scholarly journals Study on the Law of Pseudo-Cavitation on Superhydrophobic Surface in Turbulent Flow Field of Backward-Facing Step

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 200
Author(s):  
Xuecheng Lv ◽  
Wei-Tao Wu ◽  
Jizu Lv ◽  
Ke Mao ◽  
Linsong Gao ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Superhydrophobic Surface ◽  
Large Bubble ◽  
Backward Facing Step ◽  
Bubble Generation ◽  
Turbulent Flow Field ◽  
Flow Drag

Superhydrophobic surface is regarded as important topic in the field of thermal fluids today due to its unique features on flow drag reduction and heat transfer enhancement. In this study, the pseudo-cavitation phenomenon on the superhydrophobic surface in the backward-facing step turbulent flow field is observed through experiments. The underlying reason for this phenomenon is studied with experimental observation and analysis, and the time variant mechanisms of this phenomenon with various Reynolds number is summarized. The research results indicate that the superhydrophobic surface and the backward-facing step provide the material basis and dynamic condition for the generation of pseudo-cavitation. The pseudo-cavitation induces a large bubble on the superhydrophobic surface below the backward-facing step. The size, position, shape, oscillation amplitude, detachment, and splitting of the large bubble show regularity with the changes of Reynolds number. Meanwhile, the bubble growth, oscillation, detachment, split, and regeneration over time also show regularity. The study of bubble generation and development laws can be used to better control the perturbation of the flow field. Importantly, the present study has meaning in better understanding the flow mechanisms and gas coverage of superhydrophobic surface under condition of backward-facing step, paving the way for studying the flow drag reduction effect of superhydrophobic surface.

Turbulence Measurements in the Corner Wall Jet

2014 ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Wall Jet ◽  
Hot Wire ◽  
Turbulence Measurements ◽  
Vertical Growth ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one half of the surface has been rotated counter-clockwise by 90 degrees. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry. The results indicate that the ratio of lateral to vertical growth in the corner wall jet is approximately half of that in a standard turbulent three-dimensional wall jet.

Heterogeneous Drag Reduction Concepts and Consequences

1998 ◽  
Vol 120 (4) ◽  
pp. 818-823 ◽  
Author(s):  
Klaus W. Hoyer ◽  
Albert Gyr
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Polymer Solution ◽  
Large Scale ◽  
Scale Interaction ◽  
Polymer Molecules ◽  
Pipe Flows ◽  
Heterogeneous Drag Reduction ◽  
Turbulent Flow Field

This paper deals with the nature of the heterogeneous drag reduction which occurs in turbulent pipe flows when a concentrated polymer solution is injected into the pipe center. According to earlier concepts, the achieved drag reduction is due to a direct, large-scale interaction of the viscoelastic polymer thread with the turbulent flow field. The authors prove that the heterogeneous drag reduction originates exclusively from agglomerates of dissolved polymer molecules present in the flow.

Turbulence Measurements in a Corner Wall Jet1

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Numerical Code ◽  
Wall Jet ◽  
Hot Wire ◽  
Practical Applications ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one-half of the surface has been rotated counterclockwise by 90 deg. The corner wall jet is selected for study as the geometry occurs in practical applications and is an ideal benchmark case for numerical code validation. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry from x/D = 0 to 40. The results indicate that the ratio of lateral-to-vertical growth in the corner wall jet is approximately half that in a standard turbulent three-dimensional wall jet. The results indicate that this behavior is not simply tied to a slower development of the corner wall jet.

scholarly journals Noise Reduction Effect of Superhydrophobic Surfaces with Streamwise Strip of Channel Flow

2021 ◽  
Vol 11 (9) ◽  
pp. 3869
Author(s):  
Chen Niu ◽  
Yongwei Liu ◽  
Dejiang Shang ◽  
Chao Zhang
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Noise Reduction ◽  
Channel Flow ◽  
Superhydrophobic Surface ◽  
Sound Field ◽  
Flow Noise ◽  
Slip Boundary ◽  
Eddy Simulation ◽  
Reduction Effect

Superhydrophobic surface is a promising technology, but the effect of superhydrophobic surface on flow noise is still unclear. Therefore, we used alternating free-slip and no-slip boundary conditions to study the flow noise of superhydrophobic channel flows with streamwise strips. The numerical calculations of the flow and the sound field have been carried out by the methods of large eddy simulation (LES) and Lighthill analogy, respectively. Under a constant pressure gradient (CPG) condition, the average Reynolds number and the friction Reynolds number are approximately set to 4200 and 180, respectively. The influence on noise of different gas fractions (GF) and strip number in a spanwise period on channel flow have been studied. Our results show that the superhydrophobic surface has noise reduction effect in some cases. Under CPG conditions, the increase in GF increases the bulk velocity and weakens the noise reduction effect. Otherwise, the increase in strip number enhances the lateral energy exchange of the superhydrophobic surface, and results in more transverse vortices and attenuates the noise reduction effect. In our results, the best noise reduction effect is obtained as 10.7 dB under the scenario of the strip number is 4 and GF is 0.5. The best drag reduction effect is 32%, and the result is obtained under the scenario of GF is 0.8 and strip number is 1. In summary, the choice of GF and the number of strips is comprehensively considered to guarantee the performance of drag reduction and noise reduction in this work.

Numerical simulations and analysis of the turbulent flow field in a practical gas turbine engine combustor

2021 ◽  
pp. 095765092110632
Author(s):  
Veeraraghava R Hasti ◽  
Prithwish Kundu ◽  
Sibendu Som ◽  
Jay P Gore
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Gas Turbine ◽  
Adaptive Mesh Refinement ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Turbulent Structures ◽  
Cut Cell ◽  
Turbulent Flow Field

The turbulent flow field in a practical gas turbine combustor is very complex because of the interactions between various flows resulting from components like multiple types of swirlers, dilution holes, and liner effusion cooling holes. Numerical simulations of flows in such complex combustor configurations are challenging. The challenges result from (a) the complexities of the interfaces between multiple three-dimensional shear layers, (b) the need for proper treatment of a large number of tiny effusion holes with multiple angles, and (c) the requirements for fast turnaround times in support of engineering design optimization. Both the Reynolds averaged Navier–Stokes simulation (RANS) and the large eddy simulation (LES) for the practical combustor geometry are considered. An autonomous meshing using the cut-cell Cartesian method and adaptive mesh refinement (AMR) is demonstrated for the first time to simulate the flow in a practical combustor geometry. The numerical studies include a set of computations of flows under a prescribed pressure drop across the passage of interest and another set of computations with all passages open with a specified total flow rate at the plenum inlet and the pressure at the exit. For both sets, the results of the RANS and the LES flow computations agree with each other and with the corresponding measurements. The results from the high-resolution LES simulations are utilized to gain fundamental insights into the complex turbulent flow field by examining the profiles of the velocity, the vorticity, and the turbulent kinetic energy. The dynamics of the turbulent structures are well captured in the results of the LES simulations.

Turbulent flow-field effects in a hybrid CFD-CRN model for the prediction of NO and CO emissions in aero-engine combustors

Fuel ◽  
2018 ◽  
Vol 215 ◽  
pp. 853-864 ◽  
Author(s):  
A. Innocenti ◽  
A. Andreini ◽  
D. Bertini ◽  
B. Facchini ◽  
M. Motta
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Field Effects ◽  
Aero Engine ◽  
Turbulent Flow Field
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