close to surge a steady state solution could not be obtained; only transient CFD could deliver a converged solution. The CFD results show the effect of the interaction between the inducer casing bleed system and the main flow. Additionally, the effect of the nonaxisymmetric components, such as the suction elbow and the discharge volute, was analyzed. The volute geometry itself had not been modeled. It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the exit of the vaned diffuser to simulate the volute. Volute and suction elbow impose a circumferentially asymmetric flow field, which induces blade excitation. To understand the excitation mechanism, which causes the measured vibration behavior of the impeller, the time dependent pressure distribution on the impeller blades was transformed into the frequency domain by Fourier decomposition. The complex modal pressure data were imposed on the structure that was modeled by finite element methods (FEM). Following state-of-the-art calculations to analyze the free vibration behavior of the impeller, forced response calculations were carried out. Comparisons with the experimental results demonstrate that this employed methodology is capable of predicting the impeller 's vibration behavior under real engine conditions. Integrating the procedure into the design of centrifugal compressors will enhance the quality of the design process.

Design Method of Controllable Blade Angle and Orthogonal Optimization of Pressure Rise for a Multiphase Pump

Abstract: The hydraulic design method of controllable blade angle for rotodynamic multiphase pump with impeller and diffuser is proposed. The distribution of blade angle along the meridional streamline is governed by the normalized fourth-order and first-order polynomial function for impeller and diffuser, respectively. The orthogonal optimization method with five factors and four levels is employed by numerical simulation to optimize the geometry parameters, including the shroud angle at the leading and trailing edge βIs0, βIs1, the blade difference at inlet ∆βI0, and the coefficients at hub and shroud kh, ks. According to orthogonal analysis, the influence of each factor on pressure rise is estimated, and the optimization values of for those parameters are determined. The pressure rise of optimization multiphase pump is increased by 12.8 kPa in comparison of the base pump. Results show that the distributions of gas volume fraction (GVF) and the pressure become more uniform after optimization, which improves the transporting performance of the multiphase pump.