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1
Content available Prediction of laminar-to-turbulent transition in a separated boundary layer subjected to an external acoustic forcing
Kubacki S., Rarata Z., Drózdz A., Gnatowska R., Sokolenko V., Elsner W.
Archives of Mechanics
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2023
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Vol. 75, nr 5
591--616
EN
The new Reynolds-averaged Navier–Stokes (RANS)-based method has been developed for taking into account, in an approximate manner, the effect of external acoustic forcing on laminar-to-turbulent transition in a separated boundary layer. Experimental studies [33] report an increase of the turbulent shear stress within the separated boundary layer under the influence of acoustic forcing. Enhancement of flow disturbances in a reversed flow region was also reported in our experiment. Experimental findings stimulated the development of a reduced-order aero-acoustic strategy. The effect of acoustic forcing was incorporated into the modelling framework of an algebraic intermittency model. The model component was tuned based on our experimental data and validated on reference experiments. The results show the feasibility of the proposed model to simulate flow over a flat plate and the NACA0018 profile.
2
Content available remote Prediction of secondary flow losses in an entrance duct to a low-pressure turbine
Jonak P., Borzęcki T., Kubacki S.
Archives of Mechanics
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2019
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Vol. 71, nr 1
65--90
EN
Secondary flow features and total pressure losses by means of the total pressure loss coefficient are discussed in an entrance duct, named a turbine central frame (TCF), to a four-stage low-pressure turbine (LPT) of aero-engine. The massaveraged total pressure losses are also analysed at outlets from selected components of the low-pressure turbine. The Reynolds-averaged Navier–Stokes (RANS) technique has been employed for prediction of mean flow characteristics. The numerical results are compared with experimental data obtained in Polonia Aero Lab in Zielonka (Poland). Good agreement is obtained between measured and predicted global flow characteristics and the pressure coefficient on a surface of an inlet guide vane. The high values of the loss coefficient are observed at endwalls, in cores of streamwiseoriented vortex structures near to the endwalls and in the wakes behind the vanes. It is found that the endwall losses contribute by far the most to the total losses at the outlets from the turbine central frame and first vane-row and they become lower at an outlet f rom the first blade-row and at outlets form consecutive vane- and blade-rows.
3
Content available remote Hybrid RANS/LES of plane jets impinging on a flat plate at small nozzle-plate distances
Kubacki S., Rokicki J., Dick E., Degroote J., Vierendeels J.
Archives of Mechanics
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2013
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Vol. 65, nr 2
143--166
EN
A k-ω based hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) model is tested for simulation of plane impinging jets at various nozzle-plate distances (H/B, where H is the distance and B is the slot's width) and various Reynolds numbers (based on the slot's width and the velocity in the symmetry plane). The studied combinations are H/B=2 for Re=10000, H/B=4 for Re=18000 and H/B=9.2 for Re=20000. The focus is on small distance of the nozzle exit to the plate. In LES mode, the hybrid RANS/LES model uses two definitions of the local grid size, one based on the maximum distance between the cell faces in the destruction term of the turbulent kinetic energy equation and one based on the cube root of the cell volume in the eddy-viscosity formula. This allows accounting for flow inhomogeneity on anisotropic grids. In RANS mode, the hybrid model turns into the newest version of the k-ω model by Wilcox.
4
Content available Kompleksowa automatyzacja i monitorowanie sieci SN kluczowym elementem poprawy niezawodności i ciągłości dostaw energii
Kubacki S., Świderski J., Tarasiuk M.
Acta Energetica
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2012
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nr 1
57-63
PL
Artykuł porusza zagadnienie kompleksowej automatyzacji i monitorowania sieci średniego napięcia (SN) jako kluczowego elementu koncepcji sieci inteligentnej (ang. Smart Grid). Omówiono stan istniejący w zakresie sterowania i monitorowania sieci SN oraz przedstawiono koncepcję rozwiązania dającego możliwość zdalnej, automatycznej rekonfiguracji sieci oraz zapewniającego pełną obserwowalność sieci z poziomu systemu dyspozytorskiego. Szczegółowo omówiono automatyzację przełączeń w sieci SN w celu wyizolowania uszkodzonego odcinka linii i zasilenia w energię elektryczną w chwili wystąpienia awarii możliwie największej liczby odbiorców. Przedstawiono również przykład działania takiej automatyki. W drugiej części artykułu zaprezentowano kluczową rolę funkcji szybkiej lokalizacji miejsca zwarcia oraz możliwości zdalnej rekonfiguracji sieci SN w celu poprawy niezawodności zasilania (poprawy wskaźników SAIDI, SAIFI). Pokazano również, jak wzrost liczby punktów wyposażonych w układy wykrywające przepływ prądów zwarciowych wraz z możliwością zdalnego sterowania łącznikami z systemu dyspozytorskiego w sieci SN może wpłynąć na zmniejszenie wskaźników SAIDI i SAIFI w poszczególnych oddziałach Energa -Operator SA.
EN
The paper presents the issue of comprehensive automation and monitoring of medium voltage (MV) grids as a key element of the Smart Grid concept. The existing condition of MV grid control and monitoring is discussed, and the concept of a solution which will provide the possibility of remote automatic grid reconfiguration and ensure full grid observability from the dispatching system level is introduced. Automation of MV grid switching is discussed in detail to isolate a faulty line section and supply electricity at the time of the failure to the largest possible number of recipients. An example of such automation controls’ operation is also presented. The paper’s second part presents the key role of the quick fault location function and the possibility of the MV grid’s remote reconfiguration for improving power supply reliability (SAIDI and SAIFI indices). It is also shown how an increase in the number of points fitted with faulted circuit indicators with the option of remote control of switches from the dispatch system in MV grids may affect reduction of SAIDI and SAIFI indices across ENERGA-OPERATOR SA. divisions.
