Time-averaged Pressure Research Articles

The effect of transverse inclination angle on hydrodynamic characteristics of two tandem circular cylinders in an X arrangement

A numerical investigation of the flow around two stationary circular cylinders in an X arrangement, with a Reynolds number of Re = 3900 and a spacing ratio of L/D = 4.0, is conducted using Large-Eddy Simulation. Eight different transverse inclination angles (α = 0°–30°) are considered to investigate their effects on several aspects, including the time-averaged drag coefficient (Cd-ave), root-mean-square lift coefficient (Cl-rms), Strouhal number (St), instantaneous flow structure, and time-averaged pressure distribution. The numerical results demonstrate that when the inclination angle exceeds a critical value of αc = 12.5°–15°, the flow pattern in the gap between two cylinders transitions from the reattachment regime to the co-shedding regime. This flow transition indicates that the wake vortex periodically detaches from the upstream cylinder and impinges on the downstream cylinder, resulting in a sharp increase in force coefficients, especially for the downstream one. When compared with α = 15°–30°, the force coefficients for both cylinders at α = 0°–12.5° are reduced, which is favorable to the structural stability. Furthermore, an increase in α leads to a monotonic rise in Cd-ave for the downstream cylinder. This can be primarily attributed to the amplified pressure coefficient on the front face of the downstream cylinder, which is caused by the reduced shielding effect from the upstream one.

Biomechanical performance of the Bicaval Transcatheter System for the treatment of severe tricuspid regurgitation.

Introduction: Tricuspid regurgitation (TR) is a relatively common valvular disease, which can result from structural abnormalities of any anatomic part of the tricuspid valve. Severe TR is linked to congestive heart failure and hemodynamic impairment, resulting in high mortality when repaired by elective surgery. This study was undertaken to quantify the structural and hemodynamic performance of the novel Transcatheter Bicaval Valves System (TricValve) percutaneously implanted in the superior vena cava (SVC) and inferior vena cava (IVC) of two patients with severe TR and venous congestion. Methods: After developing the SVC and IVC device models, the contact pressure exerted on the vena cava wall was obtained by computational analysis. Both smoothed-particle hydrodynamics (SPH) and computational fluid dynamics were carried out to quantify caval reflux in the right atrium and the pressure field of pre- and post-TricValve scenarios, respectively. Results: Analysis of contact pressure highlighted the main anchoring area of the SVC device occurring near the SVC device belly, while the IVC device exerted pronounced forces in the device's proximal and distal parts. SPH-related flow velocities revealed the absence of caval reflux, and a decrease in time-averaged pressure was observed near the SVC and IVC after TricValve implantation. Discussion: Findings demonstrated the potential of computational tools for enhancing our understanding of the biomechanical performance of structural tricuspid valve interventions and improving the way we design next-generation transcatheter therapies to treat the tricuspid valve with heterotopic caval valve implantation.

Investigation on the fluid-solid coupling effect in high-speed train’s windshield structure

The high-speed train’s windshield structure is vital to the boundary layer development and drag reduction design. Up to date, windshield structures are assumed as rigid body in most train aerodynamic numerical simulations. This research investigates the fluid-solid coupling effect of high-speed train’s windshield structure based on an 8-car formation model. The influence of speed level and windshield installation location on the flow field parameter and windshield deformation profile are systematically analysed. The results indicate that, with the development the boundary layer, the time-averaged pressure coefficient, lateral force coefficient and windshield’s displacement all gradually decrease from 1st windshield to 4th windshield along the stream direction. In the connecting region between the windshield and vestibule, a pair of negative pressure zone are formed and gradually intensify along the downstream direction, such that the time-averaged deformation, as well as the vibration amplitude of windshields experience a slight increase. According to the power spectral density analysis, the vibration frequency of all windshields’ displacement varies between 10.25 Hz and 12.5 Hz. Meanwhile, the pantograph structure will lead to the generation of vortex group, these vortices will lead to additional small low frequency peaks for windshields installed on the downstream direction of pantograph.

