Unsteady Structure and Development of a Row of Impingement Jets, Including Kelvin–Helmholtz Vortex Development

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Li Yang ◽  
Phillip Ligrani ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Static Pressure ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Impinging Jets ◽  
Navier Stokes ◽  
Vortex Generation ◽  
Local Flow ◽  
Layer Parameter

Considered is a cylinder channel with a single row of ten aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady Reynolds-Averaged Navier–Stokes (RANS) solver is employed for predictions of flow characteristics within and nearby the ten impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component vorticity, three-dimensional streamlines, shear layer parameter ψ, and local static pressure. Kelvin–Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin–Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.

Unsteady Structure and Development of a Row of Impingement Jets, Including Shear Layer and Vortex Development: Part 1 — Turbulent Jets

2015 ◽  
Author(s):  
L. Yang ◽  
P. M. Ligrani ◽  
J. Ren ◽  
H. Jiang
Keyword(s):  
Shear Layer ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulent Jets ◽  
Axial Direction ◽  
Impinging Jets ◽  
Local Flow ◽  
Layer Parameter ◽  
Unsteady Rans

Considered is a cylinder channel with a single row of 10 aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady RANS solver is employed for predictions of flow characteristics within and nearby the 10 impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component of vorticity, three-dimensional streamlines, a shear layer parameter, and local static pressure. Kelvin-Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin-Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.

Three-dimensional separated flow structure over a cylinder with a hemispherical cap

1996 ◽  
Vol 324 ◽  
pp. 83-108 ◽  
Author(s):  
T. Hsieh ◽  
K. C. Wang
Keyword(s):  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Horseshoe Vortex ◽  
Navier Stokes ◽  
Water Tunnel ◽  
Separation Sequence ◽  
Vortex Systems ◽  
Good Agreement

Thin-layer Navier–Stokes solutions are obtained for an incompressible laminar flow over a hemisphere–cylinder at 10°, 30° and 50° incidence to exhibit some three-dimensional separated flow characteristics. Some of the results are compared with a previous water-tunnel investigation for the same body geometry. Good agreement is found, even for some detailed features. Although the geometry is relatively simple, the separated flow surprisingly embraces a number of intricate structural characteristics unique to three-dimensional flows. Particularly noteworthy are the separation sequence at increasing incidence, tornado-like vortices, outward-spiralling vortices, limit cycles, coaxial counter-spiralling patterns and horseshoe vortex systems. Physical insights to these new features are offered.

Numerical Study on Supersonic Combustor with an Allotype Cavity

2014 ◽  
Vol 694 ◽  
pp. 187-192
Author(s):  
Jin Xiang Wu ◽  
Jian Sun ◽  
Xiang Gou ◽  
Lian Sheng Liu
Keyword(s):  
Alternative Model ◽  
Numerical Study ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Experimental Result ◽  
Navier Stokes ◽  
Cold Flow ◽  
Hypersonic Inlet ◽  
Good Agreement

The three-dimensional coupled explicit Reynolds Averaged Navier–Stokes (RANS) equations and the two equation shear-stress transport k-w (SST k-w) model has been employed to numerically simulate the cold flow field in a special-shaped cavity-based supersonic combustor. In a cross-section shaped rectangular, hypersonic inlet with airflow at Mach 2.0 chamber, shock structures and flow characteristics of a herringbone-shaped boss and a herringbone-shaped cavity models were discussed, respectively. The results indicate: Firstly, according to the similarities of bevel-cutting shock characteristics between the boss case and the cavity case, the boss structure can serve as an ideal alternative model for shear-layer. Secondly, the eddies within cavity are composed of herringbone-spanwise vortexes, columnar vortices in the front and main-spanwise vortexes in the rear, featuring tilting, twisting and stretching. Thirdly, the simulated bottom-flow of cavity is in good agreement with experimental result, while the reverse flow-entrainment resulting from herringbone geometry and pressure gradient. However, the herringbone-shaped cavity has a better performance in fuel-mixing.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Unsteady Flow at the Outlet of the High Specific Speed Centrifugal Compressor Impeller

1984 ◽  
Author(s):  
Fumikata Kano ◽  
Takafumi Shirakami
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Coal Gasification ◽  
Three Dimensional ◽  
Axial Direction ◽  
Navier Stokes ◽  
Meridional Plane ◽  
Mixed Flow ◽  
Navier Stokes Equation ◽  
Specific Speed

The unsteady flow at the outlet of the high specific speed mixed flow Impeller was studied. The specific speed is 500 (m3/min)1/2 · rpm · m−3/4. The flow is strongly influenced by the impeller blading. The other hand, the flow influences the performance of the stationary vanes downstream of the impeller. The flow path at the outlet of the mixed flow impeller is inclined to the axial direction and is curved in the meridional plane. The study was carried out to develop the 30 MW centrifugal compressor. This compressor is used in the field of the coal gasification, the geothermal power generation, etc. The distributions of flow velocity, pressure and temperature of three dimensional flow were measured using a high sensitive pressure transducer and a total temperature probe. The flow was surveyed across the entire passage at about ten axial locations including endwall boundary layer. A theoretical analysis was also carried out using the linearized Navier-Stokes equation.

