A model for the effect of pressure gradient on turbulent axisymmetric wakes

2018 ◽  
Vol 837 ◽  
Author(s):  
Sina Shamsoddin ◽  
Fernando Porté-Agel
Keyword(s):  
Pressure Gradient ◽  
Practical Importance ◽  
Maximum Velocity ◽  
Analytical Framework ◽  
Momentum Equation ◽  
Self Similarity ◽  
Velocity Deficit ◽  
Starting Point ◽  
Large Eddy ◽  
Planar Strain

Turbulent axisymmetric wakes under pressure gradient have received little attention in the literature, in spite of their fundamental and practical importance, for example, in the case of wind turbine wakes over topography. In this paper, we develop an analytical framework to analyse turbulent axisymmetric wakes under different pressure gradient conditions. Specifically, we develop a model to predict how an arbitrary imposed pressure gradient perturbs the evolution of the zero-pressure-gradient wake. The starting point of the model is the basic mean conservation of the streamwise momentum equation. We take advantage of the self-similarity of the wake velocity deficit and the assumption that the ratio of the maximum velocity deficit to the wake width is independent of the pressure gradient; such an assumption is supported experimentally for planar wakes, and numerically for axisymmetric wakes in this study. Furthermore, an asymptotic solution for the problem is also derived. The problem is considered for both an axisymmetric strain and a planar strain. The inputs to the model are the imposed pressure gradient and the wake width in the zero-pressure-gradient case. To validate the model results, a set of large-eddy simulations (LES) are performed. Comparing the evolution of the maximum velocity deficit and the wake width, the model results and the LES data show good agreement. Similarly to planar wakes, it is observed that the axisymmetric wake recovers faster in the favourable pressure gradient compared with the adverse one.

Turbulent planar wakes under pressure gradient conditions

2017 ◽  
Vol 830 ◽  
Author(s):  
Sina Shamsoddin ◽  
Fernando Porté-Agel
Keyword(s):  
Pressure Gradient ◽  
Maximum Velocity ◽  
Wind Farms ◽  
Parameter Tuning ◽  
Momentum Equation ◽  
Mean Flow ◽  
Self Similarity ◽  
High Lift ◽  
Velocity Deficit ◽  
The Mean

Accurate prediction of the spatial evolution of turbulent wake flows under pressure gradient conditions is required in some engineering applications such as the design of high-lift devices and wind farms over topography. In this paper, we aim to develop an analytical model to predict the evolution of a turbulent planar wake under an arbitrary pressure gradient condition. The model is based on the cross-stream integration of the streamwise momentum equation and uses the self-similarity of the mean flow. We have also made an experimentally supported assumption that the ratio of the maximum velocity deficit to the wake width is independent of the imposed pressure gradient. The asymptotic response of the wake to the pressure gradient is also investigated. After its derivation, the model is successfully validated against experimental data by comparing the evolution of the wake width and maximum velocity deficit. The inputs of the model are the imposed pressure gradient and the wake width under zero pressure gradient. The model does not require any parameter tuning and is deemed to be practical, computationally fast, accurate enough, and therefore useful for the scientific and engineering communities.

scholarly journals Droplet impact onto a spring-supported plate: analysis and simulations

2021 ◽  
Vol 128 (1) ◽  
Author(s):  
Michael J. Negus ◽  
Matthew R. Moore ◽  
James M. Oliver ◽  
Radu Cimpeanu
Keyword(s):  
High Speed ◽  
Flexible Substrate ◽  
Practical Importance ◽  
Hybrid Approach ◽  
Hydrodynamic Pressure ◽  
Analytical Framework ◽  
Canonical System ◽  
Linear Process ◽  
Plate Motion ◽  
The Impact