Droplet Evolution from a Single Hydrophobic Pore in the Diffusion Media of Polymer Electrolyte Fuel Cells: A Conceptual Analysis

Maintaining a well-balanced water distribution is crucial for the operation of polymer electrolyte fuel cells. The water distribution depends to a large extent on the ease of liquid water transport in the diffusion media (DM) and in the flow field (FF) on the cathode side and, especially, on processes in boundary regions between these media. In this article, the droplet dynamics at the DM-FF interface are studied by a mechano-hydrodynamic pore model. The presented treatment allows droplet detachment to be rationalized, in dependence of pore radius and air flow velocity. Large pore radius and high air flow velocity favor droplet detachment during an earlier stage of growth, at which the contact line of the droplet remains pinned at the pore opening while the droplet volume expands during growth. We evaluate the trend of detachment time and detachment height of a droplet. Furthermore, we analyze the influence of the air flow velocity on the time-averaged liquid pressure at the pore exit. The physics governing the flooding behavior of the pore is discussed. The presented model-based analyses provide theoretical insights into material properties and operating conditions that improve water removal.

Lattice Boltzmann method for heat transfer in transitional flows with unified single-node curved boundary conditions

Laminar separation bubbles in transitional flows of low-Reynolds-number airfoils significantly affect aerodynamic efficiency and heat transfer characteristics, which can be dealt with using the numerical method with boundary treatment of complex geometry. This work proposes the unified single-node curved boundary conditions based on the thermal lattice Boltzmann method, and several benchmarks verify the higher accuracy and parallel scalability over conventional schemes. Multi-GPU simulations for airfoil Eppler 61 and SD8020 are carried out, and the lift coefficients CL are accurately simulated by the parametric combined momentum-exchange method. Furthermore, time-averaged pressure coefficients Cp and local Nussel number Nu of airfoil surfaces are obtained, and the unsteady flow and heat transfer characteristics of laminar separation bubbles are captured. Simulated average Nussel numbers Nu¯ for an Eppler 61 airfoil with different Reynold numbers are equivalent to and modify the Hilpert correlation. The numerical method can quickly and accurately predict transitional flows of low-Reynolds-number airfoils and guide the design and application of heat transfer with blade configuration.

Flow over a forward-facing step with a flexible membrane at its leading edge

The effects of a flapping membrane at the leading edge of a forward-facing step (FFS) on the flow over and pressure fluctuation on it were experimentally investigated. The FFS was immersed in the oncoming boundary layer (δ/h = 0.4, where δ and h are the oncoming boundary layer thickness and step height, respectively) and the Reynolds number, based on the step height and oncoming flow velocity (U∞) was 3.4×104. Both the length and width of the membrane were identical to h, the height of the FFS. Two-dimensional particle image velocimetry (PIV) and smoke-wire flow visualization techniques were used to investigate the flow over the FFS. Pressure scanners have also been used to study the pressure distribution on an FFS. It was found that the membrane flapped periodically under the effects of the separated shear flow from the leading edge of the FFS, which significantly suppressed the separation bubble on the FFS and prompts an early recovery of the time-averaged pressure. The phase-averaged results revealed that the flapping membrane generated alternating vortices over the FFS. These flapping-induced vortices (FIVs) enhance the Reynolds stresses over the FFS, increasing momentum transport in the wall-normal direction. Moreover, these FIVs synchronize with the pressure fluctuation on the FFS.

Numerical Analysis of Airfoil Flow Control Using a Nanosecond Pulsed Plasma Actuator

The control mechanism of a nanosecond dielectric barrier discharge (NS-DBD) actuator for suppressing laminar separation on airfoils was investigated using two-dimensional scale-adaptive simulations. To model the control effect of the NS-DBD actuator, a surface heating approach based on the analytical solution for transient one-dimensional heat conduction has been used. The focus of the investigation lies in the study of vortex formation and evolution induced by the actuator. A NACA 0015 profile was simulated at 14° with 250,000 chord-based Reynolds number. Regarding energy deposition, a low-energy case and a high-energy case were simulated. Several actuation parameters were varied, including the electrode position and surface temperature. In addition, the influence of constant and temperature-dependent modeling of the kinematic viscosity was investigated. The results for the time-averaged pressure coefficients show excellent agreement with measurement results. High grid resolution in the boundary layer allowed a detailed investigation of the vortex formation process. The main finding is that vortices are generated by baroclinic torque and vortex dilatation and not by a Kelvin–Helmholtz instability. Initially, tiny vortices form at the beginning of the separation region. Subsequently, these vortices are carried downstream and grow in size, thus preventing full separation due to momentum transfer from the external flow.

