Multiple Inlets Research Articles

Effect of multiscalar subfilter PDF models in LES of turbulent flames with inhomogeneous inlets

To apply reduced-order manifold combustion models in Large Eddy Simulations (LES) of systems with multiple inlets, it is necessary to incorporate more than one mixture fraction. As a result, the joint subfilter Probability Density Function (PDF) of the mixture fractions must be modeled. To determine the sensitivity of the predicted turbulent flame structure to these models, LES calculations of the Sydney piloted jet burner with inhomogeneous inlets have been performed using the Dirichlet, Connor-Mosimann (CM), and Beta-Delta (BD) distributions. A memory-efficient convolution-on-the-fly approach was applied to enable use of more complex subfilter PDF models, such as the CM distribution. Strong sensitivities in the LES predictions were observed to the choice of subfilter PDF model. The Dirichlet distribution was found to be ill-suited to this partially premixed turbulent flame because as a subfilter PDF model it implicitly assumes symmetric mixing in mixture fraction space, which is inconsistent with partial premixing. Good agreement with the experimental data was obtained using both the CM and BD distributions, which are mathematically consistent with partial premixing. The CM distribution is the most general of the considered distributions and gives the best predictions, but this comes with increased complexity and computational cost.

Performance analysis of a micro laminar flow fuel cell with multiple inlets of a bridge-shaped microchannel

A configuration of multiple inlets is proposed for a micro laminar flow fuel cell with a bridge-shaped channel cross section. The operation of the micro laminar flow fuel cell involves the complex interplay of electrochemical and mass transport processes. A fully coupled three-dimensional numerical model is developed to evaluate the micro laminar flow fuel cell performance. The numerical model solves the three-dimensional Navier-Stokes, mass transport, and Butler-Volmer equations for the electrode kinetics. A novel concept of multiple inlets is introduced to deal with the greater mass transport losses associated with the larger channel length. The numerical model is validated using experimental data from a micro laminar flow fuel cell with a bridge-shaped microchannel. Up to 8 inlets are tested with various bridge aspect ratios to observe the peak power and current density. The multi-inlet configurations enhance the current density by multiple times in comparison to a simple bi-inlet micro laminar flow fuel cell.

Effect of inlet modelling on surface drainage in coupled urban flood simulation

For a highly developed urban area with complete drainage systems, flood simulation is necessary for describing the flow dynamics from rainfall, to surface runoff, and to sewer flow. In this study, a coupled flood model based on diffusion wave equations was proposed to simulate one-dimensional sewer flow and two-dimensional overland flow simultaneously. The overland flow model provides details on the rainfall-runoff process to estimate the excess runoff that enters the sewer system through street inlets for sewer flow routing. Three types of inlet modelling are considered in this study, including the manhole-based approach that ignores the street inlets by draining surface water directly into manholes, the inlet-manhole approach that drains surface water into manholes that are each connected to multiple inlets, and the inlet-node approach that drains surface water into sewer nodes that are connected to individual inlets. The simulation results were compared with a high-intensity rainstorm event that occurred in 2015 in Taipei City. In the verification of the maximum flood extent, the two approaches that considered street inlets performed considerably better than that without street inlets. When considering the aforementioned models in terms of temporal flood variation, using manholes as receivers leads to an overall inefficient draining of the surface water either by the manhole-based approach or by the inlet-manhole approach. Using the inlet-node approach is more reasonable than using the inlet-manhole approach because the inlet-node approach greatly reduces the fluctuation of the sewer water level. The inlet-node approach is more efficient in draining surface water by reducing flood volume by 13% compared with the inlet-manhole approach and by 41% compared with the manhole-based approach. The results show that inlet modeling has a strong influence on drainage efficiency in coupled flood simulation.

