Flow Penetration Research Articles

Dispersion and upwind-side shear-layer characteristics of forward-inclined transverse jet in crossflow

The effects of the forward inclination of a jet in crossflow on the jet fluid dispersion and upwind-side shear-layer characteristics were studied experimentally in an open-loop wind tunnel. The jet forward-inclination angle θ was varied from 0° to 50°, and the jet-to-crossflow momentum–flux ratio was adjusted between 1 and 2. Short- and long-exposure flow patterns were examined using the laser-assisted smoke flow visualization technique. The binary edge-detection technique was applied to the long-exposure flow images to obtain the jet penetration height. The instantaneous velocities in the upwind-side shear layer of the bent jet were captured by a hot-wire anemometer through a high-speed data acquisition system. The fast Fourier transform method was used to convert the instantaneous velocities from time to the frequency domain. Transverse dispersion of the jet fluids and jet trajectories described by the maximum jet-fluid concentrations were determined using the tracer-gas concentration detection method. The results revealed that at the same jet-to-crossflow momentum–flux ratio, a forward inclination did not significantly influence the flow characteristics and dispersion properties when the inclination angle was smaller than about 12°. At moderate forward inclinations (about 12°–42°), the upstream-side coherent flow structures appeared periodically. The penetration height, transverse width, and dispersion of jet fluids were greater than those of the elevated transverse jet and the slightly forward-inclined transverse jet. At forward inclinations larger than about 42°, the upstream-side coherent flow structures, penetration height, transverse width, and dispersion of jet fluids became the largest when compared with those of the elevated transverse jet as well as the slight and moderate inclination ranges. The jet trajectories in the moderate and large inclination ranges were located at transverse levels higher than those in the slight inclination range and elevated transverse jet due to the appearance of the large upwind-side shear-layer coherent flow structures. The effects of the forward inclinations on the time and length scales of the upwind-side coherent flow structures and the time and length scales of the turbulent eddies were presented and discussed.

Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior.

The rheological behavior of cement paste and the improvement of its flowability takes center stage in many research projects. An improved flowability can be achieved by the addition of superplasticizers (SP), such as polycarboxylate ethers (PCE). In order to be able to use these PCEs effectively and in a variety of ways and to make them resistant to changes in the environment, it is crucial to understand the influence of SPs on cement hydration. For that reason, the topic of this paper was the incompatibility of a specific SP and an ordinary Portland cement (OPC). The incompatible behavior was analyzed using rheological tests, such as the spread flow test and penetration test, and the behavior was compared by means of an ultrasound technique and explained by the phase content measured by in-situ X-ray diffraction (XRD) the heat evolution measured by calorimetry, and scanning electron microscope (SEM) images. We showed that the addition of the SP in a high dosage led to a prevention of the passivation of the most reactive and aluminum-containing clinker phases, aluminate and brownmillerite. This induced the aluminate reaction to take place in the initial period and led to an immediate stiffening of the cement paste and, therefore, to the complete loss of workability. The results showed that in addition to the ettringite, which began to form directly after water addition, hemicarbonate precipitated. The fast stiffening of the paste could be prevented by delayed addition of the SP or by additional gypsum. This fast stiffening was not desirable for SPs, but in other fields, for example, 3D printing, this undesirable interaction could be used to improve the properties of printable mortar.

Numerical study of fluid flow and heat transfer characteristics of an oscillating porous circular cylinder in crossflow