Impact of mixture mass flux on hydrodynamic blockage ratio and Mach number of rotating detonation combustor

To analyze non-ideal phenomena, such as burned gas backflow and non-detonation combustion, which affect the rotating detonation wave Mach number, simultaneous self-luminous visualization, time-averaged static pressure, fluctuating pressure, and thrust measurements with gaseous ethylene and oxygen were performed. Consequently, by doubling the number density of the fuel injectors, the hydrodynamic blockage ratio at the oxidizer inlet increased approximately 1.7-fold under the same oxidizer inlet area conditions. This may be attributed to the increase in the detonation propagation Mach number owing to the enhanced mixing of fuel and oxidizer. The relationship between the parasitic combustion fraction in front of the rotating detonation wave and the Mach number was also investigated by using a distributed heat release model. Consequently, it was suggested that experimental Mach number decreased from approximately 4.1 to 2.8 with increase in a mixture mass flux, and the theoretical detonation wave propagation Mach number was 7.3.

The new Kr-86 excess ice core proxy for synoptic activity: West Antarctic storminess possibly linked to Intertropical Convergence Zone (ITCZ) movement through the last deglaciation

Abstract. Here we present a newly developed ice core gas-phase proxy that directly samples a component of the large-scale atmospheric circulation: synoptic-scale pressure variability. Surface pressure changes weakly disrupt gravitational isotopic settling in the firn layer, which is recorded in krypton-86 excess (86Krxs). The 86Krxs may therefore reflect the time-averaged synoptic pressure variability over several years (site “storminess”), but it likely cannot record individual synoptic events as ice core gas samples typically average over several years. We validate 86Krxs using late Holocene ice samples from 11 Antarctic ice cores and 1 Greenland ice core that collectively represent a wide range of surface pressure variability in the modern climate. We find a strong spatial correlation (r=-0.94, p<0.01) between site average 86Krxs and time-averaged synoptic variability from reanalysis data. The main uncertainties in the analysis are the corrections for gas loss and thermal fractionation and the relatively large scatter in the data. Limited scientific understanding of the firn physics and potential biases of 86Krxs require caution in interpreting this proxy at present. We show that Antarctic 86Krxs appears to be linked to the position of the Southern Hemisphere eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability. We present a 86Krxs record covering the last 24 kyr from the West Antarctic Ice Sheet (WAIS) Divide ice core. Based on the empirical spatial correlation of synoptic activity and 86Krxs at various Antarctic sites, we interpret this record to show that West Antarctic synoptic activity is slightly below modern levels during the Last Glacial Maximum (LGM), increases during the Heinrich Stadial 1 and Younger Dryas North Atlantic cold periods, weakens abruptly at the Holocene onset, remains low during the early and mid-Holocene, and gradually increases to its modern value. The WAIS Divide 86Krxs record resembles records of monsoon intensity thought to reflect changes in the meridional position of the Intertropical Convergence Zone (ITCZ) on orbital and millennial timescales such that West Antarctic storminess is weaker when the ITCZ is displaced northward and stronger when it is displaced southward. We interpret variations in synoptic activity as reflecting movement of the South Pacific SPJ in parallel to the ITCZ migrations, which is the expected zonal mean response of the eddy-driven jet in models and proxy data. Past changes to Pacific climate and the El Niño–Southern Oscillation (ENSO) may amplify the signal of the SPJ migration. Our interpretation is broadly consistent with opal flux records from the Pacific Antarctic zone thought to reflect wind-driven upwelling. We emphasize that 86Krxs is a new proxy, and more work is called for to confirm, replicate, and better understand these results; until such time, our conclusions regarding past atmospheric dynamics remain speculative. Current scientific understanding of firn air transport and trapping is insufficient to explain all the observed variations in 86Krxs. A list of suggested future studies is provided.