Optimal design of an indoor environment by the CFD-based adjoint method with area-constrained topology and cluster analysis

An indoor environment should be designed to provide occupants with a desirable level of thermal comfort and air quality. The optimal design of an indoor environment can be achieved by using the computational fluid dynamics (CFD)-based adjoint method to determine the size, locations, and shape of air supply inlets, and the air supply parameters (i.e., velocity, temperature, and angle). However, the optimal design may involve a large number of air supply inlets, which would be impractical to implement. This investigation developed an area-constrained topology and cluster analysis to consolidate multiple air supply inlets into a limited number and to determine their size and locations. The desired indoor environment can be maintained by further optimizing the air supply inlet shape and parameters. This investigation demonstrated the method's capability by applying it to a two-person office and a single-aisle, fully-occupied aircraft cabin. The optimal thermal comfort conditions around the occupants can be achieved with a limited number of air supply inlets at appropriate locations.

Test of turbulence models for heat transfer within a ventilated cavity with and without an internal heat source

In this study, six of most frequently used turbulence models in computational fluid dynamics were compared with experimental data. The experimental cavity is a cube whose edge is 1 m long. The left vertical wall receives a constant and uniform heat flux, while the opposite wall is kept at a constant temperature. The rest of the walls are adiabatic. The heat source is a rectangular parallelepiped with square base 0.3 m on a side and height 0.61 m. The cavity represents a ventilated room in a 1:3 scale with multiple inlets and outlets of air, considering ventilation by ducts of an air-conditioning system. The experimental setup was built to obtain temperature profiles and heat transfer coefficients. Temperature profiles were obtained at six different depths and heights consisting of 14 thermocouples each. It was found that the lowest average of percentage differences for the case with the heat source turned on corresponds to realizable k-ε turbulence model (rkε) with 0.84%.

Multiscale Modeling and Simulation of Macromixing, Micromixing, and Crystal Size Distribution in Radial Mixers/Crystallizers

Continuous-flow tubular crystallization in which seed crystals are continuously generated is of interest due to its enabling of tighter control of crystal properties. This article is the most detailed simulation study on the design and operation of continuous-flow crystallizers using radial mixers, which have potential for inducing rapid and intense turbulent mixing and having easy construction, high reliability, and low operating costs. A multiscale model is employed that couples computational fluid dynamics (CFD), micromixing modeling, energy balance, and population balance equation (PBE) using the open-source CFD package OpenFOAM. The approach is demonstrated for the methanol–water antisolvent crystallization of lovastatin. A new crystallizer design with multiple radial inlets is proposed and shown to deliver improved mixing compared to one radial inlet. The effects of varying operating conditions on micromixing and crystal size distribution are analyzed. A systematic approach is provided for the desig...

Greenhouse gas measurements from a UK network of tall towers: technical description and first results

Abstract. A network of three tall tower measurement stations was set up in 2012 across the United Kingdom to expand measurements made at the long-term background northern hemispheric site, Mace Head, Ireland. Reliable and precise in situ greenhouse gas (GHG) analysis systems were developed and deployed at three sites in the UK with automated instrumentation measuring a suite of GHGs. The UK Deriving Emissions linked to Climate Change (UK DECC) network uses tall (165–230 m) open-lattice telecommunications towers, which provide a convenient platform for boundary layer trace gas sampling. In this paper we describe the automated measurement system and first results from the UK DECC network for CO2, CH4, N2O, SF6, CO and H2. CO2 and CH4 are measured at all of the UK DECC sites by cavity ring-down spectroscopy (CRDS) with multiple inlet heights at two of the three tall tower sites to assess for boundary layer stratification. The short-term precisions (1σ on 1 min means) of CRDS measurements at background mole fractions for January 2012 to September 2015 is < 0.05 µmol mol−1 for CO2 and < 0.3 nmol mol−1 for CH4. Repeatability of standard injections (1σ) is < 0.03 µmol mol−1 for CO2 and < 0.3 nmol mol−1 for CH4 for the same time period. N2O and SF6 are measured at three of the sites, and CO and H2 measurements are made at two of the sites, from a single inlet height using gas chromatography (GC) with an electron capture detector (ECD), flame ionisation detector (FID) or reduction gas analyser (RGA). Repeatability of individual injections (1σ) on GC and RGA instruments between January 2012 and September 2015 for CH4, N2O, SF6, CO and H2 measurements were < 2.8 nmol mol−1, < 0.4 nmol mol−1, < 0.07 pmol mol−1, < 2 nmol mol−1 and < 3 nmol mol−1, respectively. Instrumentation in the network is fully automated and includes sensors for measuring a variety of instrumental parameters such as flow, pressures, and sampling temperatures. Automated alerts are generated and emailed to site operators when instrumental parameters are not within defined set ranges. Automated instrument shutdowns occur for critical errors such as carrier gas flow rate deviations. Results from the network give good spatial and temporal coverage of atmospheric mixing ratios within the UK since early 2012. Results also show that all measured GHGs are increasing in mole fraction over the selected reporting period and, except for SF6, exhibit a seasonal trend. CO2 and CH4 also show strong diurnal cycles, with night-time maxima and daytime minima in mole fractions.