In this paper, numerical simulation of fluid flow and heat transfer characteristics of a porous cylinder subjected to a transverse oscillation in subcritical crossflow are studied for the first time. As such, the effects of Darcy number, 10−6 ≤ Da ≤ 10−2, reduced frequency, 0.2688 ≤ f* ≤ 1.075, dimensionless amplitude, A/d = 0.5 and 1, and Reynolds number, 5 ≤ Re ≤ 40, on the problem are investigated. It is revealed by the results that for an oscillating porous cylinder even at the subcritical Reynolds number of 40, the vortex shedding surprisingly develops behind the cylinder for cases with Da ≤ 10−4, f* = 1.075, and A/d = 1. Furthermore, it is shown that this subcritical vortex shedding always happens at the lock-in situation. The oscillation of the cylinder is shown to always increase the lift and drag coefficients compared to the stationary cylinder. According to the results, interestingly, the average drag coefficient increases with increasing Darcy number at intermediate Darcy numbers (10−4 ≤ Da ≤ 10−3). It is concluded that two mechanisms boost the heat transfer rate, namely, the vortex shedding, which is the case for the low Darcy zone at the highest frequency and amplitude of the oscillation, and the flow penetration, which is of more importance to the high Darcy zone. In conclusion, the maximum increase in the average Nusselt number is achieved at the highest values of the frequency and amplitude, which provide 18%, 28%, 51%, and 81% heat transfer enhancement compared to the stationary cylinder for Da = 10−6, 10−4, 10−3, and 10−2, respectively.

Experimental evidence of amplitude modulation in permeable-wall turbulence

The dynamic interplay between surface and subsurface flow in the presence of a permeable boundary was investigated using low and high frame-rate particle-image velocimetry measurements in a refractive-index-matching flow environment. Two idealized permeable wall models were considered. Both models contained five layers of cubically packed spheres, but one exhibited a smooth interface with the flow, while the other embodied a hemispherical surface topography. The relationship between the large-scale turbulent motions overlying the permeable walls and the small-scale turbulence just above, and within, the walls was explored using instantaneous and statistical analyses. Although previous studies have indirectly identified the potential existence of amplitude modulation in permeable-wall turbulence (a phenomenon identified in impermeable-wall turbulence whereby the outer large scales modulate the intensity of the near-wall, small-scale turbulence), the present effort provides direct evidence of its existence in flow over both permeable walls considered. The spatio-temporal signatures of amplitude modulation were also characterized using conditional averaging based on zero-crossing events. This analysis highlights the connection between large-scale regions of high/low streamwise momentum in the surface flow, downwelling/upwelling across the permeable interface and enhancement/suppression of small-scale turbulence, respectively, just above and within the permeable walls. The presence of bed roughness is found to intensify the strength and penetration of flow into the permeable bed modulated by large-scale structures in the surface flow, and linked to possible roughness-formed channelling effects and shedding of smaller-scale flow structures from the roughness elements.

Bio-optical characterization of the waters of the Bay of La Paz, southern Gulf of California, during late spring 2004

Information on selected bio-optical properties and primary production values of the waters of the Bay of La Paz, southern Gulf of California, is reported during June 2004, a region characterized to have very rich biodiversity, including endemic and endangered species, with high ecological relevance. In-situ measurements of natural fluorescence and photosynthetically available radiation (PAR) enabled the subsequent calculation of the incident irradiance (E0), the light extinction coefficient (k), compensation depth (Zc) and critical depth (Zcr). The results suggest the presence of light propitious conditions for phytoplankton community growth and net primary production, which are highly significant for the potential development of models of light penetration, ocean color, primary productivity, and analyses of organic carbon energy flow.

Numerical modelling of fluid flow and weld penetration in activated TIG welding

This research work emphasis on understanding the weld pool development while carrying out Activated Tungsten Inert Gas (A-TIG) welding by employing Computational Fluid Dynamics (CFD). The influence of temperature coefficient of surface tension (∂γ/∂T) and the concentration of oxygen, the main surface active component on weld bead geometry is studied. A three-dimensional (3D) numerical model has been developed for A-TIG welding process with varying oxygen levels employing ANSYS Fluent for 316LN stainless steel. The general conservation equations consisting mass, energy and momentum were solved in order to acquire the temperature and velocity fields with oxygen levels varying from 50 to 300 ppm in weld pool. The impact of driving forces particularly buoyancy and Marangoni on the weld pool convection were examined. The simulation confirmed that the weld bead shape was influenced mainly by Marangoni convection consecutively dependent on the oxygen content in the weld metal in the course of A-TIG welding. The addition in oxygen content changes the surface tension temperature coefficient ∂γ/∂T from negative to positive gradient causing inward flow. It was found that minor oxygen content in the molten pool until 150 ppm exhibited outward flow and with higher oxygen content beyond 150 ppm exhibited an inward flow. The oxygen content in the weld bead without flux and with flux was found to be 69 and 336 ppm respectively for the type 316LN stainless steel plates welded by A-TIG welding. The simulated weld bead profile was validated by comparing with the experimentally obtained weld bead profile. There was excellent agreement between the two weld bead profiles.