5
Content available remote Hybrid RANS/LES computation of plane impinging jet flow
Kubacki S., Rokicki J., Dick E.
Archives of Mechanics
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2011
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Vol. 63, nr 2
117-117
EN
Flow characteristics are presented of simulation results of plane impinging jets at high nozzle-plate distances, with two k-? based hybrid RANS/LES (Reynolds Averaged Navier–Stokes/Large–Eddy Simulation) models and a k-? RANS model. The first hybrid RANS/LES model is obtained by substitution of the turbulent length scale by the local grid size in the destruction term of the turbulent kinetic energy equation and in the definition of the eddy-viscosity. The second hybrid model is obtained by a latency factor in the definition of the eddy-viscosity. The RANS model overpredicts the length of the jet core region, caused by too weak turbulent mixing in the shear layers of the jet. This results in erroneous near-wall shear stress along the impingement plate. The hybrid RANS/LES models overcome the deficiency of the RANS model. Further, the hybrid models represent the flow with much more detail. For instance, the Görtler vortices are well reproduced in the stagnation flow region by the hybrid RANS/LES models.
6
Dopuszczalność zmian umów w związku ze zmianą stawki podatku od towarów i usług (VAT)
Krzyżewska-Kubacka K., Kubacki S.
Budownictwo i Prawo
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2010
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R. 13, nr 4
38--41
7
Content available An influence matrix technique for multi-domain solution of the Navier-Stokes equations in a vorticity-streamfunction formulation
Bogusławski A., Kubacki S.
Journal of Theoretical and Applied Mechanics
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2009
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Vol. 47 nr 1
17-40
EN
The paper presents new multi-domain algorithms based on the influence matrix technique applied together with the non-overlapping iterative domain decomposition method for solution of the incompressible Navier- Stokes equations in vorticity-streamfunction formulation. The spectral Chebyshev collocation method and the influence matrix algorithm are applied for solution of the Stokes problem in each subdomain resulting from time discretization of the Navier-Stokes equations, while the patching conditions (continuity of the solution and continuity of its first order derivative) at the interfaces between subdomains are satisfied using the iterative domain decomposition algorithm.
PL
W pracy przedstawiono nowy iteracyjny algorytm dekompozycji obszaru obliczeniowego oparty na metodzie macierzy wpływu w zastosowaniu do równań Naviera- -Stokesa dla przepływu czynnika nieściśliwego w sformułowaniu wirowość-funkcja prądu. Spektralna metoda kolokacji wykorzystująca szeregi wielomianów Czebyszewa oraz metoda macierzy wpływu została zastosowana do rozwiązania zagadnienia Stokesa, będącego rezultatem dyskretyzacji równań Naviera-Stokesa w funkcji czasu, w każdym z podobszarów obszaru obliczeniowego, natomiast warunek ciągłości rozwiązania i jego pierwszej pochodnej na powierzchniach rozdziału pomiędzy podobszarami został uzyskany przy pomocy metody iteracyjnej.
8
Content available remote Dirichlet/Dirichlet and Dirichlet/Dirichlet-Neumann/Neumann non-overlapping iterative domain decomposition methods
Kubacki S., Bogusławski A.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2008
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Vol. 12, No 1-2
85-104
EN
A new iterative non-overlapping domain decomposition method is proposed for solving the one- and two-dimensional Helmholtz equation on parallel computers. The spectral collocation method is applied to solve the Helmholtz equation in each subdomain based on the Chebyshev approximation, while the patching conditions are imposed at the interfaces between subdomains through a correction, being a linear function of the space coordinates. Convergence analysis is performed for two applications of the proposed method (DDLC and DDNNLC algorithms - the meaning of these abbreviations is explained below) based on the works of Zanolli and Funaro et al. Numerical tests have been performed and results obtained using the proposed method and other iterative algorithms have been compared. Parallel performance of the multi-domain algorithms has been analyzed by decomposing the two-dimensional domain into a number of subdomains in one spatial direction. For the one-dimensional problem, convergence of the iteration process was quickly obtained using the proposed method, setting a small value of the ? constant in the Helmholtz equation. Another application of the proposed method may be an alternative to other iterative schemes when solving the two-dimensional Helmholtz equation.
9
Application of the influence matrix method for multi-domain solution of the Navier-Stokes equations
Kubacki S., Bogusławski A.
Inżynieria Chemiczna i Procesowa
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2006
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T. 27, z. 3/1
1015-1029
EN
The paper is devoted to application of the multi-domain algorithms based on the non-overlapping iterative domain decomposition method coupled with the influence matrix method for solution of the incompressible Navier-Stokes equations in vorticity-streamfunction formulation (omega-psi).
PL
Przedstawiono metodę zastosowania iteracyjnej dekompozycji obszaru obliczeniowego na podobszary nie pokrywające się w połączeniu z metodą macierzy wpływu do rozwiązania równań Naviera-Stokesa sformułowanych w postaci wirowość-funkcja prądu (omega-psi).
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