A numerical study of pulsating flow behind a constriction

1995 ◽  
Vol 301 ◽  
pp. 203-223 ◽  
Author(s):  
Moshe Rosenfeld
Keyword(s):  
Flow Field ◽  
Strouhal Number ◽  
Numerical Study ◽  
Pulsating Flow ◽  
Vortical Flow ◽  
Incoming Flow ◽  
Core Flow ◽  
Wide Range ◽  
Constricted Channel

The flow field behind a constricted channel is studied numerically. A pulsating incoming flow with a non-vanishing mean is imposed at the entrance and the flow field is investigated for a wide range of Reynolds and Strouhal numbers (1500 > Re > 45, 12 > St > 0.01). In most cases (except at the two ends of the Strouhal number regime or for Re < 90), propagating vortices are found downstream of the constriction with a wavy core flow between them. The size and number of coexisting vortices depend on St but less on Re. The strength and structure of the vortical regions depend on both Re and St. The formation of the vortices is discussed for the various St regimes and the characteristics of the vortical flow are described.

Film Cooling From Short Holes With Sister Hole Influence

2012 ◽  
Author(s):  
Marc J. Ely ◽  
B. A. Jubran
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Film Cooling ◽  
Computational Analysis ◽  
Numerical Study ◽  
Vortical Flow ◽  
Injection Hole ◽  
Hole Configuration ◽  
Adiabatic Effectiveness ◽  
Structure Research

This paper reports a computational analysis on the effect of sister hole control on film cooling from short holes. The proposed method includes surrounding a primary injection hole by two or four smaller sister holes to actively maintain flow adhesion along the surface of the blade. A numerical study using the realizable k-ε turbulence model led to the determination that the use of sister holes significantly improves adiabatic effectiveness by countering the primary vortical flow structure. Research was carried out to determine the optimum hole configuration, arriving at the conclusion that placing sister holes slightly downstream of the primary injection hole improves the near-hole effectiveness, while placing sister holes slightly upstream of the primary hole improves downstream effectiveness. Similar results were found in evaluating both long and short hole geometries with a significantly less coherent flow field arising from the short hole. However, on the whole, the sister hole approach to film cooling was found to offer viable improvements over standard cooling regimes.

scholarly journals SYNCHRONIZATION OF PENDULUMS (NUMERICAL STUDY)

2021 ◽  
Vol 6 (3) ◽  
pp. 16-25
Author(s):  
Robert A. Sunarchin ◽  
Pavel V. Petrov
Keyword(s):  
Strouhal Number ◽  
High Efficiency ◽  
Numerical Study ◽  
Auxiliary Problem ◽  
Free Vibrations ◽  
Mutual Synchronization ◽  
Wide Range

This paper presents the results of a numerical study of synchronization of pendulums, chronometers, and mechanical clocks suspended from a common movable beam. An auxiliary problem is considered about the oscillations of a pendulum with a swinging weight, then the mutual synchronization of free vibrations of two and four pendulums (and pendulums with the supply of a moment pulse-clock) on a common movable spring-loaded beam. It is shown that in the considered simplest configuration, mutual synchronization (equality of frequencies or oscillation periods) is performed with high efficiency. The frequency of synchronized oscillations of the pendulums is close to the frequency of vibrations of the platform in a wide range of changes in its rigidity. The degree of connectivity of pendulums and synchronization of their oscillations is determined by the Strouhal number. Synchronization of clocks does not guarantee the accuracy of their movement, which is achieved only when the Strouhal number is equal to one.

