Isothermal Jet Suction Through the Lateral Openings of a Cylindrical Funnel

2010 ◽  
Vol 54 (04) ◽  
pp. 268-280
Author(s):  
Dipti P. Mishra ◽  
Sukanta K. Dash ◽  
P. Anil Kishan
Keyword(s):  
Eddy Viscosity ◽  
Unstructured Grid ◽  
Air Entrainment ◽  
Small Scale ◽  
Computational Domain ◽  
Low Velocity ◽  
Air Jet ◽  
Original Contribution ◽  
Flow Through ◽  
Suction Flow

This paper discusses the computation of air entrainment in to the louvers of a cylindrical funnel as a result of a high-velocity isothermal air jet placed inside the funnel having different lengths of protrusion and different funnel diameters. The experimental setup consists of a cylindrical Perspex tube with circular louvers cut around it. The flow through the nozzle is measured with a rotameter, and the velocity at the cylinder outlet is measured with a hot wire anemometer. The numerical simulation is carried out by solving the conservation equations of mass and momentum for the funnel with a surrounding computational domain so that the suction can take place at the louver entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two-equation k-e turbulence model of Fluent 6.3. It has been found from the experiment and the CFD computation that there exists an optimum funnel diameter for which the mass ingress into the funnel is highest, and also there exists an optimum protrusion length of the nozzle that entrains maximum air flow into the funnel. For isothermal air suction the mass ingress into the funnel does not depend on the inclination of the funnel, whereas for low velocity and high temperature of the nozzle fluid the mass ingress in to the funnel depends on the inclination of the funnel. After a critical nozzle velocity (Gr/Re2 < 0.5), the mass ingress into the funnel does not again depend on the inclination of the funnel. An approximate relation for the entrance length of a sucking pipe has also been developed from the present CFD solution. The original contribution of the paper is the setting of a computational methodology for computing various conditions of suction flow in to a funnel while having the numerical confidence by comparing the CFD result with a small-scale experimental measurement in the laboratory.

scholarly journals Multilingualism in Vanuatu: Four case studies

2021 ◽  
pp. 136700692110231
Author(s):  
Mary Walworth ◽  
Amy Dewar ◽  
Thomas Ennever ◽  
Lana Takau ◽  
Iveth Rodriguez
Keyword(s):  
Case Studies ◽  
Primary Data ◽  
Small Scale ◽  
Language History ◽  
Speech Communities ◽  
The Pacific ◽  
Historical Processes ◽  
The Social ◽  
Original Contribution ◽  
B Mobility

Each of the 65 inhabited islands of Vanuatu hosts its own unique linguistic environment in which varying degrees of multilingualism are found. This paper defines various types of small-scale multilingual settings in Vanuatu and explores what sociohistorical factors have led to them. This paper is based on first-hand observations and primary data collected by the authors in four locations in the Pacific Island nation of Vanuatu since 2016: two neighboring villages of Emae Island (Makatu and Tongamea), North Malekula, and on Maewo Island. The assessments of multilingualism in these examples from Vanuatu were qualitative, based on observations of sociolinguistic practices in each of these areas, as well as data from language history and language use surveys carried out in each place. Through defining and comparing the types of multilingualism present in the four case studies, we identify patterns in the social and historical processes that lead to various kinds of multilingualism: (a) interaction of linguistic and sociocultural identities and (b) mobility of both individuals and entire speech communities. The examples described in this paper are used to highlight the diversity of multilingualism found in Vanuatu and to explore how their differing linguistic environments and histories have contributed to their varying degrees of multilingualism. This paper makes an original contribution to knowledge about the small-scale multilingual situations in Vanuatu, offering descriptions of previously undocumented and endangered multilingual environments. Through an examination of the sociocultural motivations for multilingualism, alongside historical migrations of speaker groups and marked sociolinguistic identities, this paper contributes to research on why and how small-scale multilingualism can develop. Furthermore, this paper provides the foundation for future, more rigorous investigations into the small-scale multilingual situations of this highly understudied region.

scholarly journals Periodic flow structures in a turbofan fan stage in windmilling

2020 ◽  
pp. 095441002094829
Author(s):  
Nicolás García Rosa ◽  
Adrien Thacker ◽  
Guillaume Dufour
Keyword(s):  
Mass Flow ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Variable Mass ◽  
Flow Coefficient ◽  
Test Bed ◽  
Ambient Conditions ◽  
Low Velocity ◽  
Blade Passing Frequency ◽  
Flow Through

