The Suppression of Flow Separation by Sequential Wall Jets

1976 ◽  
Vol 98 (3) ◽  
pp. 447-452
Author(s):  
P. North
Keyword(s):  
Boundary Layer ◽  
Fluid Flow ◽  
Kinetic Energy ◽  
Energy Flux ◽  
Close Agreement ◽  
Total Kinetic Energy ◽  
Wall Jet ◽  
Wall Jets ◽  
Single Jet ◽  
Flow Devices

The performance of many fluid flow devices is limited by the separation of the turbulent boundary layer. This separation may be suppressed or delayed by use of wall jets, raising questions of jet location and strength. A numerical analysis of a single wall jet gave results in close agreement with experiment. The same analysis of a single wall jet gave results in close agreement with experiment. The same calculation procedure indicated that two sequential wall jets, with the same total kinetic energy flux as the single jet, would suppress separation under conditions where the single jet would not. The best two-jet arrangement would be achieved with 63 percent of the total kinetic energy flux in the first jet. It is possible that three-jet arrangements could provide some further improvement.

CLUES FOR THE COMPOSITION OF RELATIVISTIC MICROQUASAR JETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1947-1952 ◽  
Author(s):  
SEBASTIAN HEINZ
Keyword(s):  
Kinetic Energy ◽  
Energy Flux ◽  
Significant Contribution ◽  
Total Kinetic Energy ◽  
Singular Case ◽  
Relativistic Jets ◽  
Ss 433 ◽  
Jet Power ◽  
Entire Ensemble

We discuss the evidence for proton loading in relativistic jets from microquasars in light of recent constraints on the jet power. We argue that, both in the case of the Cygnus X-1 jet and the entire ensemble of Galactic microquasars, the evidence points towards a significant contribution to the total kinetic energy flux from cold protons. However, as with all other methods of constraining jet composition (except for the singular case of SS 433), a number of alternative, though maybe less plausible, explanations exist. In light of this continued elusiveness of a single slam-dunk argument for proton loading, the best we can hope for is a continuing accumulation of bits of evidence such as these which will, on the whole, form a preponderance of evidence against pure pair jets.

Heat Transfer to Plane Turbulent Wall Jets

1963 ◽  
Vol 85 (3) ◽  
pp. 209-213 ◽  
Author(s):  
G. E. Myers ◽  
J. J. Schauer ◽  
R. H. Eustis
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Temperature Distribution ◽  
Wall Jet ◽  
Analytical Prediction ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Wall Jets ◽  
Turbulent Wall Jets ◽  
Turbulent Wall

The heat-transfer characteristics of two-dimensional, incompressible, turbulent wall jets are discussed. An analytical prediction is made for the local Stanton number and data are presented for a step wall temperature distribution. The method for extending these data to arbitrary heating conditions is shown. Temperature surveys in the wall jet boundary layer are also presented.

The Departure from Equilibrium of Turbulent Boundary Layers

1968 ◽  
Vol 19 (1) ◽  
pp. 1-19 ◽  
Author(s):  
H. McDonald
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Kinetic Energy ◽  
Stress Distribution ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Two Dimensional ◽  
Pressure Distributions ◽  
Momentum Integral ◽  
State Examination

SummaryRecently two authors, Nash and Goldberg, have suggested, intuitively, that the rate at which the shear stress distribution in an incompressible, two-dimensional, turbulent boundary layer would return to its equilibrium value is directly proportional to the extent of the departure from the equilibrium state. Examination of the behaviour of the integral properties of the boundary layer supports this hypothesis. In the present paper a relationship similar to the suggestion of Nash and Goldberg is derived from the local balance of the kinetic energy of the turbulence. Coupling this simple derived relationship to the boundary layer momentum and moment-of-momentum integral equations results in quite accurate predictions of the behaviour of non-equilibrium turbulent boundary layers in arbitrary adverse (given) pressure distributions.

scholarly journals Spatiotemporal Dynamics of the Kinetic Energy in the Atmospheric Boundary Layer from Minisodar Measurements

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 421
Author(s):  
Alexander Potekaev ◽  
Liudmila Shamanaeva ◽  
Valentina Kulagina
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Time Of Day ◽  
Linear Increase ◽  
Spatiotemporal Dynamics ◽  
Intermediate Layers ◽  
Subsequent Decrease ◽  
Stable Atmospheric Boundary Layer