AbstractThe high-speed impact of a droplet onto a flexible substrate is a highly non-linear process of practical importance, which poses formidable modelling challenges in the context of fluid–structure interaction. We present two approaches aimed at investigating the canonical system of a droplet impacting onto a rigid plate supported by a spring and a dashpot: matched asymptotic expansions and direct numerical simulation (DNS). In the former, we derive a generalisation of inviscid Wagner theory to approximate the flow behaviour during the early stages of the impact. In the latter, we perform detailed DNS designed to validate the analytical framework, as well as provide insight into later times beyond the reach of the proposed analytical model. Drawing from both methods, we observe the strong influence that the mass of the plate, resistance of the dashpot, and stiffness of the spring have on the motion of the solid, which undergo forced damped oscillations. Furthermore, we examine how the plate motion affects the dynamics of the droplet, predominantly through altering its internal hydrodynamic pressure distribution. We build on the interplay between these techniques, demonstrating that a hybrid approach leads to improved model and computational development, as well as result interpretation, across multiple length and time scales.

scholarly journals Sticky Thermals: Evidence for a Dominant Balance between Buoyancy and Drag in Cloud Updrafts

2015 ◽  
Vol 72 (8) ◽  
pp. 2890-2901 ◽  
Author(s):  
David M. Romps ◽  
Alexander B. Charn
Keyword(s):  
Large Eddy Simulation ◽  
Practical Interest ◽  
Momentum Equation ◽  
Severe Weather ◽  
Convective Clouds ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Great Practical Interest ◽  
Natural Boundaries ◽  
Drag Law

Abstract The vertical velocities of convective clouds are of great practical interest because of their influence on many phenomena, including severe weather and stratospheric moistening. However, the magnitudes of forces giving rise to these vertical velocities are poorly understood, and the dominant balance is in dispute. Here, an algorithm is used to extract thousands of cloud thermals from a large-eddy simulation of deep and tropical maritime convection. Using a streamfunction to define natural boundaries for these thermals, the dominant balance in the vertical momentum equation is revealed. Cloud thermals rise with a nearly constant speed determined by their buoyancy and the standard drag law with a drag coefficient of 0.6. Contrary to suggestions that cloud thermals might be slippery, with a dominant balance between buoyancy and acceleration, cloud thermals are found here to be sticky, with a dominant balance between buoyancy and drag.

Managing adaptive orientation systems for museum visitors from an IoT perspective

2016 ◽  
Vol 22 (2) ◽  
Author(s):  
Ludovico Solima ◽  
Maria Rosaria Della Peruta ◽  
Vincenzo Maggioni
Keyword(s):  
Design Methodology ◽  
Business Models ◽  
Communication Technologies ◽  
Analytical Framework ◽  
Digital Data ◽  
Museum Visitors ◽  
Scientific Staff ◽  
Starting Point ◽  
Potential Demand ◽  
Orientation Systems

Purpose Starting from the premises that IoT applications can be used in museums as an aid to visiting systems, the aim of this research is to see how recommendation systems can be developed to provide advanced services to museum visitors. Design/methodology/approach The research methodology employs a qualitative exploratory multi-case study: the method used has consisted in crossing the information currently known on the most advanced communication technologies (ICT) with the requirements of enhancing museum services, in order to determine the possible trajectories of applying the former to the latter Findings The implementation of recommender system outlines the main implications and effects of an advanced market-driven digital orientation, as the system’s users are the starting point for innovation and the creation of value. For a museum, it will be possible to access to an additional system of knowledge alongside that of its scientific staff. This process has profound implications in the way in which a museum presents itself and how it is perceived by its visitors and, in a wider sense, by the potential demand. Research limitations/implications Our paper consists in an exploratory effort to introduce an analytical framework for an evolved adaptive museum orientation system; the empirical investigation can be structured in the inductive-predictive view of assessing this promising debate further. Originality/value Implementing the IoT blueprint entails introducing a plethora of new products, services and business models, opening new routes to guide and direct cultural events. Now, more than ever, sustainable development involves an intrinsic balancing act between the pluralism of data and that of customer needs, which is achieved through the elaboration of digital data.

scholarly journals Pulsating Flow of an Ostwald—De Waele Fluid between Parallel Plates