An experimental and numerical investigation of forced convection in high porosity aluminum foams subjected to jet array impingement in channel-flow

This paper reports an experimental and numerical investigation on flow and thermal transport in high porosity aluminum foams (ε~0.94–0.96) placed in a channel of square cross-section and subjected to jet array (5 × 5) impingement. The plate issuing the jets was flushed with the metal foam face. Experiments were conducted for three different values of jet-to-jet spacing (x/dj=y/dj) of 2, 3 and 5, and three foam samples with pore-densities 10, 20, and 40 PPI (pores per inch). Values of steady-state heat transfer rate and pressure drop were calculated for Reynolds number (based on channel hydraulic diameter and channel inlet velocity) ranging from 2500 to 13,500. The main findings are as follows: first, for all the test runs, the impingement configurations had higher heat transfer rate, h, compared to that for the baseline configuration of metal foams in a channel flow. Second, for all values of the jet-to-jet spacing, an increase in pore-density was accompanied by an increase in heat transfer. The enhancement (h/h0) varied between 26 and 48, with the highest gain observed for the widest jet (x/d=2) and the highest pore density (40 ppi) configuration, where h0 is the heat transfer coefficient for developed turbulent flow in a circular duct. The numerical computations reveal interesting recirculating flow structures immediately downstream of the jet exits and the extent of flow penetrating in the foam. Collectively, these flow patterns play a dominant role in determining the volume of metal foam volume participating in the thermal transport and the net convective heat transfer rate.

An experimental and numerical study of natural gas jets for direct injection internal combustion engines

Natural gas predominantly contains methane which is the cleanest burning hydrocarbon. It can be considered as the most promising alternative fuel that has the potential to replace gasoline and diesel. This is mainly due to wider availability, lower fuel price, favourable fuel properties and cleaner burning characteristics. Currently in all spark ignited CNG engines fuel is port injected that results in lower peak torque due to reduced volumetric efficiency. Direct injection can easily overcome this drawback and can match the performance levels of modern gasoline direct injection engines while emitting far less harmful pollutants. Gaseous direct injection produces highly diffusive under-expanded turbulent gaseous jets. In order to optimise mixture preparation and maximise combustion performance, the flow characteristics of gaseous jets need to be further understood and modelled. In this work, the fundamentals of gaseous flow from an outward opening direct injector is studied. Schlieren imaging is used at high spatial and temporal resolution to characterise the far-field jet growth. The nozzle in a typical outward opening direct injector has been found to produce a hollow conical jet at the beginning of injection which later collapses depending on the nozzle geometry and pressure ratio. The experimental data are used to validate a CFD model. A numerical investigation is carried out to predict the jet growth for different nozzle geometries and their effect on the jet characteristics such as mass flow rate, penetration and mixing is discussed.

Clinical value of serum hyaluronan and propeptide of type III collagen in patients with pancreatic cancer.