Measurement of Inertial and Acoustic Waves in a Turbine Chute Rim Seal Cavity

AbstractA chute rim seal cavity has been instrumented with time-resolved and time-averaged pressure transducers as well as a gas concentration measurement system at the Oxford Rotor Facility. The unsteady pressure transducers were unevenly distributed along the circumference generating 15 combinations of angular spacing to conduct a phase analysis. The test operating conditions were modified through different configurations of mainstream flow, a range of rotational speeds and several rates of purge flow to obtain test data in the regimes of rotationally-driven, pressure-driven, and combined ingestion. The rotating unsteady flow structures within the rim seal cavity were studied through a combination of phase analysis of dynamic pressure signals and inspection of the frequency domain. The introduction of mainstream flow (axial and swirled) increased the overall unsteadiness exciting an additional band of lower frequencies. The phase analysis revealed these were associated with acoustic waves, providing the first experimental evidence of the presence and coexistence of inertial and acoustic waves in the rim seal cavity. The interaction of the inertial and acoustic waves strongly depends on the operating conditions, and may be linked to changes in sealing effectiveness.

Analysis of unsteady flow field and near-field aerodynamic noise of scale high-speed trains in long tunnel

The hybrid LES/APE method is used to simulate the unsteady flow field and the near-field aerodynamic noise of a 1/25 scale eight-coach high-speed train in long tunnel, validated by time-averaged pressure coefficients and Power Spectral Density of surface pressure from the aerodynamic wind tunnel test of a same scale two-coach train model. Train induced wind with the maximum velocity of 28 m/s in the opposite direction of train operating is formed in tunnel. Blocking effect leads to larger turbulent pressure and streamwise increment of turbulent power level from 133.7 dB to 138.2 dB, which is from130.3 dB to 133.4 dB in open air. With APE solver, three cases including tunnel with fully reflective walls, tunnel with fully absorptive walls and open air, are conducted to compare the influence of blocking effect and acoustic reflection on sound pressure. Total sound pressure level on the train body in tunnel is overall stronger than that in open air. The difference of sound power level between tunnel and open air is mostly contributed by acoustic reflection: 84.7 % at Coach 1, 84.3 % at Coach 8 and 66.0 ∼ 77.5 % from Coach 2 to Coach 7. Five peak frequencies: 520 Hz, 800 Hz, 1440 Hz, 2600 Hz and 3880 Hz are found from the frequency spectra of sound pressure of the probes in bogie cavities and pantograph grooves, in tunnel with fully reflective walls. Sound pressure modes help to clarify the generation mechanisms of peak frequencies: 520 Hz and 800 Hz are caused by the tunnel cavity resonance; 1440 Hz is caused by the first-order vertical mode from the bottom of the pantograph groove to the top of tunnel walls; 2600 Hz is caused by the first-order vertical mode from the ground to the top of bogie cavity, but 3880 Hz is not generated by simple in-phase cavity resonance.

Numerical investigation of a 1MW full-loop chemical looping combustion unit with dual CFB reactors

Chemical looping combustion (CLC) is a novel carbon capture technology with inherent advantage of CO2 separation and less energy penalty. The oxygen carrier circulates between the reactors realizing the transportation of oxygen and heat and preventing the mixing of air with flue gas. Currently, it lacks researches on the industrial scale system which operates autothermal. In this work, three-dimensional simulations of 1MW chemical looping combustion unit with gaseous fuel are presented in the frame of Eulerian approach. The configuration with dual circulating fluidized bed reactors is built according to the experimental construction, including air reactor, fuel reactor, loop seals, cyclones and L-valve. The time-averaged and local pressure, temperature and gaseous products are predicted numerically and compared with experimental measurements. Simulation results show that the reduction level changes by 0.08 between reactors corresponding to the oxygen transfer. Due to the exothermic process in air reactor, the difference of outlet temperature between air reactor and fuel reactor is 63 °C. Moreover, the higher operating temperature and solid inventory are beneficial for raising the performance of system. Results turn out that the numerical models developed in this work can be used for investigating detailed characteristic or scale-up of CLC system with high accuracy, high efficiency and low cost.

