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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

Coastal hydrodynamics beyond the surf zone of the south Baltic Sea

Ostrowski R., Stella M., Szmytkiewicz P., Kapiński J., Marcinkowski T.

Oceanologia

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2018

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No. 60 (3)

264--276

EN

The paper presents experimental and theoretical investigations of hydrodynamic processes in a coastal region located close to the seaward boundary of the surf zone. The analysis is based on field data collected near Lubiatowo (Poland) by measuring equipment operated simultaneously by the Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN) and the Maritime Institute in Gdańsk (IMG). The data consist of wind velocity and direction measured at the IBW PAN Coastal Research Station (CRS) in Lubiatowo, deep-water wave buoy records, current profiles and sea bottom sediment parameters. Mean flow velocities measured in the entire water column have almost the same direction as wind. Nearbed flow velocities induced by waves and currents, as well as bed shear stresses, are modelled theoretically to determine sediment motion regimes in the area. It appears that the nonlinear wave-current interaction generates bed shear stresses greater than those that would result from the superposition of the impacts of waves and currents separately. The paper discusses the possibility of occasional intensive sediment transport and the occurrence of distinct seabed changes at greater coastal water depths adjacent to the surf zone. It was found that this can happen under the joint influence of waves and wind-driven currents.

3

Wykorzystanie symulacji numerycznej do wyznaczania parametrów przepływu powietrza

Jabłoński M., Klemm K.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2016

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z. 63, nr 3

123--130

PL

W pracy przedstawiono procedurę wyznaczania podstawowych parametrów wpływających na profil prędkości wiatru tj. współczynnika szorstkości i prędkości tarciowej w oparciu o dane uzyskane z analiz symulacyjnych. W celu uchwycenia wpływu zabudowy na zmianę parametrów kształtujących profil prędkości wiatru przeprowadzono symulację numeryczną w oparciu o turbulencyjny model realizable k - ɛ. Analizę przeprowadzono dla prostego przypadku obiektu w kształcie walca o wymiarach ɸ =10 m i h=10 m zlokalizowanego w terenie otwartym o szorstkości podłoża zo=0,02 m. Korzystając z uzyskanych danych określono średnie wielkości prędkości u i dyssypacji energii ɛ, na trzech analizowanych wysokościach (2, 12, 16 m), w odległości 0, 21, 42 i 63 m od wlotu. W pierwszym wariancie współczynnik szorstkości i prędkość tarciową wyznaczono korzystając z profilu logarytmicznego prędkości wiatru, przyjmując przemieszczenie płaszczyzny zerowej zd zgodnie ze wzorem zaproponowanym w pracy [1]. W drugim wariancie wielkości ux i zo określono przyjmując założenie, że wystąpił pomijalnie mały efekt turbulencji termicznej QH = 4,7 W/m2. Główną bazą rozważań były równania wynikające z podobieństwa Monina Obukhova i bezwymiarowej funkcji ɸ (e) ی. Wielkości uzyskane w ramach wariantu pierwszego są możliwe do zaakceptowania. Natomiast wyniki otrzymane w wariancie drugim w odległości do 40m od wlotu wielokrotnie przewyższają poziom realny.

EN

The paper presents the procedure of determining the basic parameters affecting the wind speed profile, i.e. roughness coefficient and friction velocity based on numerical simulation. In order to show the impact of development on changes in parameters influencing wind speed profile numerical simulation has been carried out based on realizable K-ɛ model. The analysis was conducted for the simple case of cylindrical object with dimensions ɸ=10 m and h=10 m located in the open area with the roughness coefficient zo=0,02m. Based on obtained numerical results the average values of wind speed and energy dissipation were determined at three heights (2, 12, 16 m) in a distance of 0, 21, 42 and 63 m from the inlet. In a first variant roughness coefficient and friction velocity were determined using the logarithmic wind speed profile, assuming zero plane displacement in accordance with [1]. In the second variant, the size of ux and zo was determined on the assumption that there was a negligible effect of thermal turbulence QH = 4,7W/m2. The consideration were based on equation resulting from Monin Obukhov similarity and dimensionless function ɸ (e) ی. Results obtained in the first variant are acceptable. In contrast, the results obtained in the second variant, at the distance of 40m from the inlet are several times higher than realistic level.

4

Sediment transport beyond the surf zone under waves and currents of the non-tidal sea: Lubiatowo (Poland) case study

Ostrowski R., Stella M.

Archives of Hydro-Engineering and Environmental Mechanics

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2016

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Vol. 63, nr 1

63--77

EN

The paper deals with the sandy coastal zone at Lubiatowo in Poland (the south Baltic Sea). The study comprises experimental and theoretical investigations of hydrodynamic and lithodynamic processes in the coastal region located close to the seaward boundary of the surf zone and beyond the surf zone. The analysis is based on field data collected at the IBW PAN Coastal Research Station in Lubiatowo. The data consist of wind velocity reconstructed from the long-term wave climate, deep-water wave buoy records and sea bottom soil parameters. Nearbed flow velocities induced by waves and currents, as well as bed shear stresses are theoretically modelled for various conditions to determine sediment motion regimes in the considered area. The paper discusses the possibility of occasional intensive sediment transport and the occurrence of distinct sea bed changes at bigger water depths.

5

On Uncertainties in Determination of Sediment Transport Rates in Coastal Regions

Ostrowski R.

Archives of Hydro-Engineering and Environmental Mechanics

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2016

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Vol. 63, nr 4

265--280

EN

The paper deals with research uncertainties, difficulties, inaccuracies and unreliabilities related to the modelling of physical phenomena involving coastal lithodynamics. The considerations are focused on processes of wave transformation, wave-driven currents and sediment transport itself. It is shown that possible inaccuracies at individual stages of the modelling of coastal hydrodynamics can lead to serious uncertainties with respect to the ultimate modelling output, namely bed shear stresses and sediment transport rates. These inaccuracies result mostly from arbitrarily assumed parameters and constants. Other modelling biases discussed in the paper comprise simplifications and approximations with respect to sediment resources and size-graded properties, randomness of hydrodynamic impacts, bottom roughness and land-borne factors involved in coastal lithodynamics.

6

Effects of a fully submerged boulder within a boulder array on the mean and turbulent flow fields: Implications to bedload transport

Papanicolaou A., Kramer C., Tsakiris A., Stoesser T., Bomminayuni S., Chen Z.

Acta Geophysica

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2012

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Vol. 60, no. 6

1502-1546

EN

The objective of this coupled experimental and numerical study is to provide insight into the mean and turbulent flow fields within an array of fully submerged, isolated, immobile boulders. Our study showed that the velocity defect law performed well for describing the mean flow around the boulder within the array. A prerequisite, however, was to accurately estimate the spatial variability of u* around the boulder, which was achieved via the boundary characteristics method. The u* exhibited considerable spatial variability within the array and form roughness was shown to be up to 2 times larger than the skin roughness in the boulder near-wake region. Because the boulders bear a significant amount of the flow shear, the available bed shear stress for entrainment of the mobile sediment, τols, near the boulders was roughly 50% lower than the ambient τols. The τols variability induced by the boulders could lead to a threefold overestimation of the sediment transport rate.