Downstream evolution of junction flow three-component velocity fluctuations through the lens of the diagnostic plot
TL;DR: In this paper, the authors used the extended diagnostic plot to evaluate the departure of turbulent wing-body junction flow wakes from the boundary layer boundary layers and found that with downstream development, boundary layer eventually recovers to the base zero-pressure gradient "equilibrium", and this recovery process emanates from the near wall region.
About: This article is published in International Journal of Heat and Fluid Flow.The article was published on 2020-10-01. It has received 3 citations till now. The article focuses on the topics: Boundary layer & Secondary flow.
Citations
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TL;DR: In this article, the flow characteristics and noise generation at the finite wing-wall junction were investigated and acoustic measurements were taken in the aco-clockwise direction of the junction.
Abstract: This paper is concerned with the flow characteristics and noise generation at the finite wing–wall junction. To characterize junction flow noise, acoustic measurements were taken in the aco...
1 citations
25 Feb 2021
TL;DR: The diagnostic plot was introduced in 2010 (Eur. J. Mech. B/Fluids 29: 403-406) but was used already in 2008 during a large measurement campaign as a litmus test to determine if tripped zero pressure gradient turbulent boundary layers fulfilled basic criteria of being canonical.
Abstract: The diagnostic plot was introduced in 2010 (Eur. J. Mech. B/Fluids 29: 403–406) but was used already in 2008 during a large measurement campaign as a litmus test to determine if tripped zero-pressure gradient turbulent boundary layers fulfilled basic criteria of being canonical. It used the rms-level of streamwise velocity (\(u_\mathrm {rms}\)) in the outer part of the boundary layer, a region where \(u_\mathrm {rms}\) can give clear indications if insufficient or too tough tripping has been used. In standard plots one needs both the friction velocity and measurement of the full velocity and turbulence profiles. By instead plotting \(u_\mathrm {rms}/U_\infty \) as a function of \(U/U_\infty \), it was found that this gives rise to a well-defined distribution that could be used as a canonical measure. It was later discovered that it is possible to extend the description to the near wall region. It has also been extended to boundary layers over rough surfaces and with pressure gradients, and some further uses. This paper aims to be both a review of the development of the method during the last 10+ years and a tutorial for those who want to employ it in their research and maybe also find new uses of the methodology.
TL;DR: In this article , the mean pressure field in the junction region around wall-mounted wings with NACA 0012 and NACA 6412 wing section profiles was studied and three-dimensional RANS simulations for both wing profiles using five turbulence models were also presented.
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19 Dec 1975
TL;DR: In this paper, the authors present a method to find the optimal set of words for a given sentence in a sentence using the Bibliogr. Index Reference Record created on 2004-09-07, modified on 2016-08-08
Abstract: Note: Bibliogr. : p. 413-424. Index Reference Record created on 2004-09-07, modified on 2016-08-08
3,758 citations
TL;DR: In this paper, the velocity distribution and reattachment length of a single backward-facing step mounted in a two-dimensional channel were measured using laser-Doppler measurements.
Abstract: Laser-Doppler measurements of velocity distribution and reattachment length are reported downstream of a single backward-facing step mounted in a two-dimensional channel. Results are presented for laminar, transitional and turbulent flow of air in a Reynolds-number range of 70 < Re < 8000. The experimental results show that the various flow regimes are characterized by typical variations of the separation length with Reynolds number. The reported laser-Doppler measurements do not only yield the expected primary zone of recirculating flow attached to the backward-facing step but also show additional regions of flow separation downstream of the step and on both sides of the channel test section. These additional separation regions have not been previously reported in the literature.Although the high aspect ratio of the test section (1:36) ensured that the oncoming flow was fully developed and two-dimensional, the experiments showed that the flow downstream of the step only remained two-dimensional at low and high Reynolds numbers.The present study also included numerical predictions of backward-facing step flow. The two-dimensional steady differential equations for conservation of mass and momentum were solved. Results are reported and are compared with experiments for those Reynolds numbers for which the flow maintained its two-dimensionality in the experiments. Under these circumstances, good agreement between experimental and numerical results is obtained.
