Blockage Ratio Research Articles

Numerical Investigation of Aerodynamic Characteristics of Hyperloop System Using Optimized Capsule Design

As a consequence of research on developing a speedy transportation system, Hyperloop is one of the best solutions now as smaller resistant forces are developed on the capsule body compared to conventional ground transportation systems due to movement in a vacuum and no contact with the ground. In this study, a capsule of an elliptical-shaped head and semicircular-shaped rear was chosen for analysis. Aerodynamic drags were calculated at different evacuated tunnel pressures. The computational regime was a 360 meters long tunnel. The inlet and outlet were pressure far-field boundaries while the wall was moving, with a Blockage Ratio (BR) of 0.36. Characteristics of different regions were identified in choked conditions. The drag was found to be lesser than the capsule of semicircular ends at different speeds. The pressure drag and friction drag were increased with the increase in velocity in the same tunnel pressure. By investigating different flow regions, it was found that a series of rhomboidal-shaped shock waves appear at high speeds. The formation and nature of this shock wave were also investigated, and found that it is caused due to shock wave and expansion wave interaction that results in the fall of pressure and temperature in the wake region.

Experimental and multiphase modeling of small vertical-axis hydrokinetic turbine with free-surface variations

Vertical-axis hydrokinetic turbines are promising option to harness the low velocity currents. However, limited investigations have been carried out considering the interactions between the turbine rotor and the channel section, including the free-surface. Thus, a vertical-axis turbine model has been designed and manufactured, to be tested in an open channel. Also, a three-dimensional multiphase simulation has been carried out, using the volume of fluid (VOF) model, to capture the air–water interface and to investigate the free-surface variations effects on the turbine output. Experimentally, the turbine model has been characterized under different flow conditions and free-surface levels. The peak power coefficients are found to increase with the upstream velocity. This effect is directly linked to the blockage ratio and the Froude number. A reasonably good match has been found between the experimental and the numerical results. The VOF model is able to simulate the free-surface longitudinal variations, and the effect of the turbine blockage of the channel. The velocity field and the pressure coefficient distribution, around the turbine rotor, have been studied and correlated with the free-surface variations from upstream to downstream of the turbine. Finally, the vortex street generated by the blade–plate interaction has been analyzed.

Influence of the canal width and depth on the resistance of 750 DWT Perintis ship using CFD simulation

Investigation of hydrodynamic interaction between the vessel and the seabed when entering shallow water is considered one of the most critical considerations of inland waterway transport. There are many investigations into the behavior of ships in restricted waters, such as ships traveling in different forms of canal cross-sections. The present study aims to evaluate the hydrodynamic interaction of the 750 DWT Perintis Ship moving through the different canal types to determine the relative effects of limiting the width and depth cross section on the ship's resistance. Two different canals with different cross sections, including canal bank and rectangular canal, were evaluated to investigate the influence of canal width (Wb), depth ratio (hw/T), and blockage ratio function (As/Ac). The Computational Fluid Dynamic (CFD) method with Reynolds-averaged Navier–Stokes (RANS) solver and turbulent model 𝑘−𝜀 were used to predict the total resistance of the ship. The proposed numerical simulation was initially validated with an experimental towing tank test in the error range of 0.11-7.74%. The results indicated similar phenomena were found both in rectangular and canal banks. The case with a shallower (lower hw/T) and a narrower (lower Bc/Bs) canal dimension has a higher resistance value. Backflow and subsidence of free surface became significant around the ship's hull in more restricted water, changing the ship's hydrodynamic characteristics and increasing resistance. It can be found that the higher the blockage ratio (mb), the higher the total resistance value in both canal types, which proved that ships with higher speeds were more sensitive to changes in waterway restrictions.