An analysis of potential controls on long-term 137Cs accumulation in the sediments of UK lakes

137Cs has been utilised extensively to investigate catchment sediment dynamics. Its activity can be indicative of sediment derived from surface sources, and its inventory in deposited sediments reflects local fallout, radioactive decay, sediment accumulation and sediment source. Lakes represent ideal depositional environments for the reconstruction of historical sediment dynamics. In the UK, depth profiles and inventories of 137Cs in lake cores have been investigated in a large number of catchments, but no study has synthesised all of these data to identify national spatial trends. The aim of this study was therefore to determine what can be learnt from 137Cs inventories and profiles from UK lakes. Analysis revealed that local reference fallout, the rate of linear sediment accumulation (cm year−1) and the lake area:catchment area ratio, are the most important factors that control lake 137Cs inventories. Delivery of mobile 137Cs to the lake shortly after fallout, dissolved in runoff, or associated with mobilised sediment in transit from the source to the lake, is also likely a major control on inventories, especially on down-core profiles and peak activities. It is possible that dissolved 137Cs inputs remain important controls on activities in recently deposited sediments, as they are often higher than potential contributing catchment sediment sources. It is also likely that finer particle-size distributions in lake-bed sediments, compared with source materials, increase both activities and inventories. Uncertainties are associated with patterns of sediment deposition on the lake bed and the estimation of local reference fallout, and lakes with low catchment-derived 137Cs inputs potentially have a comparable or lower inventory than calculated from the estimated reference fallout. Lakes with multiple inlet tributaries and poor mixing of inflows, or an irregular bed shape divided by ridges and depressions, are also likely to display considerable variability in sediment-associated 137Cs deposition. Despite these uncertainties, 137Cs depth profiles provide valuable information on sediment sources and dynamics when interpreted carefully in the context of other UK lakes, and in relation to the corresponding catchment and lake characteristics. Several distinctive down-core profiles and inventories reported here yielded valuable insights into catchment sediment dynamics.

CFD study about the effect of using multiple inlets on the efficiency of a micromixer. Assessment of the optimal inlet configuration working as a microreactor

This work deals with a 2D numerical study about the effect the number of inlets of a micromixer on the mixing efficiency when two fluids must be mixed at low Reynolds and high Schmidt numbers. In this study, 6 different inlet configurations (with 2, 3, 4, 5, 6 and 7 inlets) for 2 Reynolds (0.1 and 0.29) and 3 Schmidt numbers (10 × 103, 4 × 103 and 2 × 103) have been considered. Just as reference micromixer and for comparative purposes, the geometry studied in Ortega-Casanova (2017), with just 2 inlets, has been now redesigned with more inlets incorporated. Originally, the micromixer with 2 inlets, Re = 0.29 and Sc = 10 × 103 gave a mixing efficiency of ∼14%, while we show in this work that with 7 inlets and the same Reynolds number, the efficiency can be increased up to ∼80%, when Sc = 10 × 103, and up to ∼95%, when Sc = 2 ×103. Later, we show that the mixing cost of the optimal inlet configuration is one of the lowest in comparison with previous works. Additionally, when the optimal configuration is used as microreactor, the reacting efficiency also increases in comparison with the 2-inlet configuration. We also estimate the number of inlets for full and complete mixing.

