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1

Application of the diagnostic plot in estimation of the skin friction in turbulent boundary layer under an adverse pressure gradient

Niegodajew P., Dróżdż A., Elsner W.

Archives of Mechanics

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2021

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Vol. 73, nr 2

201--215

EN

The paper concerns the problem of determining friction velocity in wallbounded flows affected by an adverse pressure gradient (APG). In the work of Niegodajew et al. [22] the corrected Clauser chart method (CCCM) for such flow conditions was proposed. This approach utilises the mean velocity profiles and turbulence intensity profiles to accurately estimate the friction velocity. In another work, Drózdz et al. [27] presented a modified version of the diagnostic-plot scaling (DPS) which allows for direct reconstruction of turbulence intensity profiles based on the local mean velocity profile, even when the flow is affected by a strong pressure gradient. This paper is aimed at verifying whether, when combining both of these methods (i.e. DPS and CCCM), the friction velocity can be accurately determined for APG flow conditions and one can possibly take advantage from both methods. The analysis revealed that the new approach is able to predict the friction velocity with uncertainty less than 5% for all the considered cases for the Clauser–Rotta parameter β < 17. Lastly, DPS-CCCM was also confronted with two empirical approaches (from available literature) allowing for estimation of the friction velocity under APG conditions. The performance of DPS-CCCM was found to be better than the ones of two other empirical approaches.

2

On streamwise structures in boundary layer under adverse pressure gradient on inclined plate

Uruba V., Prochazka P., Skala V.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2018

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Vol. 22, No 3

255--267

EN

The presented study is focused on experimental investigation of a boundary layer on a flat plate in an adverse pressure gradient. The flat plate is placed in a regular flow, the pressure gradient is generated by the plate inclination. The preceding studies deal with the structure of the wake behind the plate, the presented study concentrates on the flow structureclose to the suction surface of the plate. The dynamical behavior of the flow structures is studied in details with respect to the topology in the streamwise direction. In spite of the fact that thetime-mean flow field is close to 2D, more or less constant along the span, the instantaneous structures topology is fully 3D. Rather oblique structures are detected instead of those oriented in the streamwise direction. The patterns are travelling in the streamwise direction along the plate.

3

Amplitude modulated near-wall cycle in a turbulent boundary layer under an adverse pressure gradient

Dróżdż A., Elsner W.

Archives of Mechanics

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2013

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Vol. 65, nr 6

511--525

EN

This paper presents the effect of amplitude modulation of small-scale turbulence by large-scale structures in a turbulent boundary layer subjected to an adverse pressure gradient. The results have been compared with the literature data for high Reynolds number, zero-pressure gradient cases (Mathis et al. [1]). It was observed that for relatively low-Reynolds-number turbulent boundary layer (Reτ ≈ 1000) subjected to the adverse pressure gradient, apart from the inner peak of streamwise velocity fluctuations u, a second maximum located in the outer zone of turbulent boundary layer appears. It was found that the large-scale motions are much more energetic for adverse pressure gradients compared with the zero gradient case and the pressure gradient affects mostly the outer region of the flow. Using the method proposed by Mathis et al. [1], based on the correlation function and Hilbert transform, we obtained a clear evidence of a strong correlation between small inner-layer and large log-layer structures, which is similar to that observed for high Reynolds number zeropressure gradient cases. A simple model of modulation process occurring in adverse pressure gradient boundary layer has been proposed.

4

Application of VITA technique for detection of the organized structures present in a turbulent boundary layer under an adverse pressure gradient

Dróżdż A., Elsner W., Drobniak S.

Archives of Mechanics

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2011

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Vol. 63, nr 2

183-199

EN

The paper concerns experimental investigations of turbulent boundary layer (TBL), developing on a flat plate at Reynolds number based on momentum thickness= 3000 under an adverse pressure gradient (APG) corresponding to the case of pressure variation at axial compressor blading. In particular, the paper deals with the analysis of bursting phenomena and coherent structures activity in TBL with the use of VITA technique. The interpretation of coherent structures was based on the analysis of conditionally averaged traces of u and v velocity components recorded by X-wire probe in several boundary layer regions. The paper describes the modification introduced into the VITA method, which enables to distinguish four types of coherent structures. This modification relies on the detection of instantaneous positive or negative gradients of u and v velocity traces. It was found that bursting process under the influence of adverse pressure gradient is damped near the wall and this phenomenon is even more pronounced in the outer region of turbulent boundary layer. Furthermore, the paper gives the consistent proof, that vortices developing in TBL create the effect of bursting present in velocity signal.

5

The structure of turbulent boundary layer with adverse pressure gradient corresponding to turbomachinery condition

Materny M, Dróżdż A, Drobniak S, Elsner W

Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka

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2008

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nr 133

221--228

EN

The paper deals with the experimental analysis of turbulent boundary layer at the flat plate for large value of Reynolds number equal Reθ ≈ 3000. The adverse pressure gradient generated by curvature of the upper wall corresponded to the case of pressure variation in axial compressor. The fully developed turbulence structure was achieved by proper triggering of the boundary layer. The mean and turbulent flow – fields were investigated with the use of hot–wire technique.