Investigation on favorable pressure gradient in an atmospheric boundary layer wind tunnel using large‐eddy simulation and its impact on wind field and surface pressure measurement

AbstractA constant cross‐section wind tunnel usually experiences a negative pressure gradient (ie, favorable pressure gradient, FPG), resulting in a certain degree of discrepancy between the simulated and idealized atmospheric boundary layer (ABL) flows. To investigate its impact, three large‐eddy simulation (LES) cases were conducted in this study: one simply reproduced a wind tunnel, one removed the FPG by adjusting the ceiling height, and one reduced the FPG by canceling unnecessary boundary layers associated with the tunnel sidewalls and ceiling. The required ceiling height in the second case was estimated based on the pressure gradient in the first case. The FPG was found mainly generated by the contraction effect induced by the boundary layers over the tunnel walls because it can be largely removed in the third case. In addition, we investigated the mean and standard deviation of the surrounding wind field and surface pressure coefficient of an isolated square‐section building model. Because the FPG in the macroscale ABL is negligible compared with the adverse pressure gradient in the microscale near‐wall boundary layers of the building, the influence of the FPG is negligible in a wind tunnel experiment conducted in a relatively large wind tunnel with a safe blockage ratio.

Investigating the Effects of Blockage Ratio on the Performance of a Surface-piercing Propeller in Free Surface Water Tunnel Tests

This paper investigates the effect of the immersion ratio parameter on the hydrodynamic performance of three surface-piercing propellers with diameters of 0.125, 0.132 and 0.140m at different advancing speeds. Experimental tests have been carried out in the free surface water tunnel of the Babol Noshirvani University of Technology. The results showed that the maximum thrust coefficient of three propellers occurs in the velocity range of 3-3.5 m/s. This interval represents the transition area of the three propellers. Also, the effect of the blockage ratio on the hydrodynamic coefficients of three propellers relative to the advance coefficient has been studied. By increasing the immersion depth raises the propeller's wet surface and increases the thrust and torque hydrodynamic coefficients. However, growing the propeller's diameter to 0.140m causes the effect of the blockage ratio parameter by increasing the immersion and the propeller's torque experiences a decreasing trend. Therefore, maximum propeller efficiency value with diameter 0.140m in immersion ratio 0.60 and 0.70, incresing 38% and 44%, respectively; relative to other proepllers. Also, the curve of the efficiency gradient of three propellers in the optimum immersion ratio of 0.40 compared to the advancing coefficient shows that the maximum efficiency gradient occurs in the range of 0.7 to 0.9.

A PIV study of blockage ratio effects on flow over a confined circular cylinder at low Reynolds numbers

A PIV study of blockage ratio effects on flow over a confined circular cylinder at low Reynolds numbers

Nipple fluid for breast cancer diagnosis using the nanopore of Phi29 DNA-packaging motor

Detection of cancer in its early stage is a challenging task for oncologists. Inflammatory breast cancer has symptoms that are similar to mastitis and can be mistaken for microbial infection. Currently, the differential diagnosis between mastitis and Inflammatory breast cancer via nipple aspirate fluid (NAF) is difficult. Here, we report a label-free and amplification-free detection platform using an engineered nanopore of the phi29 DNA-packaging motor with biomarker Galectin3 (GAL3), Thomsen-Friedenreich (TF) binding peptide as the probe fused at its C-terminus. The binding of the biomarker in NAF samples from breast cancer patients to the probe results in the connector's conformational change with a current blockage of 32 %. Utilization of dwell time, blockage ratio, and peak signature enable us to detect basal levels of biomarkers from patient NAF samples at the single-molecule level. This platform will allow for breast cancers to be resolved at an early stage with accuracy and thoroughness.