Three-Dimensional Simulation of Turbulent Rectangular and Square Impinging Jet Flows

2004 ◽  
Author(s):  
Qingguang Chen ◽  
Zhong Xu ◽  
Yulin Wu ◽  
Yongjian Zhang
Keyword(s):  
Recirculation Zone ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Adverse Pressure Gradient ◽  
Impinging Jet ◽  
Boundary Layer Separation ◽  
Streamwise Velocity ◽  
Impinging Jets ◽  
Jet Flows ◽  
Dimensional Simulation

Flow characteristics of turbulent impinging jets issuing, respectively, from a rectangular and a square nozzles have been investigated numerically through the solution of three-dimensional Navier-Strokes equations in steady state. Two geometries with two nozzle-to-plate spacings of four and eight times of hydraulic diameters of the jet pipes, and two Reynolds numbers of 20000 and 30000 have been considered with fully developed inlet boundary conditions. An RNG based k–ε turbulence model and a deferred correction QUICK scheme in conjunction with the wall function method have been applied to the prediction of the flow fields within semi-confined spaces. A common feature revealed by the computational results is the presence of a toroidal recirculation zone around the jet. An adverse pressure gradient is found at the impingement surface downstream the stagnation point. Boundary layer separation will occur if the gradient is strong enough, and the separation manifests itself as a secondary recirculation zone at the surface. In addition, three-dimensional simulations reveal the existence of two and four pronounced streamwise velocity off-center peaks at the cross-planes near to the impingement plate, respectively, in the rectangular and square impinging jet flows. These peaks are found forming at the horizontal planes where the wall jets start forming accompanied by two or four pairs of counter-rotating vortex rings. It is believed that the formation of the off-center velocity peaks is due to the vorticity diffusion along the wall jet as the jet impinges on the target plate.

Enhancing the Centrifugal Compressor Performance Map Measurements Through a Developed One–Dimensional Calculation Tool to Analyse Local Flow Phenomena

2014 ◽  
Author(s):  
Matthias Hamann ◽  
Elias Chebli ◽  
Markus Müller ◽  
Alexander Krampitz
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Local Flow ◽  
One Dimensional ◽  
Casing Treatment ◽  
Surge Margin ◽  
Performance Map ◽  
Flow Phenomena ◽  
Compressor Performance

Centrifugal compressors for automotive turbochargers have large influence on the operation characteristic of combustion engines. Especially the improvement of the surge margin is one of the most important development targets. Thereby, a reliable detection of local flow phenomena within the compressor stage is necessary and a procedure to gain this information from standard measurement data is discussed in this paper. A one–dimensional calculation methodology for a single-stage centrifugal compressor with a vaneless diffuser and casing treatment is presented. The tool calculates the flow properties at the impeller inlet and exit as well as at diffuser exit, based on the measured inlet and outlet data and the geometry information of the compressor. The calculated flow characteristics are plotted within the measured compressor performance map to show local flow parameters. The unsteady recirculation flow within the casing treatment, the inflow angle and the total pressure losses are considered. The tool is validated on different compressor sizes. Thereby the compressor is equipped with static pressure measuring points at the impeller inlet and exit as well as at the diffuser exit. The calculated static pressure correlated well with the measured data with an accuracy of 2 % to 5 % on 95 % of the operating range. In this paper an experimental parameter study is executed in order to improve the surge margin. Thereby the geometry of the diffuser and the casing treatment is varied and the compressor performance is measured on a turbocharger test rig. The calculation of the flow angles and other flow characteristics within the diffuser enables one to find out whether surge is triggered through the diffuser or the impeller.

Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Yunfei Xing ◽  
Fengquan Zhong ◽  
Xinyu Zhang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Outer Wall ◽  
Centrifugal Effect

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k–ω turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

Numerical Flow Analysis in a Subsonic Vaned Radial Diffuser With Leading Edge Redesign

1999 ◽  
Vol 121 (1) ◽  
pp. 119-126 ◽  
Author(s):  
E. Casartelli ◽  
A. P. Saxer ◽  
G. Gyarmathy
Keyword(s):  
Static Pressure ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Leading Edge ◽  
Inverse Design ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Characteristic Lines ◽  
Design Software

The flow field in a subsonic vaned radial diffuser of a single-stage centrifugal compressor is numerically investigated using a three-dimensional Navier–Stokes solver (TASCflow) and a two-dimensional analysis and inverse-design software package (MISES). The vane geometry is modified in the leading edge area (two-dimensional blade shaping) using MISES, without changing the diffuser throughflow characteristics. An analysis of the two-dimensional and three-dimensional effects of two redesigns on the flow in each of the diffuser subcomponents is performed in terms of static pressure recovery, total pressure loss production, and secondary flow reduction. The computed characteristic lines are compared with measurements, which confirm the improvement obtained by the leading edge redesign in terms of increased pressure rise and operating range.

CFD analysis of the effect of nozzle stand-off distance on turbulent impinging jets

2013 ◽  
Vol 40 (7) ◽  
pp. 603-612 ◽  
Author(s):  
Mehrdad Shademan ◽  
Ram Balachandar ◽  
Ronald M. Barron
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Axial Direction ◽  
Reynolds Stress Model ◽  
Impinging Jets ◽  
Diameter Ratio ◽  
Wall Region ◽  
Nozzle Height ◽  
Jet Characteristics

Three-dimensional steady Reynolds Averaged Navier-Stokes simulations have been carried out to investigate the effect of the nozzle stand-off distance on the mean and turbulence characteristics of jets impinging vertically on flat surfaces. As part of the study, the performance of different turbulence models such as Realizable k–ε, k–ω SST, and Reynolds Stress Model (RSM) were evaluated. Based on comparisons with experimental data, RSM was chosen to further evaluate the characteristics of impinging jets. The Reynolds number based on the jet exit velocity and nozzle diameter is 100 000. Three different nozzle height-to-diameter ratios, representing different types of impinging jets, were simulated and compared with available experimental data. A strong dependency of the jet characteristics on the nozzle height-to-diameter ratio was observed. The simulations show that an increase in this ratio results in larger shear stress and more distributed pressure on the wall, more development of the flow in the axial direction and faster progress of the jet in the wall region. The current simulations present a robust step-by-step computational fluid dynamics approach to investigate the role of the nozzle height-to-diameter ratio on the impinging jet flow parameters.

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