scholarly journals Turbine flowmeter response to transitional flow regimes

2018 ◽  
Vol 59 ◽  
pp. 18-22 ◽  
Author(s):  
Zijad Džemić ◽  
Brane Širok ◽  
Benjamin Bizjan
Keyword(s):  
Flow Regimes ◽  
Transitional Flow ◽  
Turbine Flowmeter

A Functional Scaling Relationship for Laminar to Turbulent Flow Regimes

2011 ◽  
Author(s):  
George Papadopoulos
Keyword(s):  
Turbulent Flow ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Flow Characteristics ◽  
Flow Region ◽  
Flow Regimes ◽  
Transitional Flow ◽  
Turbulent Regime ◽  
Flow Profile ◽  
Scaling Relationship

A dimensional analysis that is based on the scaling of the two-dimensional Navier-Stokes equations is presented for correlating bulk flow characteristics arising from a variety of initial conditions. The analysis yields a functional relationship between the characteristic variable of the flow region and the Reynolds number for each of the two independent flow regimes. A linear relationship is realized for the laminar regime, while a nonlinear relationship is realized for the turbulent regime. Both relationships incorporate mass-flow profile characteristics to fully capture the effects of initial conditions on the variation of the characteristic variables. The union of these two independent relationships is formed utilizing the concept of flow intermittency to further expand into a generic scaling relationship that incorporates transitional flow effects to fully encompass solutions spanning the laminar to turbulent flow regimes. The results of the analysis are discussed within the context of several flow phenomena (e.g. pipe flow, jet flow & separated flow) resulting from various initial and boundary conditions.

Numerical modelling of the molecular and transitional flow regimes in vacuum components

Vacuum ◽  
1995 ◽  
Vol 46 (8-10) ◽  
pp. 863-866 ◽  
Author(s):  
Godela Scherer-Abreu ◽  
Raul A Abreu
Keyword(s):  
Numerical Modelling ◽  
Flow Regimes ◽  
Transitional Flow

scholarly journals Dynamical flow characterization of transitional and chaotic regimes in converging–diverging channels

1996 ◽  
Vol 321 ◽  
pp. 25-57 ◽  
Author(s):  
A. M. Guzmán ◽  
C. H. Amon
Keyword(s):  
Fractal Dimensions ◽  
Flow Regimes ◽  
Transitional Flow ◽  
Autocorrelation Functions ◽  
Chaotic Flows ◽  
Chaotic Flow ◽  
Onset Of Chaos ◽  
Flow Characterization ◽  
Dynamical Flow

Numerical investigation of laminar, transitional and chaotic flows in converging–diverging channels are performed by direct numerical simulations in the Reynolds number range 10 < Re < 850. The temporal flow evolution and the onset of turbulence are investigated by combining classical fluid dynamics representations with dynamical system flow characterizations. Modern dynamical system techniques such as timedelay reconstructions of pseudophase spaces, autocorrelation functions, fractal dimensions and Eulerian Lyapunov exponents are used for the dynamical flow characterization of laminar, transitional and chaotic flow regimes. As a consequence of these flow characterizations, it is verified that the transitional flow evolves through intermediate states of periodicity, two-frequency quasi-periodicity, frequency-locking periodicity, and multiple-frequency quasi-periodicity before reaching a non-periodic unpredictable behaviour corresponding to low-dimensional deterministic chaos.Qualitative and quantitative differences in Eulerian dynamical flow parameters are identified to determine the predictability of transitional flows and to characterize chaotic, weak turbulent flows in converging–diverging channels. Autocorrelation functions, pseudophase space representations and Poincaré maps are used for the qualitative identification of chaotic flows, assertion of their unpredictable nature, and recognition of the topological structure of the attractors for different flow regimes. The predictability of transitional flows is determined by analysing the autocorrelation functions and by representing their attractors in the reconstructed pseudophase spaces. The transitional flow behaviour is examined by the geometric visualization of the evolution of the attractors and Poincaré maps until the appearance of a strange attractor at the onset of chaos. Eulerian Lyapunov exponents and fractal dimensions are quantitative parameters to establish the onset of chaos, the persistence of chaotic flow behaviour, and the long-term persistent unpredictability of chaotic Eulerian flow regimes. Lastly, three-dimensional simulations for converging–diverging channel flow are performed to determine the effect of the spanwise direction on the route of transition to chaos.

Flow Bifurcations and Heat Transfer Enhancement in Asymmetric Grooved Channels

2005 ◽  
Author(s):  
Amador M. Guzma´n ◽  
Fernando A. Villar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Regime ◽  
Flow Regimes ◽  
Numerical Results ◽  
Transitional Flow ◽  
Periodic Flow ◽  
Transfer Enhancement ◽  
Transition Scenario

Numerical investigations of the flow bifurcations, transition scenario and heat transfer enhancement in asymmetric grooved channels are performed by direct numerical simulations of the mass, momentum and energy equations. The governing equations are solved for laminar and time-dependent transitional flow regimes by the spectral element method in a periodic computational domain with appropriated boundary conditions. Numerical results show a flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively. Fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from a laminar to higher transitional flow regime. Numerical calculations demonstrate that the time-average mean Nusselt number (the non-dimensional heat transfer rate), increases significantly as the flow passes from a laminar to a periodic—and then to a quasi-periodic flow regime. This increase is accompanied by a reasonable increase in both the friction factor and the pumping power. The obtained behavior is comparable to other geometries and configurations as well as to previously reported numerical results for the studied geometry. This numerical investigation shows a transition scenario at the onset of turbulence, similar to the Ruelle-Takens-Newhouse scenario, which has not been found or reported by other researchers using this geometry. The numerical simulation results also show the existence of a bifurcation scenario that develops a path-dependent flow and heat transport behavior. In the vicinity of the first Hopf flow bifurcation (and consequently, the critical Reynolds number Rec1), the resulting stable time periodic flow depends on both the initial flow conditions and the way in which the incremental process to higher flow regimes is carried out.

Sign in / Sign up

Export Citation Format

Share Document