Viscoelastic Capillary Flow Cytometry

A compact microfluidic flow cytometer is demonstrated, comprising viscoelastic flow focusing in fused silica capillaries and a fiber optical interface. Viscoelastic flow focusing enables simple device design and operation with a single‐inlet/outlet fluidic configuration. Fused silica capillaries with different inner diameters are effortlessly interchanged to eliminate blockage ratio limitations and enable single‐train particle focusing for a wide range of particle sizes and geometries. The compact system is mounted on an inverted microscope for easy integration with optical imaging and other optofluidic modalities, such as optical trapping and particle sorting. A real‐time cytometric analysis of three channels, forward scattering, side scattering, and fluorescence detection, is performed on LABVIEW. A throughput of 3500 events s−1 is performed on particles of sizes ranging from 2 to 20 μm, using capillaries of different inner diameters ranging from 30 to 75 μm. The outer diameter of all capillaries is identical to the cladding diameter of the applied optical fibers. This enables easy exchange and precise optical alignment of fibers and capillaries on a microfabricated jig. The performance of the microfluidic flow cytometer is benchmarked using polystyrene calibration beads, poly(lactic‐co‐glycolic acid) particles, erythrocytes, THP‐1 leukemic monocytes, and human metaphase chromosomes.

Experimental study on local droplet parameters in a deformed 2 × 2 Rod bundle under air-water annular-mist flow

During reflood conditions following a loss-of-coolant accident in pressurized water reactors, droplet flow affects the heat and mass transfer between liquid and steam phases. Flow behavior is further complicated by fuel rod cladding deformation. Accurate knowledge of the large interfacial area liquid droplets characteristics and the effect of rod deformation is essential for understanding the associated thermal-hydraulic process and guaranteeing nuclear safety. This study aims to investigate the effect of fuel rod deformation on the characteristics and distribution of local droplet parameters. Experiments were conducted in a vertical 2 × 2 deformed rod bundle with two deformed test sections with blockage ratios of 25% and 50%. Tests were performed under annular-mist flow conditions at atmospheric pressure over superficial liquid and gas velocities ranges of 0.020–0.040 m/s and 25–35 m/s, respectively. A double-sensor optical fiber probe was used to measure local droplet parameters downstream of the deformed region on the measuring planes. For a quantitative characterization of the effect of rod deformation on local droplet parameter distribution, the results of the deformed bundle tests were compared with those of the previous intact bundle tests. Furthermore, a prediction correlation for the bundle deformation-enhanced droplet mass flux ratio was proposed. The results of this study provide a better understanding of the complex reflood flow behavior and improve the predictability of numerical simulations.

Thermal effects on the wall surfaces of transonic evacuated tube maglev transportation

Shock waves and expansion fan hierarchies in complex flows induced by transonic evacuated tube maglev transportation (ETMT) cause a unique thermal environment, which can increase the aerodynamic heating on the wall surfaces of the train and tube with the possibility of structural damage. In this study, the thermal effects on the wall surfaces of transonic ETMT were numerically investigated using a density-based computational fluid dynamics (CFD) solver. The results show different thermal effects for choked and unchoked flows in the tube. For the train, the extreme hot or cold environment, which is non-uniformly distributed on the surface, occurs more easily in the choked flow. For the tube, the instantaneous thermal impact is severe on the wall at supersonic speeds in the choked flow, reaching a maximum of 43.2 kW/m2 at Mach 1.5 with a blockage ratio of 0.2. The spectrum of the heat flux fluctuation on the tube wall is divided into the low-frequency band (main frequency) subjected to the normal or bow shock wave and secondary-frequency band induced by the downstream reflected shock trains. In addition, the amount of heat accumulated on the tube is insignificant owing to the interaction between the expansion fans and shock waves with alternating action on the boundary layer. Adoption of these findings, including the thermal control techniques and thermal-impact-resistant materials, for different ETMT systems can promote high-efficiency and low-redundancy designs of thermal protection systems.

Prediction of Slip Velocity at the Interface of Open-Cell Metal Foam Using 3D Printed Foams

An open-cell metal foam gains a lot of interest from researchers due to its unique porous structure, which provides high surface area and good tortuosity, as well as being lightweight. However, the same structure also induces a massive pressure drop which requires an optimum design to suit applications, for example, a partially filled setup or staggered design. Thus, better attention to the slip velocity at the interface between the porous structure and non-porous region is required to maximize its potential, especially in thermal fluid applications. This study proposed a slip velocity model of an open-cell metal foam by using a reverse engineering method and 3D printing technology. A series of experiments and a dimensionless analysis using the Buckingham-Pi theorem were used to compute the slip velocity model. Results show that the pressure drop increases with decreasing pore size. However, the blockage ratio effects would be more significant on the pressure drop with foams of smaller pore sizes. The proposed slip velocity model for an open-cell metal foam agrees with the experimental data, where the predicted values fall within measurement uncertainty.

