This paper deals with studying of two topics – measuring of velocity profile deformation behind a over-flooded construction and modelling of this velocity profile deformation by computational fluid dynamics (CFD). Numerical simulations with an unsteady RANS models - Standard k-ε, Realizable k-ε, Standard k-ω and Reynolds stress models (ANSYS Fluent v.18) and experimental measurements in a laboratory flume (using ADV) were performed. Results of both approaches showed and affirmed presence of velocity profile deformation behind the obstacle, but some discrepancies between the measured and simulated values were also observed. With increasing distance from the obstacle, the differences between the simulation and the measured data increase and the results of the numerical models are no longer usable.
A graphical method of estimating bed shear from measured velocity profiles is presented as an alternative to logarithmic law approach. In the present approach the entire velocity profile is considered as per binary law of velocity distribution i.e., logarithmic law in the wall region and parabolic law in the outer region. The validity of this method has been demonstrated for a typical velocity profile. An analysis has been also made in case of an erroneous measurement of bed level. and Práca obsahuje grafickú metódu určenia charakteristík trenia na dne koryta z meraných profilov rýchlosti ako alternatívu k používanému prístupu vychádzajúcemu z logaritmického zákona rozdelenia rýchlostí prúdenia. Predložený prístup charakterizuje profil rýchlosti ako binárny, t.j. zložený z logaritmického rozdelenia v oblasti steny a z parabolického rozdelenia mimo túto oblasť. Vhodnosť tohto prístupu bola demonštrovaná pre typický rýchlostný profil. Bola vykonaná analýza aj pre nepresné meranie úrovne dna koryta.
The hydraulic characteristics of flow over rectangular broad-crested weirs with varying upstream slopes were experimentally studied. A series of laboratory experiments was performed to investigate the effects of changing upstream slopes from 90º to 75º, 60º, 45º, 30º, 22.5º, 15º, and 10º on the flow surface pattern, discharge coefficient values, approach velocity profile and flow separation zone. In addition, a new mathematical relationship for water surface profile and a new correction factor to estimate discharge coefficient over weirs with various upstream slopes were introduced. The results showed decreasing upstream slopes from 90º to 10º leading to increasing discharge coefficient values and dissipation of the separation zone. and Práca obsahuje výsledky experimentálneho štúdia prietoku vody cez pravouhlý priepad so širokou priepadovou hranou s rozdielnymi sklonmi návodného povrchu priepadu. Uskutočnili sme sériu laboratórnych pokusov s cieľom štúdia vplyvu rôznych sklonov návodného povrchu priepadu od 90°, 75°, 60°, 45°, 30°, 22,5°, 15°, až po 10° na tvar hladiny, hodnoty prietokového súčiniteľa, rýchlostné profily a na prúdenie v oblasti separácie. Okrem toho boli zistené nové matematické vzťahy na výpočet tvaru hladiny, ako aj nové korekčné faktory na určenie prietokových súčiniteľov cez priepad s rozdielnymi sklonmi návodného povrchu. Z výsledkov vyplýva, že znižujúce sa sklony návodného povrchu priepadu od 90° po 10° vedú k zvýšeniu prietokového súčiniteľa a k disipácii oblasti separácie.
This paper discusses the comparison of the flow field downstream of two different swirl generators. Both swirl generators are used to imitate the flow at the exit of the hydraulic turbine runner and study spatio-temporal behaviour of the swirling flow in the draft tube (i.e. outlet diffuser part of the hydraulic turbine), which undergoes breakdown into vortex rope. Unsteady CFD computations are carried out for identical Reynolds number. Resulting velocity and vorticity profiles are correlated with the structure of the vortex rope. Difference in excited pressure pulsations is illustrated on amplitude-frequency spectra of static wall pressure. and Obsahuje seznam literatury
The paper deals with the experimental and numerical research of flows through prismatic turbine cascade in transonic regimes. The primary goal is to evaluate the influence of the non-uniformity of the inlet velocity profile to the span-wise distribution of energy losses. The numerical simulation with inlet velocity profile corresponding to the parameters of the flow in high speed wind tunnel in Nový Knín is compared with the experimental data. and Obsahuje seznam literatury