Experimental and Numerical Investigation of the Flow in a Low-Pressure Industrial Steam Turbine With Part-Span Connectors

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Markus Häfele ◽  
Christoph Traxinger ◽  
Marius Grübel ◽  
Markus Schatz ◽  
Damian M. Vogt ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Numerical Study ◽  
Three Dimensional ◽  
Low Pressure ◽  
Operating Conditions ◽  
Engineering Practice ◽  
Cfd Model ◽  
Wide Range ◽  
The Impact

An experimental and numerical study on the flow in a three-stage low-pressure (LP) industrial steam turbine is presented and analyzed. The investigated LP section features conical friction bolts in the last and a lacing wire in the penultimate rotor blade row. These part-span connectors (PSC) allow safe turbine operation over an extremely wide range and even in blade resonance condition. However, additional losses are generated which affect the performance of the turbine. In order to capture the impact of PSCs on the flow field, extensive measurements with pneumatic multihole probes in an industrial steam turbine test rig have been carried out. State-of-the-art three-dimensional computational fluid dynamics (CFD) applying a nonequilibrium steam (NES) model is used to examine the aerothermodynamic effects of PSCs on the wet steam flow. The vortex system in coupled LP steam turbine rotor blading is discussed in this paper. In order to validate the CFD model, a detailed comparison between measurement data and steady-state CFD results is performed for several operating conditions. The investigation shows that the applied one-passage CFD model is able to capture the three-dimensional flow field in LP steam turbine blading with PSC and the total pressure reduction due to the PSC with a generally good agreement to measured values and is therefore sufficient for engineering practice.

A Parametric Numerical Study of the Effects of Inlet Swirl Distortion on a Transonic Compressor Stage

2013 ◽  
Author(s):  
Taieb Ben Sghaier ◽  
Ahad Mehdi ◽  
Vassilios Pachidis ◽  
David MacManus
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Underlying Mechanism ◽  
Aerodynamic Characteristics ◽  
Vortical Flow ◽  
Compressor Stage ◽  
Significant Drop ◽  
Transonic Compressor ◽  
Wide Range ◽  
Compressor Performance

The ingestion or manifestation of a vortical flow can have dramatic effects on an aero engine. It is therefore imperative to quantify these effects and understand their underlying mechanism. This numerical study analyses the response of a transonic compressor stage to the ingestion of different streamwise vortical distortions using steady-state CFD. The vortex is described using a number of features, which are varied and combined together in order to generate a wide range of different swirl disturbances. The initial aim of this research is to identify the vortex features which have the highest impact on compressor performance. A numerical model of a compressor stage is generated which enables prescribed vortical flows to be imposed at the domain inlet. The method is validated against experimental data which was obtained under clean, undistorted conditions. The response of the compressor following the ingestion of a vortex is assessed both in terms of overall compressor performance parameters as well as more detailed aerodynamic characteristics. The results show that the compressor is sensitive to the vortex magnitude, core size, polarity and radial location. Furthermore, co-rotating, high-strength vortices which are ingested in the near-hub region cause the most significant drop in pressure ratio and corrected mass flow. In contrast, counter-rotating vortices cause little change in compressor performance. Overall, the work shows that modest swirl distortions can have a notable impact on the compressor performance and stability, and highlights the growing need to develop methods and an understanding of how this class of distortion can be evaluated during the engine design phase.

Experimental and Numerical Investigation of the Flow in a LP Industrial Steam Turbine With Part-Span Connectors

2015 ◽  
Author(s):  
M. Häfele ◽  
C. Traxinger ◽  
M. Grübel ◽  
M. Schatz ◽  
D. M. Vogt ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Numerical Study ◽  
Resonance Condition ◽  
Three Dimensional ◽  
Measurement Data ◽  
Detailed Comparison ◽  
Operating Conditions ◽  
Engineering Practice ◽  
Wide Range

An experimental and numerical study on the flow in a three stage low pressure (LP) industrial steam turbine is presented and analyzed. The investigated LP section features conical friction bolts in the last and a lacing wire in the penultimate rotor blade row. These part-span connectors (PSC) allow safe turbine operation over an extremely wide range and even in blade resonance condition. However, additional losses are generated which affect the performance of the turbine. In order to capture their impact on the flow field, extensive measurements with pneumatic multi-hole probes in an industrial steam turbine test rig have been carried out. State-of-the-art three-dimensional CFD applying a non-equilibrium steam (NES) model is used to examine the aero-thermodynamic effects of the PSC on the wet steam flow. A detailed comparison between measurement data and CFD results is performed for several operating conditions. The investigation shows that the applied CFD model is able to capture the three-dimensional flow field in LP steam turbine blading with PSC and the total pressure reduction due to the PSC with a generally good agreement to measured values and is therefore sufficient for engineering practice.

Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

2011 ◽  
Author(s):  
Dipanjay Dewanji ◽  
Arvind G. Rao ◽  
Mathieu Pourquie ◽  
Jos P. van Buijtenen
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Numerical Study ◽  
Reverse Flow ◽  
Direct Injection ◽  
Flow Characteristics ◽  
Droplet Breakup ◽  
Reacting Flow ◽  
Lean Direct Injection ◽  
Wide Range

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.

Energy Redistribution Between the Mean and Pulsating Flow Field in a Separated Flow Region

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Sharul S. Dol ◽  
M. Mehdi Salek ◽  
Robert J. Martinuzzi
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Shear Layer ◽  
Strouhal Number ◽  
Coherent Structures ◽  
Pulsating Flow ◽  
Reynolds Stresses ◽  
Velocity Correlation ◽  
Energy Redistribution ◽  
The Mean

One of the main features of the backward-facing step (BFS) low frequency pulsatile flow is the unsteadiness due to the convection of vortical (coherent) structures, which characterize the flow dynamics in the shear layer. The physics of the flow field is analyzed by looking at energy redistribution between the mean and pulsating flow field obtained via a particle image velocimeter (PIV) using the concept of a triple decomposition. The total fluctuating kinetic budget is calculated and discussed for a mean Reynolds number of 100 and for 0.035 ≤ St ≤ 2.19. The effects that these coherent structures have on the fluctuating kinetic energy production, dissipation, and transport mechanism are examined. The results provide insight into the physics of the flow and suggest reasons for vortex growth and decay. Fluctuating kinetic energy is generally produced at the separated shear layers and transported towards the core flow and then to the upper and lower walls where viscosity dissipates the energy. The remaining energy is transported streamwise and decays as it is convected downstream (St = 0.4 and 1 cases). It was also found that the pressure-velocity correlation diffusion plays a significant role in the transport of kinetic energy and Reynolds stresses, especially in the separated shear layer. More energy was dissipated at the walls for the high Strouhal number case St = 2.19 due to the transverse pressure diffusion term being increasingly dominant. This could be the reason why the convected primary vortices were much smaller in size and weaker with no upper wall vortices formed at this pulsation Strouhal number. The shear production for St = 0.035 was very minimal; thus, the vortices died down quickly even before the shedding could happen. Finally, the pressure-strain correlation term was found to be significant in redistributing the kinetic energy from u-component to v-component.

Numerical Study of the Combined Free-Forced Convection and Mass Transfer Flow Past a Vertical Porous Plate in a Porous Medium with Heat Generation and Thermal Diffusion

2006 ◽  
Vol 11 (4) ◽  
pp. 331-343 ◽  
Author(s):  
M. S. Alam ◽  
M. M. Rahman ◽  
M. A. Samad
Keyword(s):  
Mass Transfer ◽  
Flow Field ◽  
Differential Equations ◽  
Forced Convection ◽  
Heat Generation ◽  
Numerical Study ◽  
Porous Plate ◽  
Integration Scheme ◽  
Suction Parameter ◽  
Transfer Flow

The problem of combined free-forced convection and mass transfer flow over a vertical porous flat plate, in presence of heat generation and thermaldiffusion, is studied numerically. The non-linear partial differential equations and their boundary conditions, describing the problem under consideration, are transformed into a system of ordinary differential equations by using usual similarity transformations. This system is solved numerically by applying Nachtsheim-Swigert shooting iteration technique together with Runge-Kutta sixth order integration scheme. The effects of suction parameter, heat generation parameter and Soret number are examined on the flow field of a hydrogen-air mixture as a non-chemical reacting fluid pair. The analysis of the obtained results showed that the flow field is significantly influenced by these parameters.

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