Influence of change in obstacle blocking rate gradient on LPG explosion behavior

The aim of this study was to examine the propagation characteristics of liquified petroleum gas (LPG)/air explosion. As such, the flame propagation process and pressure parameters of LPG explosion with an equivalent ratio of 1 were obtained using horizontal, long straight pipes and a high-speed camera. The large eddy simulation and power-law flame model were used to reproduce the simulation results, and the morphological evolution of the flame front during the explosion process was analyzed. The results showed that as the blockage ratio gradient increased, the time required for the flame to propagate from the electrode to the end of the pipe increased. Meanwhile, a flocculent flame formed at the end of the pipeline with a blockage ratio of 91%. Additionally, the maximum flame propagation speed changed in the same way as the blockage ratio. The gradient change of the barrier blockage ratio considerably influenced the pressure kinetics characteristics of LPG explosion: the maximum explosion pressure increased first and then decreased, the time to reach the maximum explosion pressure increased, and the deflagration index increased first and then decreased. The chemical kinetics analysis of premixed gas showed that when propane, n-butane, and isobutane were present in the premixed system, some of the elemental reactions that promote n-butane consumption inhibited propane and isobutane consumption. Meanwhile, the formation and consumption rate of H*, O*, and OH* from LPG during the explosion process was less than that of single-component combustible gas except propane.

Effects of Hole Blockage on Endwall Film Cooling and Vane Phantom Cooling Performances of a Transonic Turbine Vane

Abstract Although the thermal-barrier coating (TBC) can protect the gas turbine components from the hot mainstream gas, it is not uncommon that the TBC partially blocks the film cooling holes during the spraying process. The film cooling hole blockage will alter the coolant flow behaviors and lead to a significant variation in film cooling performance. In this paper, a physical model of blockage holes including two key parameters of blockage ratios (B) and blockage angles (α), was proposed to analyze the effects of hole blockage on endwall film cooling performance, phantom cooling performance of vane pressure side surface (PS), and overall cooling performance. Based on a proposed double-coolant-temperature prediction method, the endwall film cooling effectiveness, phantom cooling effectiveness of the vane PS and area-averaged cooling effectiveness of an actual vane passage were numerically calculated and analyzed, for the common holes and blockage holes (three different blockage ratios of B and three different blockage angles of α) at the similarly realistic operating conditions of a gas turbine. Results indicated the hole blockage is pernicious to endwall film cooling performance, leading to a significant decrement of endwall film cooling effectiveness (up to 30% at B = 0.4), where the decrement magnitudes increase with increasing the blockage ratios (B). Compared to the blockage ratios (B), the effects of blockage angle (α) on endwall film cooling effectiveness are secondary and slight (less than 10% in η). Nonetheless, the hole blockage is beneficial to phantom cooling performance of the vane PS, leading to an obvious enhancement (more than 40%) in area-averaged phantom cooling effectiveness with increasing blockage ratios (B), due to the increase of the local blowing ratio (BReff). The area-averaged cooling effectiveness including endwall film cooling and phantom cooling on PS, decreases with the increase of blockage angle (α), and the benefits of hole blockage in overall cooling performance are negative at α = 20 deg. This suggests that the overlarge blockage ratios and short blockage lengths (correspond to the blockage position near film cooling holes exit or large blockage angle of α), should be utmost avoided during the spraying process of the TBC, otherwise, the film cooling scheme designs, based on the geometry of the pristine holes, may be inefficient.