Hyaluronan (HA) and collagen are highly expressed in pancreatic cancer (PC) stroma. HA and collagen accumulation increase tumor interstitial fluid pressure, compromising blood flow and drug penetration. The aim of this biomarker study was to determine the clinical utility of serum HA and the propeptide of type III collagen (PRO-C3) in patients with PC. A cohort from the Danish BIOPAC study (NCT03311776) including patients with histologically confirmed pancreatic ductal adenocarcinoma (n = 809), ampullary carcinoma (n = 44), distal biliary tract cancer (n = 31), chronic pancreatitis (n = 15), intraductal papillary mucinous neoplasm (n = 41), duodenal adenoma (n = 7) and no cancer (n = 25). Healthy controls were available for serum HA (n = 141) and PRO-C3 (n = 8). The main outcome was overall survival (OS) of patients with PC in relation to pretreatment serum HA and PRO-C3 levels. Patients with PC had higher baseline serum HA and PRO-C3 than healthy subjects and patients with benign conditions. Pretreatment serum baseline HA and PRO-C3 in patients with PC were associated with poorer survival and PRO-C3 remained prognostic also after adjusting for age, performance status, stage, the presence of liver and peritoneum metastasis, and CA19-9. Detection of HA and PRO-C3 may be useful in differentiating between malignant and benign pancreatic conditions. Serum HA and PRO-C3 were prognostic for OS in patients with PC.

Large-Eddy Simulation and RANS Analysis of the End-Wall Flow in a Linear Low-Pressure Turbine Cascade, Part I: Flow and Secondary Vorticity Fields Under Varying Inlet Condition

Abstract In low-pressure turbines (LPTs), around 60–70% of losses are generated away from end-walls, while the remaining 30–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Experimental and numerical studies have shown how the strength and penetration of the secondary flow depends on the characteristics of the incoming end-wall boundary layer. Experimental techniques did shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving computational fluid dynamics (CFD) allowed to dive deep into the details of the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 LPT profile at Re = 120 K and M = 0.59 by benchmarking with experiments and investigating the impact of the incoming boundary layer state. The simulations are carried out with proven Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) solvers to determine if Reynolds-averaged models can capture the relevant flow details with enough accuracy to drive the design of this flow region. Part I of the paper focuses on the critical grid needs to ensure accurate LES and on the analysis of the overall time-averaged flow field and comparison between RANS, LES, and measurements when available. In particular, the growth of secondary flow features, the trace and strength of the secondary vortex system, and its impact on the blade load variation along the span and end-wall flow visualizations are analyzed. The ability of LES and RANS to accurately predict the secondary flows is discussed together with the implications this has on design.

Direct Nanoscopic Measurement of Laminar Slip Flow Penetration of Deformable Polymer Brush Surfaces: Synergistic Effect of Grafting Density and Solvent Quality.

A detailed quantitative nanoscopic description of soft surfaces under dynamic flow is lacking, despite its importance. To better understand the role of surface texture in nanoscopic mass transport in complex media, we used Förster resonance energy transfer in combination with total internal reflectance fluorescence microscopy (FRET-TIRFM) to directly measure laminar slip flow penetration depth (slip length) on poly(N-isopropylacrylamide) (pNIPAM) thin films (50-110 nm) of different grafting densities (0.60, 0.38, and 0.27 chain/nm2) in solvents of different qualities created via cononsolvency in situ. Nontrivial synergistic interplay of grafting density and solvent quality on slip length was observed. Slip lengths are typically tens of nm (40-100 nm), increasing and then reaching a plateau with applied linear flow velocity (192-2,952 μm/s) regardless of experimental system. Slip length was systematically larger for lower density films, but the effect of grafting density was more significant in a good solvent than a poor solvent. Interestingly, however, the stagnant film thickness (polymer swollen thickness minus the slip length) collapsed to almost a singular value for a given grafting density regardless of solvent quality, likely suggesting a large gradient of segmental mobility at nonequilibrium. Moreover, we found that slip flow penetrates into soft pNIPAM surfaces more deeply in a good solvent than in a poor solvent and that this behavior was general and independent of grafting density. This behavior is counter to the notion that less interaction between a fluid (probe) and a solid surface promotes slip.

