Wall-Model for Turbulent Flows Under an Adverse Pressure Gradient - Asymmetric Diffuser

2021 ◽  
Author(s):  
Ionut Stelian Grecu ◽  
Georgiana Dunca ◽  
Diana Maria Bucur ◽  
Michel J. Cervantes
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Adverse Pressure Gradient ◽  
Wall Model

Structural Parameters and Prediction of Adverse Pressure Gradient Turbulent Flows: An Improved k-ε Model

1995 ◽  
Vol 117 (3) ◽  
pp. 424-432 ◽  
Author(s):  
G. Chukkapalli ◽  
O¨. F. Turan
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Structural Parameters ◽  
Adverse Pressure Gradient ◽  
Reynolds Stress Model ◽  
Model Representation ◽  
Stress Model ◽  
Kinetic Diffusion

A modified k-ε model is proposed to predict complex, adverse pressure gradient, turbulent diffuser flows. The need for an eddy viscosity is eliminated by using three structural parameters. A fuller treatment of the rate of kinetic diffusion terms is incorporated with a Reynolds stress model representation. A thorough evaluation is given of the three structural parameters in three decreasing and one increasing adverse pressure gradient diffuser flows leading to a three-layer representation. The results indicate the need for better modeling of the ε-equation.

The Structure of Forward Facing Step Flows in Adverse Pressure Gradient

2014 ◽  
Author(s):  
Weijie Shao ◽  
Martin Agelin-Chaab
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Decomposition Analysis ◽  
Adverse Pressure Gradient ◽  
Quality Data ◽  
Reattachment Length ◽  
Mean Flow ◽  
Particle Image Velocimetry Technique ◽  
The Mean ◽  
Forward Facing Step

This paper reports an investigation of the effects of adverse pressure gradient on turbulent flows over forward facing step. Three adverse pressure gradients were created for this study using diverging channels. A particle image velocimetry technique was used to conduct measurements in the streamwise-wall-normal (x-y) planes at the mid-plane of test section at several locations downstream to 68 step heights. A Reynolds number of Reh = 4800 and δ/h = 4.7 were employed, where h is the mean step height and δ is the approach boundary layer thickness. The results include the mean flow and turbulence quantities as well as proper orthogonal decomposition analysis. The mean reattachment length obtained indicates that the adverse pressure gradient created in this study does not have significant effects on the reattachment length. The triple velocity correlations imply that there is negative transport of turbulence kinetic energy close to the wall and positive transport away from the wall. In addition to the physical insight, the high quality data reported are useful for assessing the ability of turbulence models to reproduce the behaviour of complex flows.

scholarly journals A predictive inner–outer model for streamwise turbulence statistics in wall-bounded flows

2011 ◽  
Vol 681 ◽  
pp. 537-566 ◽  
Author(s):  
ROMAIN MATHIS ◽  
NICHOLAS HUTCHINS ◽  
IVAN MARUSIC
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Large Scale ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Gradient Flows ◽  
Streamwise Pressure Gradient ◽  
Logarithmic Region ◽  
Inner Region

A model is proposed with which the statistics of the fluctuating streamwise velocity in the inner region of wall-bounded turbulent flows are predicted from a measured large-scale velocity signature from an outer position in the logarithmic region of the flow. Results, including spectra and all moments up to sixth order, are shown and compared to experimental data for zero-pressure-gradient flows over a large range of Reynolds numbers. The model uses universal time-series and constants that were empirically determined from zero-pressure-gradient boundary layer data. In order to test the applicability of these for other flows, the model is also applied to channel, pipe and adverse-pressure-gradient flows. The results support the concept of a universal inner region that is modified through a modulation and superposition of the large-scale outer motions, which are specific to the geometry or imposed streamwise pressure gradient acting on the flow.

PIV Study of Adverse and Favorable Pressure Gradient Turbulent Flows Over Transverse Ribs

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Adverse Pressure Gradient ◽  
Bottom Wall ◽  
Combined Effects ◽  
Mean Flow ◽  
Turbulent Statistics ◽  
Favorable Pressure Gradient ◽  
The Mean