Backwater assessment for the energy conversion through hydrokinetic turbines in subcritical prismatic canals

Hydrokinetic turbines exploit partially the total head variation created in natural and artificial waterways. In subcritical flows, the sum of the energy harvested mechanically and the energy dissipated by fluid-dynamic losses and viscous friction is balanced through a backwater extending far upstream. The latter depends on the turbine operating condition and, thus, on the thrust force generated.Only the downstream momentum is known, whilst upstream momentum and turbine thrust force are undetermined. To solve this problem, a method is developed to update the inflow factor for a single turbine, thus achieving a single physical solution. Froude number and blockage ratio are updated at each iteration and are used as independent variables for solving the turbine model. According to the actual canal geometry, a specific continuity equation allows to infer the backwater depth from the inflow factor. Hence, this method can be integrated with confined BEM and DMS models to extend the capability of the simulation tool.Experimental data of inflow depth are used to validate this model for single rotors in a subcritical environment, whilst its extension allows the assessment of turbine arrays in artificial canals exploited for hydropower purposes.

Study on the influence of flow blockage in severe accident scenario of CAP1400 reactor

Deformed fuel rods can cause a partial blockage of the flow area in a subchannel. Such flow blockage will influence the core coolant flow and further the core heat transfer during the reflooding phase and subsequent severe accidents. Nevertheless, most of the system analysis codes simulate the accident process based on the assumed flow blockage ratio, resulting in inconsistencies between simulated results and actual conditions. This paper aims to study the influence of flow blockage in severe accident scenario of the CAP1400 reactor. First, the flow blockage model of ISAA code is improved based on the FRTMB module. Then, the ISAA-FRTMB coupling system is adopted to model and calculate the QUENCH-LOCA-0 experiment. The correctness and validity of the flow blockage model are verified by comparing the peak cladding temperature. Finally, the DVI Line-SBLOCA accident is induced to analyze the influence of flow blockage on subsequent CAP1400 reactor core heat transfer and core degradation. From the results of the DVI Line-SBLOCA accident analysis, it can be concluded that the blockage ratio is in the range of 40%–60%, and the position of severe blockage is the same as that of cladding rupture. The blockage reduces the circulation area of the core coolant, which in turn impacts the heat exchange between the core and the coolant, leading to the early failure and collapse of some core assemblies and accelerating the core degradation process.

Three-dimensional numerical investigation on flow behaviors around a diversion dike

Three-dimensional numerical simulations of a flow past a non-submerged diversion dike are performed for various blockage ratios (1/6 ≤ β ≤ 1/3) and Froude numbers (0.152 ≤ Fr ≤ 0.253). The instantaneous and time-averaged flow characteristics, the evolution process of mixing layers, and the bed shear stress of the dike are analyzed. The blockage ratio β plays an important role in the momentum redistribution and turbulent kinetic energy of the diversion dike. As the blockage ratio increases, the flow velocity gradient and the vortex shedding frequency in the mixing layer significantly increase. The Froude number Fr has little effect on the flow field. A large recirculation zone is observed in the wake of the dike, and the recirculation length is more depended on the length of the dike rather than the Froude number. The bed shear stress around the dike increases significantly with the increase in the blockage ratio.

Dynamics of a collapsible tube with internal constriction

The deformation and oscillation dynamics of a thin-walled collapsible tube carrying internal flow with and without internal constriction is studied experimentally and theoretically for a constant chamber pressure. The internal constriction of different blockage ratios is employed by attaching spherical balls of different diameters to the inner wall of the tube. The effect of the axial location of the constriction is also studied. Without any internal constriction, the tube response is observed to be steady collapsed, periodic/aperiodic oscillatory or steady distended, depending on the Reynolds number. With constriction of low blockage ratios near the inlet of the collapsible tube, the system exhibits oscillatory response; however, no aperiodic oscillations are found. With bigger constrictions, the oscillations are completely suppressed. The viscous pressure drop due to the constriction is responsible for this behavior. When the constriction is present at the middle of the tube, the downstream half of the tube is under high tension, leading to the excitation of first and second radial vibrational modes of the tube (which are different from the milking-mode oscillations), depending upon the Reynolds number and blockage ratio. The results from a lumped parameter-based theoretical model are able to capture most of the qualitative features of the tube response such as the shift of the Hopf bifurcation point and the shrinkage of the oscillatory regime.