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 932
Author(s):  
Rodrigo González ◽  
Aldo Tamburrino ◽  
Andrea Vacca ◽  
Michele Iervolino
Keyword(s):  
Shear Stress ◽  
Analytical Solution ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Velocity Distribution ◽  
Momentum Equation ◽  
Parallel Plates ◽  
Analytical Computation ◽  
Pulsatile Pressure ◽  
Pulsatile Pressure Gradient

The flow between two parallel plates driven by a pulsatile pressure gradient was studied analytically with a second-order velocity expansion. The resulting velocity distribution was compared with a numerical solution of the momentum equation to validate the analytical solution, with excellent agreement between the two approaches. From the velocity distribution, the analytical computation of the discharge, wall shear stress, discharge, and dispersion enhancements were also computed. The influence on the solution of the dimensionless governing parameters and of the value of the rheological index was discussed.

scholarly journals Impact of Tree Pollen Distribution on Allergic Diseases in Serbia: Evidence of Implementation of Allergen Immunotherapy to Betula verrucosa

Medicina ◽  
2020 ◽  
Vol 56 (2) ◽  
pp. 59 ◽  
Author(s):  
Rajna Minić ◽  
Mirjana Josipović ◽  
Vesna Tomić Spirić ◽  
Marija Gavrović-Jankulović ◽  
Aleksandra Perić Popadić ◽  
...  
Keyword(s):  
Allergen Immunotherapy ◽  
Practical Importance ◽  
Allergic Diseases ◽  
Pollen Concentration ◽  
Tree Pollen ◽  
Starting Point ◽  
Pollen Species ◽  
Allergenic Plants ◽  
Betula Verrucosa ◽  
The Relationship

Background and objectives: The relationship between air pollen quantity and the sensitization of allergic patients is crucial for both the diagnosis and treatment of allergic diseases. Weather conditions influence the distribution of allergenic pollen and increases in pollen concentration may negatively affect the health of allergic patients. The aim of this study was to analyze the implementation of allergen immunotherapy with regard to air pollen concentration. Material and Methods: Here we examined the relationship between Betula air pollen concentration and the usage of Betula verrucosa allergen immunotherapy in Serbia. Examination covered the period from 2015 to 2018. Measurement of airborne pollen concentration was performed with Lanzoni volumetric pollen traps. The evidence of the usage of sublingual allergen immunotherapy (SLIT) was gathered from patients with documented sensitization to specific pollen. Results: During this period tree pollens were represented with 58% ± 21% of all measured air pollen species, while Betula pollen represented 15% ± 8% of all tree pollens. Betula pollination peaked in April. Allergen immunotherapy to Betula verrucosa in Serbia is entirely conducted as sublingual immunotherapy and represents 47.1% ± 1.4% of issued tree pollen SLIT. The use of pollen SLIT increased by 68% from 2015 to 2018, with an even greater increase in usage recorded for Betula SLIT—80%. Conclusions: This analysis shows a clear causative relationship between pollination and the type/prevalence of applied allergen immunotherapy. Information about the flowering seasons of allergenic plants is very important for people who suffer from allergy, for clinical allergologists, as well as for governing authorities. The presented data is of practical importance to the proper timing of immunotherapy initiation and of importance for urban landscaping. The obtained data can be the starting point for the instatement of a thorough epidemiological study and the inclusion of Serbia on the pollen map of Europe.

scholarly journals Study of Al2O3/copper–water nanoparticle shape, slip effects, and heat transfer on steady physiological delivery of MHD hybrid nanofluid

2019 ◽  
Vol 97 (12) ◽  
pp. 1239-1252
Author(s):  
Naheeda Iftikhar ◽  
Abdul Rehman ◽  
Hina Sadaf ◽  
Saleem Iqbal
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Maximum Velocity ◽  
Yield Enhancement ◽  
Hybrid Nanofluid ◽  
Thermal Slip ◽  
Slip Parameter ◽  
Solution Flow ◽  
Shaped Nanoparticles ◽  
Uniform Tube