A holistic approach to natural ventilation studies

Natural ventilation in buildings can increase thermal comfort and reduce air-conditioning use. However, it is very challenging today to accurately determine the natural ventilation rate through a building. This paper outlines a method to calculate the wind distribution around a building site from information obtained at a meteorological station miles away. This paper also discusses the influence of surrounding buildings on the wind flow around a target building at the site, and presents various geometrical models. In addition, the use of hour-by-hour wind velocity typically available from a meteorological station may give rise to some errors because of the large time step. A correlation method can be employed to convert the hour-by-hour wind velocity to minute-by-minute velocity. One can then use CFD to calculate the airflow around the building and wind-driven cross ventilation through an apartment simultaneously. However, prediction of single-sided natural ventilation is difficult because of the bi-directional flow at the room opening and the complex flow around buildings. This paper presents an empirical model that can predict the mean and fluctuating ventilation rates due to the pulsating flow and eddy penetration of wind-driven single-sided ventilation in buildings with three types of windows. One must use the correct strategy in a building in order to achieve the maximum benefits of natural ventilation.

A holistic approach to natural ventilation studies

Natural ventilation in buildings can increase thermal comfort and reduce air-conditioning use. However, it is very challenging today to accurately determine the natural ventilation rate through a building. This paper outlines a method to calculate the wind distribution around a building site from information obtained at a meteorological station miles away. This paper also discusses the influence of surrounding buildings on the wind flow around a target building at the site, and presents various geometrical models. In addition, the use of hour-by-hour wind velocity typically available from a meteorological station may give rise to some errors because of the large time step. A correlation method can be employed to convert the hour-by-hour wind velocity to minute-by-minute velocity. One can then use CFD to calculate the airflow around the building and wind-driven cross ventilation through an apartment simultaneously. However, prediction of single-sided natural ventilation is difficult because of the bi-directional flow at the room opening and the complex flow around buildings. This paper presents an empirical model that can predict the mean and fluctuating ventilation rates due to the pulsating flow and eddy penetration of wind-driven single-sided ventilation in buildings with three types of windows. One must use the correct strategy in a building in order to achieve the maximum benefits of natural ventilation.

Experimental investigation of porous medium structural effects on a coupled porous media-free zone laminar flow

An experimental research program was conducted to investigate the effects of solid volume fraction, arrangement of rods, and rod shape on slow flow through and over two-dimensional model porous media. The porous media were modeled using in-line and staggered arrays of rods of circular and square cross-sections to cover a range of solid volume fraction of 0.06 to 0.49. Each model was installed into a test section so as to fill three-quarters of the total depth of the flow section; and the flow was driven through the test section by pressure. Using a refractive-index matched viscous fluid, the bulk Reynolds numbers for the respective test conditions were kept considerably lower than unity. Particle image velocimetry measurements were made across the streamwise-transverse plane of the test section. Results indicate that the flow through the free zone increases from 75% to nearly 100% as the solid volume fraction increases from 0.06 to 0.49. While the bulk distribution is independent of the shape of the rods, or the mode of arrangement, at the interface, penetration of the free flow is dependent on the solid volume fraction and arrangement of rods. The interfacial flow is predicted by a new formulation from which a boundary condition is derived which unlike others in the literature, is devoid of jumps at the interface. This work provides detailed experimental data and important predictive tools for validations of theoretical and numerical work.