Experimental and Simulation Investigation of Performance of Scaled Model for a Rotor of a Savonius Wind Turbine

Renewable energy sources are preferred for many power generation applications. Energy from the wind is one of the fastest-expanding kinds of sustainable energy, and it is essential in preventing potential energy issues in the foreseeable future. One pertinent issue is the many geometrical alterations that the scientific community has suggested to enhance rotor performance features. Hence, to address the challenge of developing a model that resolves these problems, the purpose of this investigation was to determine how well a scaled-down version of a Savonius turbine performed in terms of power output using a wind tunnel. Subsequently, the effect of the blockage ratio produced in the wind tunnel during the chamber test on the scaled model was evaluated. This study discusses the influences of various modified configurations on the turbine blades’ torque and power coefficients (Cp) at various tip speed ratios (TSRs) using three-dimensional (3D) unsteady computational fluid dynamics. The findings showed that the scaled model successfully achieved tunnel blockage corrections, and the experimental results obtained can be used in order to estimate how the same turbine would perform in real conditions. Furthermore, numerically, the new models achieved improvements in Cp of 19.5%, 16.8%, and 12.2%, respectively, for the flow-guiding channel (FGC at Ⴔ = 30°), wavy area at tip and end (WTE), and wavy area on the convex blade (WCB) models in comparison to the benchmark S-ORM model and under identical wind speed conditions. This investigation can provide guidance for improvements of the aerodynamic characteristics of Savonius wind turbines.

Hollow bluff body-stabilized natural gas-air premixed flames

The effects of hollow bluff body geometry, surface curvature, blockage ratio, mixture residence time, impingement strength, heat recirculation eddy size, Reynolds and Froude numbers were all investigated via 10 bluff body shapes. It was found that duplicating the wake flow zone and increasing the mixture flow velocity inside the bluff body cavity via a disc configuration provide a maximum blow-off velocity of 49 m/s. Enlarging the bluff body exterior surface area and the flow wake width in addition to elongating the mixture residence time inside the bluff body cavity via a trapezoidal configuration yield a minimum lean limit of 0.42. Having grooves on the bluff body exterior surface or providing a concave surface part at the wake region favorably develops flow turbulence and intensive heat recirculation. The bluff body cavity height should be adjusted at an optimum value which keeps a high impingement velocity onto the combustor hot surface via a large vortex and simultaneously allows enough mixture preheating length. The stability limits were thus correlated to the geometrical and thermal effective parameters in addition to Reynolds and Froude numbers.

Numerical Simulation of the Influence of Hydrogen Concentration on Detonation Diffraction Mechanism

In this study, the impact of hydrogen concentration on deflagration to detonation transition (DDT) and detonation diffraction mechanisms was investigated. The combustion chamber was an ENACCEF facility, with nine obstacles at a blockage ratio of 0.63 and three mixtures with hydrogen concentrations of 13%, 20%, and 30%. Detonation diffraction mechanisms were numerically investigated by a density-based solver of OpenFOAM CFD toolbox named ddtFoam. In this simulation, for the low Mach numbers, the pddtFoam solver was applied, and for high speeds, the pddtFoam solver switched to the ddtFoam solver to simulate flame propagation without resolving all microscopic details in the flow in the CFD grid, and to provide a basis for simulating flame acceleration (FA) and the onset of detonation in large three-dimensional geometries. The results showed that, for the lean H2–air mixture with 13% hydrogen concentration, intense interaction between propagating flame and turbulent flow led to a rapid transition from slow to fast deflagration. However, the onset of detonation did not occur inside the tube. For the H2–air mixture with 20% hydrogen concentration, the detonation initiation appeared in the acceleration tube. It was also found that following the diffraction of detonation, the collision of transverse waves with the wall of the tube and the reflection of transverse waves were the most essential and effective parameters in the re-initiation of the detonation. For the H2–air mixture with 30% hydrogen concentration, the detonation initiation occurred while passing through the obstacles. Subsequently, at detonation diffraction, the direct initiation mechanism was observed.