The identification of two distinct laminar to turbulent transition modes in pipe flows accelerated from rest

1989 ◽  
Vol 7 (4) ◽  
pp. 271-274 ◽  
Author(s):  
E. A. Moss
Keyword(s):  
Pipe Flows ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Transition Modes

scholarly journals Laminar-to-turbulent transition of pipe flows through puffs and slugs

2008 ◽  
Vol 614 ◽  
pp. 425-446 ◽  
Author(s):  
MINA NISHI ◽  
BÜLENT ÜNSAL ◽  
FRANZ DURST ◽  
GAUTAM BISWAS
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Axial Direction ◽  
Reynolds Numbers ◽  
Turbulent Pipe Flow ◽  
Test Facility ◽  
Pipe Flows ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Slug Flows

Laminar-to-turbulent transition of pipe flows occurs, for sufficiently high Reynolds numbers, in the form of slugs. These are initiated by disturbances in the entrance region of a pipe flow, and grow in length in the axial direction as they move downstream. Sequences of slugs merge at some distance from the pipe inlet to finally form the state of fully developed turbulent pipe flow. This formation process is generally known, but the randomness in time of naturally occurring slug formation does not permit detailed study of slug flows. For this reason, a special test facility was developed and built for detailed investigation of deterministically generated slugs in pipe flows. It is also employed to generate the puff flows at lower Reynolds numbers. The results reveal a high degree of reproducibility with which the triggering device is able to produce puffs. With increasing Reynolds number, ‘puff splitting’ is observed and the split puffs develop into slugs. Thereafter, the laminar-to-turbulent transition occurs in the same way as found for slug flows. The ring-type obstacle height, h, required to trigger fully developed laminar flows to form first slugs or puffs is determined to show its dependence on the Reynolds number, Re = DU/ν (where D is the pipe diameter, U is the mean velocity in the axial direction and ν is the kinematic viscosity of the fluid). When correctly normalized, h+ turns out to be independent of Reτ (where h+ = hUτ/ν, Reτ = DUτ/ν and $U_{\tau}\,{=}\,\sqrt{\tau_{w}/ \rho}$; τw is the wall shear stress and ρ is the density of the fluid).

Friction Factor for Transient Flow in Transverse Corrugated Pipes

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
C. O. Popiel ◽  
M. Kozak ◽  
J. Małecka ◽  
A. Michalak
Keyword(s):  
Friction Factor ◽  
Transient Flow ◽  
Minimum Diameter ◽  
Pressure Losses ◽  
Pipe Flows ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Friction Factors ◽  
Regular Roughness ◽  
Very High

Since the pressure losses in corrugated pipe flows are very high, their friction factor was investigated experimentally. Results of measurements of friction factor in laminar to turbulent transition zone of water flow in transverse corrugated pipes having regular roughness of approximately sinusoidal type are presented. The friction factors for four investigated commercially available pipes are increasing asymptotically to some maximum values with rising Reynolds number. Results were obtained for the corrugation depth to minimum diameter ratios, 0.103 ≤ e/d ≤ 0.148 and for the relative corrugation pitch, 0.462 ≥ P/d ≥ 0.270.

Laminar to turbulent transition in a finite length square duct subjected to inlet disturbance

2021 ◽  
Vol 33 (6) ◽  
pp. 065128
Author(s):  
Hamid Hassan Khan ◽  
Syed Fahad Anwer ◽  
Nadeem Hasan ◽  
Sanjeev Sanghi
Keyword(s):  
Finite Length ◽  
Square Duct ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition

Drag optimisation of a wing equipped with a morphing upper surface

2016 ◽  
Vol 120 (1225) ◽  
pp. 473-493 ◽  
Author(s):  
A. Koreanschi ◽  
O. Sugar-Gabor ◽  
R. M. Botez
Keyword(s):  
Genetic Algorithm ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Open Source ◽  
Experimental Testing ◽  
Shape Reconstruction ◽  
Laminar To Turbulent Transition ◽  
Wing Model ◽  
Turbulent Transition ◽  
Transition Delay

ABSTRACTThe drag coefficient and the laminar-to-turbulent transition for the aerofoil component of a wing model are optimised using an adaptive upper surface with two actuation points. The effects of the new shaped aerofoils on the global drag coefficient of the wing model are also studied. The aerofoil was optimised with an ‘in-house’ genetic algorithm program coupled with a cubic spline aerofoil shape reconstruction and XFoil 6.96 open-source aerodynamic solver. The wing model analysis was performed with the open-source solver XFLR5 and the 3D Panel Method was used for the aerodynamic calculation. The results of the aerofoil optimisation indicate improvements of both the drag coefficient and transition delay of 2% to 4%. These improvements in the aerofoil characteristics affect the global drag of the wing model, reducing it by up to 2%. The analyses were conducted for a single Reynolds number and speed over a range of angles of attack. The same cases will also be used in the experimental testing of the manufactured morphing wing model.

Sign in / Sign up

Export Citation Format

Share Document