Spatiotemporal dynamics of the atmospheric kinetic energy and its components caused by the ordered and turbulent motions of air masses are estimated from minisodar measurements of three velocity vector components and their variances within the lowest 5–200 m layer of the atmosphere, with a particular emphasis on the turbulent kinetic energy. The layered structure of the total atmospheric kinetic energy has been established. From the diurnal hourly dynamics of the altitude profiles of the turbulent kinetic energy (TKE) retrieved from minisodar data, four layers are established by the character of the altitude TKE dependence, namely, the near-ground layer, the surface layer, the layer with a linear TKE increase, and the transitive layer above. In the first layer, the most significant changes of the TKE were observed in the evening hours. In the second layer, no significant changes in the TKE values were observed. A linear increase in the TKE values with altitude was observed in the third layer. In the fourth layer, the TKE slightly increased with altitude and exhibited variations during the entire observation period. The altitudes of the upper boundaries of these layers depended on the time of day. The MKE values were much less than the corresponding TKE values, they did not exceed 50 m2/s2. From two to four MKE layers were distinguished based on the character of its altitude dependence. The two-layer structures were observed in the evening and at night (under conditions of the stable atmospheric boundary layer). In the morning and daytime, the four-layer MKE structures with intermediate layers of linear increase and subsequent decrease in the MKE values were observed. Our estimates demonstrated that the TKE contribution to the total atmospheric kinetic energy considerably (by a factor of 2.5–3) exceeded the corresponding MKE contribution.

scholarly journals Port-Hamiltonian modeling of ideal fluid flow: Part I. Foundations and kinetic energy

2021 ◽  
Vol 164 ◽  
pp. 104201 ◽  
Author(s):  
Ramy Rashad ◽  
Federico Califano ◽  
Frederic P. Schuller ◽  
Stefano Stramigioli
Keyword(s):  
Fluid Flow ◽  
Kinetic Energy ◽  
Ideal Fluid ◽  
Ideal Fluid Flow ◽  
Flow Part

Analysis of an Airfoil Using a Transition and Turbulence Model

2016 ◽  
Vol 819 ◽  
pp. 356-360
Author(s):  
Mazharul Islam ◽  
Jiří Fürst ◽  
David Wood ◽  
Farid Nasir Ani
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Turbulence Model ◽  
Original Version ◽  
Transitional Region ◽  
Cfd Analysis ◽  
Computational Fluid Dynamics Cfd

In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-kL- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-kL-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

Heat Transfer Committee and Turbomachinery Committee Best Paper of 1996 Award: The Path to Predicting Bypass Transition

1997 ◽  
Vol 119 (3) ◽  
pp. 405-411 ◽  
Author(s):  
R. E. Mayle ◽  
A. Schulz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Energy Equation ◽  
Free Stream ◽  
Bypass Transition ◽  
Turbulence Level ◽  
Free Stream Turbulence ◽  
Energy Profiles ◽  
Computer Codes ◽  
Good Agreement

A theory is presented for calculating the fluctuations in a laminar boundary layer when the free stream is turbulent. The kinetic energy equation for these fluctuations is derived and a new mechanism is revealed for their production. A methodology is presented for solving the equation using standard boundary layer computer codes. Solutions of the equation show that the fluctuations grow at first almost linearly with distance and then more slowly as viscous dissipation becomes important. Comparisons of calculated growth rates and kinetic energy profiles with data show good agreement. In addition, a hypothesis is advanced for the effective forcing frequency and free-stream turbulence level that produce these fluctuations. Finally, a method to calculate the onset of transition is examined and the results compared to data.

The Boundary Layer Inside a Conical Surface Due to a Swirling Flow With Throughflow

1976 ◽  
Vol 43 (4) ◽  
pp. 564-566 ◽  
Author(s):  
J. M. Fabian ◽  
G. C. Oates
Keyword(s):  
Boundary Layer ◽  
Entire Range ◽  
Close Agreement ◽  
Swirling Flow ◽  
Approximate Solutions ◽  
Conical Surface

The problem of describing the boundary layer existing inside a conical surface due to the presence of a swirling flow passing through the cone is considered. Approximate solutions based upon the Karman-Polhausen method are obtained for both the laminar and the turbulent cases. The results obtained are in close agreement with known solutions previously obtained in the limits of swirl with no throughflow and throughflow with no swirl. The present results appear to be valid over the entire range of swirl to throughflow ratios.

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