In a fan stage under windmilling conditions, the stator operates under negative incidence, leading to flow separation, which may present an unsteady behaviour due to rotor/stator interactions. An experimental study of the unsteady flow through the fan stage of a bypass turbofan in windmilling is proposed, using hot-wire anemometry. Windmilling conditions are reproduced in a ground engine test bed by blowing a variable mass flow through a bypass turbofan in ambient conditions. Time-averaged profiles of flow coefficient are independent of the mass flow, demonstrating the similarity of velocity triangle. Turbulence intensity profiles reveal that the high levels of turbulence production due to local shear are also independent of the inlet flow. A spectral analysis confirms that the flow is dominated by the blade passing frequency, and that the separated regions downstream of the stator amplify the fluctuations locked to the BPF without adding any new frequency. Phase-locked averaging is used to capture the periodic wakes of the rotor blades at the rotor/stator interface. A spanwise behaviour typical of flows through windmilling fans is evidenced. Through the inner sections of the fan, rotor wakes are thin and weakly turbulent, and the turbulence level remains constant through the stage. The rotor wakes thicken and become more turbulent towards the fan tip, where flow separation occurs. Downstream of the stator, maximum levels of turbulence intensity are measured in the separated flow. Large periodical zones of low velocity and high turbulence intensity are observed in the outer parts of the separated stator wake, confirming the pulsating motion of the stator flow separation, locked at the blade passing frequency. Space-time diagrams show that the flow is chorochronic, and a 2 D non-linear harmonic simulation is able to capture the main interaction modes, however, the stator incidence distribution could be affected by 3 D effects.

Coherent structures in oscillatory boundary layers

2003 ◽  
Vol 474 ◽  
pp. 1-33 ◽  
Author(s):  
PAOLA COSTAMAGNA ◽  
GIOVANNA VITTORI ◽  
PAOLO BLONDEAUX
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Vortex Structures ◽  
Small Scale ◽  
Computational Domain ◽  
Steady Flows ◽  
Low Speed ◽  
Sequence Of Events ◽  
Low Speed Streaks ◽  
Oscillatory Boundary Layers

The dynamics of the vortex structures appearing in an oscillatory boundary layer (Stokes boundary layer), when the flow departs from the laminar regime, is investigated by means of flow visualizations and a quantitative analysis of the velocity and vorticity fields. The data are obtained by means of direct numerical simulations of the Navier–Stokes and continuity equations. The wall is flat but characterized by small imperfections. The analysis is aimed at identifying points in common and differences between wall turbulence in unsteady flows and the well-investigated turbulence structure in the steady case. As in Jimenez & Moin (1991), the goal is to isolate the basic flow unit and to study its morphology and dynamics. Therefore, the computational domain is kept as small as possible.The elementary process which maintains turbulence in oscillatory boundary layers is found to be similar to that of steady flows. Indeed, when turbulence is generated, a sequence of events similar to those observed in steady boundary layers is observed. However, these events do not occur randomly in time but with a repetition time scale which is about half the period of fluid oscillations. At the end of the accelerating phases of the cycle, low-speed streaks appear close to the wall. During the early part of the decelerating phases the strength of the low-speed streaks grows. Then the streaks twist, oscillate and eventually break, originating small-scale vortices. Far from the wall, the analysis of the vorticity field has revealed the existence of a sequence of streamwise vortices of alternating circulation pumping low-speed fluid far from the wall as suggested by Sendstad & Moin (1992) for steady flows. The vortex structures observed far from the wall disappear when too small a computational domain is used, even though turbulence is self-sustaining. The present results suggest that the streak instability mechanism is the dominant mechanism generating and maintaining turbulence; no evidence of the well-known parent vortex structures spawning offspring vortices is found. Although wall imperfections are necessary to trigger transition to turbulence, the characteristics of the coherent vortex structures, for example the spacing of the low-speed streaks, are found to be independent of wall imperfections.

Prediction of Confined Coaxial Turbulent Jet Mixing With a Streamwise Differencing Scheme

1991 ◽  
Author(s):  
M. A. R. Sharif ◽  
M. A. Gadalla
Keyword(s):  
Reynolds Stresses ◽  
Low Velocity ◽  
Mean Velocity ◽  
Jet Mixing ◽  
Air Jet ◽  
Air Stream ◽  
Constant Diameter ◽  
Flow Domain ◽  
The Mean ◽  
Secondary Air

Abstract Isothermal turbulent mixing of an axisymmetric primary air jet with a low velocity annular secondary air stream inside a constant diameter cylindrical enclosure is predicted. The flow domain from the inlet to the fully developed downstream locations is considered. The predicted flow field properties include the mean velocity and pressure and the Reynolds stresses. Different velocity and diameter ratios between the primary and the secondary jets have been investigated to characterize the flow in terms of these parameters. A bounded stream-wise differencing scheme is used to minimize numerical diffusion and oscillation errors. Predictions are compared with available experimental data to back up numerical findings.