1,637 citations
TL;DR: In this paper, a simulation of the Navier-Stokes equations of a backward-facing step flow was performed at a Reynolds number of 5100 based on the step height h and inlet free-stream velocity.
Abstract: Turbulent flow over a backward-facing step is studied by direct numerical solution of the Navier–Stokes equations. The simulation was conducted at a Reynolds number of 5100 based on the step height h and inlet free-stream velocity, and an expansion ratio of 1.20. Temporal behaviour of spanwise-averaged pressure fluctuation contours and reattachment length show evidence of an approximate periodic behaviour of the free shear layer with a Strouhal number of 0.06. The instantaneous velocity fields indicate that the reattachment location varies in the spanwise direction, and oscillates about a mean value of 6.28h. Statistical results show excellent agreement with experimental data by Jovic & Driver (1994). Of interest are two observations not previously reported for the backward-facing step flow: (a) at the relatively low Reynolds number considered, large negative skin friction is seen in the recirculation region; the peak |Cf| is about 2.5 times the value measured in experiments at high Reynolds numbers; (b) the velocity profiles in the recovery region fall below the universal log-law. The deviation of the velocity profile from the log-law indicates that the turbulent boundary layer is not fully recovered at 20 step heights behind the separation.The budgets of all Reynolds stress components have been computed. The turbulent kinetic energy budget in the recirculation region is similar to that of a turbulent mixing layer. The turbulent transport term makes a significant contribution to the budget and the peak dissipation is about 60% of the peak production. The velocity–pressure gradient correlation and viscous diffusion are negligible in the shear layer, but both are significant in the near-wall region. This trend is seen throughout the recirculation and reattachment region. In the recovery region, the budgets show that effects of the free shear layer are still present.
1,076 citations
TL;DR: In this article, the Reynolds stresses and the dissipation rate of the turbulence kinetic energy are computed using direct simulation data of a turbulent channel flow using a closed-loop model, where the budget data reveal that all the terms in the budget become important close to the wall.
Abstract: The budgets for the Reynolds stresses and for the dissipation rate of the turbulence kinetic energy are computed using direct simulation data of a turbulent channel flow. The budget data reveal that all the terms in the budget become important close to the wall. For inhomogeneous pressure boundary conditions, the pressure-strain term is split into a return term, a rapid term, and a Stokes term. The Stokes term is important close to the wall. The rapid and return terms play different roles depending on the component of the term. A split of the velocity pressure-gradient term into a redistributive term and a diffusion term is proposed, which should be simpler to model. The budget data is used to test existing closure models for the pressure-strain term, the dissipation rate, and the transport rate. In general, further work is needed to improve the models.
788 citations
TL;DR: In this paper, it is shown that in sufficiently strong favorable and adverse pressure gradients the inner-law velocity distribution breaks down completely, and it is suggested that this breakdown is associated with reversion to laminar flow.
Abstract: Preston's method of measuring skin friction in the turbulent boundary layer makes use of a circular Pitot tube resting on the wall. On the assumption of a velocity distribution in the wall region common to boundary layer and pipe flows the calibration curve for the Pitot tube can be obtained in fully developed pipe flow. Earlier experiments suggested that Preston's original calibration was in error, and a revised calibration curve has been obtained and is presented here.From experiments in strong favourable and adverse pressure gradients, limits are assigned to the pressure-gradient conditions within which the calibration can be used with prescribed accuracy. It is shown that in sufficiently strong favourable gradients the ‘inner-law’ velocity distribution breaks down completely, and it is suggested that this breakdown is associated with reversion to laminar flow.As an incidental result, values have been obtained for the constants occurring in the logarithmic expression for the inner-law velocity distribution.
730 citations