This paper contains the analytical investigation of magnetohydrodynamic (MHD) flow of copper/Al2O3–water hybrid nanofluid with unstable peristaltic motion. Three different geometries (bricks, cylinder, and platelets) along with velocity and thermal slip conditions are studied in detail to reach the precise solution. Flow geometry of a non-uniform tube of finite length, experimental values of base fluid, and considered nanoparticles are taken into account to examine the theoretical investigation of formulated equations. Dimensionless control equations, which are subject to physically realistic boundary conditions, are closely studied to obtain precise results. The shape effects of nanoparticles on velocity, temperature distribution, and heat transfer on the length of the non-uniform tube with variation of the various flow parameters are discussed in a graphical description to understand the theoretical aspects to validate the medical analysis. The observations from the analysis state that copper/Al2O3–water carry maximum velocity for smaller values of slip parameter. Temperature distributions for heat absorption parameter are more significant as fluid flow accelerates when large values are chosen. Large values of thermal slip parameter yield enhancement in pressure gradient and Cu–water nanofluid has higher impact than hybrid nanofluid. Platelet-shaped nanoparticles of hybrid nanofluid have more significant effect on pressure gradient than cylinder- and brick-shaped nanoparticles of Cu–water nanofluid. An intrinsic property of peristaltic transport (i.e., trapping) is also discussed. The trapped bolus decreases for platelets and cylinder-shaped nanoparticles, whereas, the size of the trapped bolus increases for brick-shaped nanoparticles. This model is applicable to a drug delivery system and to design the micro-peristaltic pump for transporting nanofluids.

Maximum Velocity Decay in a Submerged Laminar Jet Issuing from a ‘Long Tube

1983 ◽  
Vol 7 (1) ◽  
pp. 41-43 ◽  
Author(s):  
M. Arulraja ◽  
G.W. Rankin ◽  
K. Sridhar
Keyword(s):  
Velocity Profile ◽  
Maximum Velocity ◽  
Momentum Equation ◽  
Experimental Fact ◽  
Laminar Jet ◽  
Developing Region ◽  
Other Information ◽  
Velocity Decay ◽  
Matching Schemes ◽  
Jet Axis

Decay of the maximum velocity of an incompressible, axisymmetric, submerged, laminar free jel is related to the second derivative of the velocity profile at the centre line by using the momentum equation along the jet axis with boundary layer approximations. Using this decay relation and the experimental fact that the velocity profile near the jet axis remains parabolic it is shown that maximum velocity decay is linear in the developing region. The length of the developing region and the location of the virtual origin are obtained by matching the maximum velocity variations at the boundary between the developing and fully developed regions. These values are compared with the results of conventional jet matching schemes and with other information available in the literature.

Evaluation of a Statistically Targeted Forcing Method for Synthetic Turbulence Generation in Large-Eddy Simulations and Hybrid RANS-LES Simulations

2020 ◽  
Author(s):  
Olalekan O. Shobayo ◽  
D. Keith Walters
Keyword(s):  
Turbulent Flow ◽  
Momentum Equation ◽  
New Method ◽  
Navier Stokes ◽  
Model Parameters ◽  
Mean Velocity ◽  
Spectra Analysis ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Turbulence Generation

Abstract Computational fluid dynamics (CFD) results are presented for synthetic turbulence generation by a proposed statistically targeted forcing (STF) method. The new method seeks to introduce a fluctuating velocity field with a distribution of first and second moments that match a user-specified target mean velocity and Reynolds stress tensor, by incorporating deterministic time-dependent forcing terms into the momentum equation for the resolved flow. The STF method is formulated to extend the applicability of previously documented methods and provide flexibility in regions where synthetic turbulence needs to be generated or damped, for use in engineering level large-eddy and hybrid large-eddy/Reynolds-averaged Navier-Stokes CFD simulations. The objective of this study is to evaluate the performance of the proposed STF method in LES simulations of isotropic and anisotropic homogeneous turbulent flow test cases. Results are interrogated and compared to target statistical velocity and turbulent stress distributions and evaluated in terms of energy spectra. Analysis of the influence of STF model parameters, mesh resolution, and LES subgrid stress model on the results is investigated. Results show that the new method can successfully reproduce desired statistical distributions in a homogeneous turbulent flow.

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