Effect of Seagrass on Current Speed: Importance of Flexibility vs. Shoot Density

Water flow through seagrass beds transports nutrients, affects sediment stability and chemistry, and imposes hydrodynamic forces on shoots that alter canopy configuration. Past studies done under diverse conditions yielded conflicting results about the effects of shoot density on flow through seagrass bed canopies. We used eelgrass, Zostera marina, to study how the density of flexible shoots affect the hydrodynamics of seagrass beds (canopies) in unidirectional water flow. By exposing randomly-arranged shoots of uniform length to current velocities controlled in a flume, the effects of shoot density and downstream distance (position) could be determined without confounding factors. Comparison of velocity profiles within beds to those upstream of the beds showed that flow was slower in the beds. However, shoot density, position, and current velocity did not affect the percent reduction in flow velocity in a (sea)grass bed. Turbulence enhances mixing of substances carried in the water. Here, turbulence intensity (index of the importance of turbulent velocity fluctuations relative to average current velocity) was lower when ambient flow was faster, but was not affected by shoot density or position, Drag, the hydrodynamic force on a shoot that bends it over in the flow direction, provides another measure of how the canopy affects flow experienced by a shoot. Drag was not affected by current velocity, shoot density, or position in the bed. Gaps between shoots can enhance light and flow penetration into the canopy, but when shoots are bent over by flow, they can cover gaps. Faster ambient currents caused greater gap closure, which at each current speed was greater for high shoot densities. Thus, canopy gap closure did not correlate with percent flow reduction in grass beds or with drag on individual shoots, both of which were independent of shoot density and ambient current velocity. Since changing shoot density does not affect the flow in a grass bed exposed to a given ambient current, our results are inconsistent with the hypothesis that the high shoot densities observed in grass beds in habitats exposed to rapid flow are due to a direct, adaptive response of the grass to the flow environment.

Multi-Physics and CFD Analysis of an Enclosed Coaxial Carbon Nanotube Speaker for Automotive Exhaust Noise Cancellation

<div class="section abstract"><div class="htmlview paragraph">Automotive exhaust noise is one of the major sources of noise pollution and it is controlled by passive control system (mufflers) and active control system (loudspeakers and active control algorithm). Mufflers are heavy, bulky and large in size while loudspeakers have a working temperature limitation. Carbon nanotube (CNT) speakers generate sound due to the thermoacoustic effect. CNT speakers are also lightweight, flexible, have acoustic and light transparency as well as high operating temperature. These properties make them ideal to overcome the limitations of the current exhaust noise control systems. An enclosed, coaxial CNT speaker is designed for exhaust noise cancellation application. The development of a 3D multi-physics (coupling of electrical, thermal and acoustical domains) model, for the coaxial speaker is discussed in this paper. The model is used to simulate the sound pressure level, input power versus ambient temperature and efficiency. The 3D model provides accurate results of the temperature profile and heat flow as compared to a 2D model. Also, the flow of exhaust gases can be efficiently modeled using a 3D model. The flow analysis would help understand any flow penetration into the speaker as well as the effect of heat transfer due to the flow. The model is validated by comparing the experimental results with the simulation results. Along with multi-physics simulation, CFD analysis of the coaxial speaker is also studied in this paper. The CFD analysis is focused on the backpressure generated by the speaker and the flow path of the exhaust gases inside the CNT speaker.</div></div>

Distribution of phosphorus in bed sediment at confluences responding to hydrodynamics

Knowledge of the distribution of contaminants at channel confluences is critical for understanding their transport and dwelling at river networks where flow confluences constitute the key nodes. Flume experiments were conducted to study the distribution of phosphorus adsorption in surface sediment under complex hydrodynamics at channel confluences. The influence of the discharge ratio of the tributary discharge to the main stream discharge was also investigated. The results showed that the horizontal velocity and vertical velocity of flow are the dominant factors affecting the distribution of phosphorus adsorption. Flows with a larger horizontal velocity are not beneficial to phosphorus adsorption on sediment and thus low- and high-adsorption strips of phosphorus occur in the maximum velocity zone and the flow separation zone, respectively. Downwelling flows are beneficial to phosphorus adsorption on sediment as they can enhance phosphorus exchange between overlying water and the bed sediment. A small flow penetration with a small discharge ratio causes a decrease in vertical velocity in the separation zone as well as the strong intrusion of a helical cell into the bottom of this zone, which results in an increase in horizontal velocity near the bed and consequently the phosphorus adsorption is largely restricted.