Experimental research in rotating wedge-shaped cooling channel with multiple non-equant holes lateral inlet

The heat transfer in a novel smooth wedge-shaped cooling channel with lateral ejection of turbine blade trailing edge is experimentally investigated in both non-rotating and rotating cases. Beside the conventional inlet at the bottom of the channel, an extra coolant injection from 8 lateral non-equant holes is introduced to improve the overall heat transfer. The total mass flow rate ratio (lateral mass flow rate/total mass flow rate) varies from 0 to 1.0. The major inlet Reynolds number and rotation number respectively vary from 10000 to 20000 and from 0 to 1.16. Experimental results show that the lateral inlet decreases local bulk temperature and increases local heat transfer at the middle and the top of the static channel. In rotating cases, the lateral inlet notably improves the heat transfer at the high-radius half channel and compensates the negative effects induced by the rotation. Both intensity and uniformity of heat transfer inside the channel are enhanced while flow resistance decreases with proper mass flow rate ratio of coolant from two inlets. The most satisfactory total mass flow rate ratio is around 2/3. This new structural style of cooling channel has huge potential and provides new direction of heat transfer of turbine blade trailing edge.

Tidal and subtidal exchange flows at an inlet of the Wadden Sea

Observations of underway velocity profiles during complete spring and neap tidal cycles were used to determine whether the spatial structures of tidal and subtidal flows at a tidal inlet in a multiple-inlet embayment are consistent with those observed at single-inlet embayments. Measurements were obtained at the Otzumer Balje, one of the multiple inlets among the East Frisian Islands of the Wadden Sea. The 1.5 km-wide inlet displayed a bathymetric profile consisting of a channel ∼15 m deep flanked by <5 m shoals. Neap tide observations spanned 36 h in the period May 11–12, 2011, while spring tide measurements exceeded 48 h from May 17 to May 19, 2011. Analysis of observations indicate that frictional effects from bathymetry molded tidal flows. Spatial distributions of semidiurnal tidal current amplitude and phase conform to those predicted by an analytical model for a basin with one inlet. Maximum semidiurnal flows appear at the surface in the channel, furthest away from bottom friction effects. Therefore, Otzumer Balje displays tidal hydrodynamics that are independent of the other inlets of the embayment. Subtidal exchange flows are laterally sheared, with residual inflow in the channel combined with outflow over shoals. The spatial distribution of these residual flows follow theoretical expectations of tidally driven flows interacting with bathymetry. Such distribution is similar to the tidal residual circulation at other inlets with only one communication to the ocean, suggesting that at subtidal scales the Otzumer Balje responds to tidal forcing independently of the other inlets.

Simulation and optimization of fixed bed solid acid catalyzed isobutane/2-butene alkylation process

The isobutane/2-butene alkylation process using fixed bed arrays as reactors and β-zeolite as the catalyst is simulated and analyzed. By employing the Lagrange’s method, numerical problems that originate from nonlinear reactions and Eulerian girds are neutralized. Sensitivity of operating parameters on process performance are discussed, such as paraffin/olefine ratio, alkylate reflux ratio and liquid velocity. It is found that larger paraffin/olefine is required for greater olefine to alkylate selectiviy. And alkylate reflux is also necessary to save energy cost in the distillation operations. Alternative configurations such as multiple inlet points and radical bed are discussed. To determine the optimal operating parameters, a techno-economical model is established and optimized. In the final analysis, guidelines for the further design of solid acid catalyzed alkylation process are presented.