Plasma actuation effect on a NACA 4412 airfoil

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Burak Karadag ◽  
Cem Kolbakir ◽  
Ahmet Selim Durna
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Open Loop ◽  
Electrode Configuration ◽  
Small Scale ◽  
Low Velocity ◽  
Dbd Plasma ◽  
Content Type ◽  
Plasma Actuation ◽  
Electric Wind

Purpose This paper aims to investigate the effects of a dielectric barrier discharge (DBD) plasma actuator (PA) qualitatively on aerodynamic characteristics of a 3 D-printed NACA 4412 airfoil model. Design/methodology/approach Airflow visualization study was performed at a Reynolds number of 35,000 in a small-scale open-loop wind tunnel. The effect of plasma actuation on flow separation was compared for the DBD PA with four different electrode configurations at 10°, 20° and 30° angles of attack. Findings Plasma activation may delay the onset of flow separation up to 6° and decreases the boundary layer thickness. The effects of plasma diminish as the angle of attack increases. Streamwise electrode configuration, in which electric wind is produced in a direction perpendicular to the freestream, is more effective in the reattachment of the airflow compared to the spanwise electrode configuration, in which the electric wind and the free stream are in the same direction. Practical implications The Reynolds number is much smaller than that in cruise aircraft conditions; however, the results are promising for low-velocity subsonic airflows such as improving control capabilities of unmanned aerial vehicles. Originality/value Superior efficacy of spanwise-generated electric wind over streamwise-generated one is demonstrated at a very low Reynolds number. The results in the plasma aerodynamics literature can be reproduced using ultra-low-cost off-the-shelf components. This is important because high voltage power amplifiers that are frequently encountered in the literature may be prohibitively expensive especially for resource-limited university aerodynamics laboratories.

scholarly journals AxiSEM: broadband 3-D seismic wavefields in axisymmetric media

Solid Earth ◽  
2014 ◽  
Vol 5 (1) ◽  
pp. 425-445 ◽  
Author(s):  
T. Nissen-Meyer ◽  
M. van Driel ◽  
S. C. Stähler ◽  
K. Hosseini ◽  
S. Hempel ◽  
...  
Keyword(s):  
Normal Modes ◽  
Spectral Element ◽  
Multipole Expansion ◽  
Small Scale ◽  
Computational Domain ◽  
Diverse Range ◽  
Earthquake Sources ◽  
Third Dimension ◽  
Computational Resources ◽  
Background Models

Abstract. We present a methodology to compute 3-D global seismic wavefields for realistic earthquake sources in visco-elastic anisotropic media, covering applications across the observable seismic frequency band with moderate computational resources. This is accommodated by mandating axisymmetric background models that allow for a multipole expansion such that only a 2-D computational domain is needed, whereas the azimuthal third dimension is computed analytically on the fly. This dimensional collapse opens doors for storing space–time wavefields on disk that can be used to compute Fréchet sensitivity kernels for waveform tomography. We use the corresponding publicly available AxiSEM (www.axisem.info) open-source spectral-element code, demonstrate its excellent scalability on supercomputers, a diverse range of applications ranging from normal modes to small-scale lowermost mantle structures, tomographic models, and comparison with observed data, and discuss further avenues to pursue with this methodology.

scholarly journals Cloud droplet diffusional growth in homogeneous isotropic turbulence: bin microphysics versus Lagrangian superdroplet simulations

2020 ◽  
Author(s):  
Wojciech W. Grabowski ◽  
Lois Thomas
Keyword(s):  
Fluid Flow ◽  
Time Scale ◽  
Isotropic Turbulence ◽  
Spectral Width ◽  
Small Scale ◽  
Computational Domain ◽  
Homogeneous Isotropic Turbulence ◽  
Diffusional Growth ◽  
Droplet Concentration ◽  
Bin Microphysics