This paper reports an experimental study of the combined effects of rib roughness and pressure gradient on turbulent flows produced in asymmetric converging and diverging channels. Transverse square ribs with pitch-to-height ratio of 4 were attached to the bottom wall of the channel to produce the rib roughness. A particle image velocimetry technique was used to conduct measurements at several streamwise-transverse planes located upstream, within, and downstream of the converging and diverging sections of the channel. From these measurements, the mean velocities and turbulent statistics at the top plane of the ribs and across the channel were obtained. The data revealed non-negligible wall-normal motion and interaction between the cavities and overlying boundary layers. The different drag characteristics of the rough bottom wall and the smooth top wall produced asymmetric distributions of mean velocity and turbulent statistics across the channel. The asymmetry of these profiles is most extreme in the presence of adverse pressure gradient. Because of the manner in which pressure gradient modifies the mean flow and turbulence production, it was found that the streamwise turbulence intensity and Reynolds shear stress in the vicinity of the ribs are lower in the adverse pressure gradient than in the favorable pressure gradient channel. The results show also that the combined effects of rib roughness and adverse pressure gradient on the turbulent intensity statistics are significantly higher than when roughness and adverse pressure gradient are applied in isolation.

Structure of Turbulent Flows Over Forward Facing Steps With Adverse Pressure Gradient

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Hassan Iftekhar ◽  
Martin Agelin-Chaab
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Large Scale ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Step Height ◽  
Reattachment Length ◽  
Mean Velocity ◽  
The Mean

This paper reports an experimental study on the effects of adverse pressure gradient (APG) and Reynolds number on turbulent flows over a forward facing step (FFS) by employing three APGs and three Reynolds numbers. A particle image velocimetry (PIV) technique was used to conduct velocity measurements at several locations downstream, and the flow statistics up to 68 step heights are reported. The step height was maintained at 6 mm, and the Reynolds numbers based on the step height and freestream mean velocity were 1600, 3200, and 4800. The mean reattachment length increases with the increase in Reynolds number without the APG whereas the mean reattachment length remains constant for increasing APG. The proper orthogonal decomposition (POD) results confirmed that higher Reynolds numbers caused the large-scale structures to be more defined and organized close to the step surface.

scholarly journals The effects of minute vortex generator jet in a turbulent boundary layer with adverse pressure gradient

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110232
Author(s):  
Mohammad Javad Pour Razzaghi ◽  
Cheng Xu ◽  
Yue Liu ◽  
Yasin Masoumi
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Velocity Ratio ◽  
Vortex Formation ◽  
Vortex Generator ◽  
Adverse Pressure Gradient ◽  
Passive Flow Control ◽  
Vortex Generator Jet

Experimental and numerical analysis of active and passive flow control is an important topic of practical value in the study of turbulent flows. This paper numerically analyzed the effects of an air microjet on an adverse pressure gradient turbulent boundary layer over a flat plane. Experimental data were employed to verify the numerical modeling. Vortex formation and development were then studied by changing the microjet to inflow velocity ratio (VR) and microjet angles. According to the results, the best values of the angles [Formula: see text] and [Formula: see text] for various velocities were found to be 30° and from 60° to 90°, respectively. Moreover, at VRs = 1, 2, and 4, the [Formula: see text] values (the distance at which the complete vortex persisted in the flow) were 0.058, 0.078, and 0.18, respectively. Compared to VR = 1, the vortex strength for VRs = 2 and 4 grew by 3.5 and 6.8 times, respectively. When the microjet was added to the flow, the highest variation in the Reynolds stress along the x-direction from VR = 1–4 was 10%. The corresponding values along the y and z- directions were 15% and 2.7 times, respectively.

PIV Study of Turbulent Flow in Asymmetric Converging and Diverging Channels

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
M. K. Shah ◽  
M. F. Tachie
Keyword(s):  
Turbulent Flow ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Lower Boundary ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Mean Flow ◽  
The Mean ◽  
Converging And Diverging Channels

An experimental investigation of turbulent flow subjected to variable adverse and favorable pressure gradients in two-dimensional asymmetric channels is reported. The floors of the diverging and converging channels were flat while the roofs of the channels were curved. Adverse pressure gradient flows at Reh=27,050 and 12,450 and favorable pressure gradient flow at Reh=19,280 were studied. A particle image velocimetry was used to conduct detailed measurements at several planes upstream, within the variable section and within the downstream sections. The boundary layer parameters were obtained in the upper and lower boundary layers to study the effects of pressure gradients on the development of the mean flow on the floor and roof of the channels. The profiles of the mean velocities, turbulence intensities, Reynolds shear stress, mixing length, eddy viscosity, and turbulence production were also obtained to document the salient features of pressure gradient turbulent flows in asymmetric converging and diverging channels.

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