Purge flow effects on rotor hub endwall heat transfer with extended endwall contouring into the disk cavity

Efficiency improvements for gas turbines are strongly coupled with increasing turbine inlet temperatures. This imposes new challenges for designers for efficient and adequate cooling of turbine components. Modern gas turbines inject bleed air from the compressor into the stator/rotor rim seal cavity to prevent hot gas ingestion from the main flow, while cooling the rotor disk. The purge flow interacts with the main flow field and static pressure field imposed by the turbine blades. This complex interaction causes non-uniform and jet-like penetration of the purge flow into the main flow field, hence affecting the endwall heat transfer on the rotor. To improve the understanding of purge flow effects on rotor hub endwall heat transfer, an unshrouded, high-pressure representative turbine design with 3D blading and extended endwall contouring of the rotor into the cavity seal was tested. The measurements were conducted in the 1.5-stage axial turbine facility LISA at ETH Zurich, where a state-of-the-art measurement setup with a high-speed infrared camera and thermally managed rotor insert was used to perform high-resolution heat transfer measurements on the rotor. Three different purge flow rates were investigated with regard to hub endwall heat transfer. Additionally, steady-state computational fluid dynamics simulations were performed to complement the experiments. It was found that the local heat transfer rate changes up to ±20% depending on the purge flow rate. The main part of the purged air is ejected at the endwall trough location and swept towards the rotor suction side, which is caused by the interaction of main flow and the cavity extended endwall design. The presence of low momentum purge flow locally reduces the heat transfer rate. Changes in adiabatic wall temperature and heat transfer (depending on purge rate) are observed from the platform start up to the cross passage migration of the secondary flow structures.

Spudcan Penetration Simulation Using the Coupled Eulerian-Lagrangian Method with Thermo-Mechanical Coupled Analysis

A novel modeling technique based on the coupled Eulerian-Lagrangian (CEL) method is provided to solve the geotechnical problems with large deformations. The technique is intended to solve the update problem of soil mechanical properties during spudcan penetration in normally consolidated clay soil. In the CEL model, the normal method of assigning an increasing shear strength profile with depth (NA) is defective due to its Eulerian framework. In this paper, a new technique is proposed to update soil material properties by introducing thermo-mechanical coupled analysis (TMCA) to the CEL models. During establishment of the CEL models, the optimal penetration velocity and minimum mesh size are determined through parametric studies. Reasonability and accuracy are then verified through comparison of the preliminary results with the soil flow configuration and penetration resistance (Fv) of a centrifuge test, and the results of the proposed method are compared with those of the remeshing and interpolation technique with small strain (RITSS) method. To achieve a CEL model with satisfactory accuracy, the NA and TMCA methods implemented in the CEL models and the RITSS method are first adopted in weightless soil. Comparison of the findings with those obtained in previous studies shows that the TMCA method can update material properties and predict Fv. The TMCA method is then applied to soils with self-weight and different shear strength profiles. Results show that the proposed method is capable of accurately modeling the large deformation problem of spudcan penetration in non-homogeneous clay.

A parametric study of angular road patterns on pedestrian ventilation in high-density urban areas

Road patterns are highly related to urban ventilation, which plays an important role for improving thermal comfort at the tropics. However, the effects of road intersection angles on the pedestrian-level wind environment remain uncertain. This study investigates the effects of angular road patterns in high-density urban areas using experimental and numerical methods. The studied road patterns are developed from four types of four-way road intersections with various road intersection angles from 90° to 45°. A reduced-scale angular road pattern was first tested in a wind tunnel experiment for validation purposes. The experiment indicates that the Reynolds-averaged Navier-Stokes (RANS) method (κ-ε model) is appropriate to solve the flow in the angular road network. The conducted numerical parametric study suggests the flow field is affected by both the prevailing wind direction and the relative orientation of adjacent road segments (i.e. stream-wise versus lateral; and upstream versus downstream). Based on the results, recommendations are provided for orienting the segments in regular and irregular road networks. In general, upstream road segments should be closely oriented to the wind direction to maximize the overall incoming flow, while moderate inflow angles should be designed for downstream road segments to balance the downstream and lateral flow penetration. These design recommendations of road networks provide the possibility to improve the pedestrian-level wind comfort by optimizing the flow distribution without sacrificing the limited land resources in tropical compact districts.