Abstract. Increase of the spectral width of initially monodisperse population of cloud droplets in homogeneous isotropic turbulence is investigated applying a finite-difference fluid flow model combined with either Eulerian bin microphysics or Lagrangian particle-based scheme. The turbulence is forced applying a variant of the so-called linear forcing method that maintains the mean turbulent kinetic energy (TKE) and the TKE partitioning between velocity components. The latter is important for maintaining the quasi-steady forcing of the supersaturation fluctuations that drive the increase of the spectral width. We apply a large computational domain, 643 m3, one of the domains considered in Thomas et al. (2020). The simulations apply 1 m grid length and are in the spirit of the implicit large eddy simulation (ILES), that is, with explicit small-scale dissipation provided by the model numerics. This is in contrast to the scaled-up direct numerical simulation (DNS) applied in Thomas et al. (2020). Two TKE intensities and three different droplet concentrations are considered. Analytic solutions derived in Sardina et al. (2015), valid for the case when the turbulence time scale is much larger than the droplet phase relaxation time scale, are used to guide the comparison between the two microphysics simulation techniques. The Lagrangian approach reproduces the scalings relatively well. Representing the spectral width increase in time is more challenging for the bin microphysics because appropriately high resolution in the bin space is needed. The bin width of 0.5 μm is only sufficient for the lowest droplet concentration, 26 cm−3. For the highest droplet concentration, 650 cm−3, even an order of magnitude smaller bin size is not sufficient. The scalings are not expected to be valid for the lowest droplet concentration and the high TKE case, and the two microphysics schemes represent similar departures. Finally, because the fluid flow is the same for all simulations featuring either low or high TKE, one can compare point-by-point simulation results. Such a comparison shows very close temperature and water vapor point-by-point values across the computational domain, and larger differences between simulated mean droplet radii and spectral width. The latter are explained by fundamental differences in the two simulation methodologies, numerical diffusion in the Eulerian bin approach and relatively small number of Lagrangian particles that are used in the particle-based microphysics.

The impact of ionic strength on the molecular weight distribution (MWD) of lignin dissolved during softwood kraft cooking in a flow-through reactor

Holzforschung ◽  
2016 ◽  
Vol 70 (6) ◽  
pp. 495-501 ◽  
Author(s):  
Binh T.T. Dang ◽  
Harald Brelid ◽  
Hans Theliander
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Ion Concentration ◽  
Small Scale ◽  
Kraft Cooking ◽  
Flow Through ◽  
Cooking Times ◽  
The Impact

Abstract The molecular weight distribution (MWD) of dissolved lignin as a function of time during kraft cooking of Scots pine (Pinus silvestris L) has been investigated, while the influence of sodium ion concentration ([Na+]) on the MWD was in focus. The kraft cooking was performed in a small scale flow-through reactor and the [Na+] was controlled by the addition of either Na2CO3 or NaCl. Fractions of black liquors (BL) were collected at different cooking times and the lignin was separated from the BL by acidification. The MWD of the dissolved lignin was analyzed by GPC. Results show that the weight average molecular weight (Mw) of dissolved lignin increases gradually as function of cooking time. An increase of [Na+] in the cooking liquor leads to Mw decrement. Findings from cooks with constant and varying [Na+] imply that the retarding effect of an increased [Na+] on delignification is related to the decrease in lignin solubility at higher [Na+].

Laminar and Turbulent Flow Past a Hydrofoil Predicted by a Distributed Vorticity Method

2020 ◽  
Author(s):  
Chunlin Wu ◽  
Spyros A. Kinnas
Keyword(s):  
Turbulent Flow ◽  
Eddy Viscosity ◽  
Current Method ◽  
Reynolds Numbers ◽  
Synchronous Communication ◽  
Coupling Scheme ◽  
Computational Domain ◽  
Computationally Efficient ◽  
Flow Past ◽  
Laminar And Turbulent Flow

Abstract A distributed viscous vorticity equation (VISVE) method is presented in this work to simulate the laminar and turbulent flow past a hydrofoil. The current method is proved to be more computationally efficient and spatially compact than RANS (Reynolds-Averaged Navier-Stokes) methods since this method does not require unperturbed far-field boundary conditions, which leads to a small computational domain, a small number of mesh cells, and consequently much less simulation time. To model the turbulent flow, a synchronous coupling scheme is implemented so that the VISVE method can resolve the turbulent flow by considering the eddy viscosity in the vorticity transport equation, and the eddy viscosity is obtained by coupling VISVE with the existing turbulence model of OpenFOAM, via synchronous communication. The proposed VISVE method is applied to simulate both the laminar flow at moderate Reynolds numbers and turbulent flow at high Reynolds numbers past a hydrofoil. The velocity and vorticity calculated by the coupling method agree well with the results obtained by a RANS method.

Sign in / Sign up

Export Citation Format

Share Document