Sediment transport and shoreline shifts in response to climate change at the tidal inlets of Chilika, India

The shoreline adjoining Chilika Lake, situated along India’s east coast, has multiple tidal inlets which connect the lake with Bay of Bengal. The shoreline behavior near such inlets is generally studied with the help of a suitable numerical model. Such models are run on the basis of historical data of waves and other information. However, the waves in future may show different strength and pattern than the past as a result of the climate change induced by global warming. It is thus necessary that the model input should correspond to future or projected data of wind and waves. In this work, we have used the wind information from a state-of-the-art regional climate model, CORDEX RegCM-4, of future 25 years in order to run a shoreline evolution model and have derived the longshore sediment transport rate as well as the shoreline change rate around Chilika inlets. These future values are compared with corresponding ones of the past 25 years. It is found that at the given location, mean wind might go up by 20%, and this could raise the mean significant wave height strongly by 32%. The direction and frequency of occurrence of waves would also change, and this in turn will cause an increase in the net littoral drift by 41% and net accumulated drift over the entire cross-shore width by 84%. Interestingly, the present site where accretion was prevalent in the past may see erosion in future at the rate of about 1 m per year.

Residual generation for leakage signatures in water supply networks with multiple inlets

Water scarcity is becoming an increasing problem worldwide, and an issue compounding the problem is water leakage in the piping networks delivering potable/consumable water to end-users (Sensus, 2012). In this paper, we consider the problem of generating a set of residuals for detecting and potentially isolating leakages in water supply networks with multiple inlets using reduced network models. Using a reduced order model of the network, the expected behaviour of the network can be estimated and then compared with actual measurements obtained from the network. The result of this comparison is a set of residuals which can be used to isolate a potential leakage. As the reduced order model is adaptive based on measurements from the network, the method is plug-and-play commissionable. In the current paper, we only consider sudden leakages as the model adaptation means that slowly developing leakages will be adapted into the parameters of the model.

Experimental and numerical study of turbulent mixed convection in a cavity with an internal heat source

In this study, experimental and numerical results of heat transfer in a ventilated cavity with an internal heat source are presented. The cavity represents a ventilated room with a person inside in a 1:3 scale. It has a vertical wall receiving a constant and uniform heat flux, while the opposite wall is kept at a constant temperature. The rest of the walls is adiabatic. The cavity has multiple inlets and outlets of air, considering ventilation by ducts of an air-conditioning system. Experimental temperature profiles were obtained at six different depths and heights consisting of 14 thermocouples each. Six turbulence models were evaluated against experimental data. The minimum average percentage differences between numerical and experimental average Nusselt numbers of the hot wall and heat source were 12.9% and 4.1% with the renormalized k–ε turbulence model.

Trapped Cylindrical Flow With Multiple Inlets for Savonius Vertical Axis Wind Turbines

Savonius vertical axis wind turbines (VAWTs) typically suffer from low efficiency due to detrimental drag production during one half of the rotational cycle. The present study examines a stator assembly created with the objective of trapping cylindrical flow for application in a Savonius VAWT. While stator assemblies have been studied in situ around Savonius rotors in the past, they have never been isolated from the rotor to determine the physics of the flow field, raising the likelihood that a moving rotor could cover up deficiencies attributable to the stator design. The flow field created by a stator assembly, sans rotor, is studied computationally using three-dimensional (3D) numerical simulations in the commercial computational fluid dynamics (CFD) package Star-CCM+. Examination of the velocity and pressure contours at the central stator plane shows that the maximum induced velocity exceeded the freestream velocity by 65%. However, flow is not sufficiently trapped in the stator assembly, with excess leakage occurring between the stator blades due to adverse pressure gradients and momentum loss from induced vorticity. A parametric study was conducted on the effect of the number of stator blades with simulations conducted with 6, 12, and 24 blades. Reducing the blade number resulted in a reduction in the cohesiveness of the internal swirling flow structure and increased the leakage of flow through the stator. Two unique energy loss mechanisms have been identified with both caused by adverse pressure gradients induced by the stator.

Analysis and Optimization of Inlet and Outlet Boundary Conditions for Flow Simulations in Circle of Willis

AbstractBlood flow simulation of complex arterial networks in three‐dimensions generally involves assigning multiple inlets and outlets. This work investigates different kinds of boundary condition assigned on inlets and outlets in the Circle of Willis. These boundary conditions will be adopted in a way that a realistic velocity profile and pressure in the main brain arteries are achieved. The result of this work will be used for Fluid–structure interaction simulations. As the force applied on the artery wall depends on the blood pressure, the goal is to achieve a pressure boundary condition based on the in‐vivo flow rates in each artery. (© 2017 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Numerical study on the effects of multiple inlet slot configurations on swirl cooling of a gas turbine blade leading edge

In this paper, a cylindrical swirl chamber, which can be used on the leading edge of a turbine blade is numerically modeled to investigate the effects of multiple slots at each section of the swirl chamber. The RANS equations are solved using four different turbulence models, and it was found that the SST k−ω model, resulted in the reasonable agreement with the experimental data. Two different chamber types, i.e., swirl chamber (SC) and double swirl chamber (DSC), are considered to be modeled with five different inlet configurations. In all configurations, rectangular inlet slots are located at the beginning and middle sections of the swirl chamber, but the number and direction of inlet slots will change in each configuration. SC and DSC configurations are compared using two different scenarios, where the width of both chamber types are identical in the first scenario and the hydraulic diameters are assumed to be identical in the next one. It is concluded that the comparison according to the identical width is more reasonable in the case of gas turbine blades. Results for the same Reynolds number and coolant mass flow rate confirm that the multiple inlets at each section with proper direction creates stronger vortices, which enhances the Nusselt number by 33% as compared to the base inlet configuration.

Measurement and simulation of the three-dimensional flow pattern and particle removal efficiencies in a large floating closed sea cage with multiple inlets and drains

This study investigated the three-dimensional flow structures in an ellipsoid, closed sea fish cage. The results are presented using computational fluid dynamics (CFD) simulations and experimental measurements. Experimental residence time distribution (RTD) measurement and CFD simulation are the best methods to study the hydrodynamics of inflow systems. Three-dimensional numerical simulations of the flow and transport characteristics of the system were conducted using a Reynolds-averaged Navier-Stokes equation approach and the results were compared to the measurements performed using acoustic Doppler velocimetry techniques. The objective of the investigation was to characterize the flow field generated in an ellipsoid, closed tank. The flow in the enclosed volume is driven by four inlets pipes integrated into the wall of the cage. The focus is on the turbulent structures and undesirable flow patterns that lead to reduced self-cleaning efficiency and a lower quality habitat for the fish through phenomena, such as recirculation zones or low velocity areas. Correlations between CFD and the experimental data confirm the adequate reproduction of hydrodynamic conditions and reinforce the predictive capabilities of numerical models as tools to simulate field scale closed containment systems or to optimize existing and future aquaculture designs. The simulation of aquaculture-like particles demonstrates that almost 100% of particles with a diameter ranging between 1μm and 3000μm are removed during a maximum of two hydraulic retention time (HRT) cycles. Smaller particles are removed via the upper-side outlets and larger particles are removed via the bottom outlet.

Cold Front Driven Flows Through Multiple Inlets of Lake Pontchartrain Estuary

AbstractWith in situ observations using acoustic Doppler current profilers (ADCPs) and numerical experiments using the Finite Volume Coastal Ocean Model (FVCOM), this study investigates atmospheric cold front induced exchange of water between Lake Pontchartrain Estuary and coastal ocean through multiple inlets. Results show that the subtidal hydrodynamic response is highly correlated with meteorological parameters. Northerly and westerly winds tend to push water out of Lake Pontchartrain, while south and east winds tend to produce currents flowing into it. For most cases, the subtidal water level is inversely correlated with the east wind, with the correlation coefficient being ∼0.8. The most important finding of this work is that, contrary to intuition, the cold front induced remote wind effect has the greatest contribution to the overall water level variation, while the local wind stress determines the surface slope inside the estuary. It is found that wind driven flow is roughly quasi steady state: the surface slope in the north‐south direction is determined by the north‐south wind stress, explaining ∼83% of the variability but less so in the east‐west direction (∼43%). In other words, the north‐south local wind stress determines the water level gradient in that direction in the estuary while the overall water level change is pretty much controlled by the open boundary which is the “remote wind effect,” a regional response that can be illustrated only by a numerical model for a much larger area encompassing the estuary.