Particulate Deposition Effects on Internal Swirl Cooling of Turbine Blades

Abstract Particulate deposition effects on flow and heat transfer in an internal swirl tube subjected to fly ash ingestion were investigated by constructing an unsteady simulation framework, in which a particle–wall interaction model and a mesh morphing technique were implemented. Swirling flows in the swirl tube were induced by two tangential jet nozzles. Particles having a mean diameter of 6.5 μm were released from the nozzle inlets to model an exposure duration of 4500 h for engine operation in real fly ash environment using scale factors in the unsteady simulations. Particle deposition and its dynamic process were examined, and the effects of deposition on the swirling flow were quantified by comparing time-averaged velocity profiles, vorticity, pressure loss, and heat transfer with those from a clean tube without deposition. Results reveal that the most upstream section of the swirl tube captures the majority of the particles and the deposition distributions show a spiral pattern over the tube wall. The total mass of the deposits within the tube linearly increases, while local deposition thickness has a nonlinear relationship with the exposure time due to the interaction of the particles with the swirling flow. The deposition can generate a maximum of 15% reduction in cross-sectional area of the tube within the exposure duration, resulting in a reduced swirl number, because of the accelerated axial velocity and the decreased circumferential velocity, and further lower heat transfer in the downstream section of the tube relative to the clean tube case. However, as the heat transfer in the upstream deposition section is enhanced by the roughness due to the deposition, area-averaged heat transfer throughout the entire swirl tube is slightly improved by 4.0% but simultaneously a 179% higher pressure loss is observed, leading to an overall thermal performance value of 0.79 (relative to 1.0 for a clean tube), indicating substantial degradation of cooling performance in the fouled swirl tube.

Impact of pressure drop oscillations and parallel channel instabilities on microchannel flow boiling and critical heat flux

Microchannel flow boiling heat sinks that leverage the highly efficient heat transfer mechanisms associated with phase change are a primary candidate for cooling next-generation electronics in electric vehicles. In order to design flow boiling heat sinks for such practical applications, one key obstacle is an understanding of the conditions for occurrence of dynamic two-phase flow instabilities, to which microscale flow boiling is particularly susceptible, as well as their impact on heat transfer performance. While mapping the operational regimes of these instabilities has been well-studied, with numerous stability criteria available, their impact on the heat transfer performance of heat sinks in practical applications is not understood. This work seeks to assess the impact of pressure drop oscillations and parallel channel instabilities on the surface temperature and critical heat flux in parallel microchannel heat sinks. This is achieved through measurement of time-averaged steady-state temperatures and pressures, combined with high-frequency pressure signals and high-speed flow visualization. These data are compared across three controlled flow configurations that comprise a condition of stable flow boiling, a condition where only parallel channel instabilities can occur, and a third where both pressure drop oscillations and parallel channel instabilities can occur. Experiments are performed using the dielectric refrigerant HFE-7100 in 2 cm long parallel microchannel heat sinks with square-cross-section channels (0.25, 0.5, 0.75, and 1 mm widths) at three mass fluxes (100, 400, and 1600 kg/m2s). Across this range of conditions, the time-averaged surface temperature and critical heat flux were remarkably insensitive to the occurrence of these instabilities despite the significant hydrodynamic events and transient flow patterns observed.

Prediction of cavitation dynamics and cavitation erosion around a three-dimensional twisted hydrofoil with an LES method

The Large Eddy Simulation (LES) method coupled with a Schnerr and Sauer cavitation model was adopted to simulate the unsteady cavitating flow around a Delft Twist 11 (Twist11) hydrofoil. We proposed a novel aggressiveness indicator to predict the risk of cavitation erosion on the hydrofoil surface by utilizing LES simulations as input. The proposed aggressiveness indicator introduces the time-averaged pressure, the hypotheses of Nohmi et al. and the concept of the power exponent into the energy balance approach. The results show that the current numerical method integrally reproduces the evolution of the cloud cavity observed in the cavitation tunnel. The cavitation erosion risk predicted by the aggressiveness indicator ⟨e1⟩n=5′ agrees well with the erosion pattern obtained from the paint test. The predicted erosion risk regions are located in the “hoof” positions (region 2 and region 3) of the horse-shoe-shaped cloudy cavity and the positions (region 1) near the cavity closure line.

The effect of subbranch for the quantification of local hemodynamic environment in the coronary artery: a computed tomography angiography–based computational fluid dynamic analysis

Abstract Background Hemodynamic parameters derived from computed tomography angiography–based computational fluid dynamics (CFD) analysis have been widely used for clinical decision-making and researches to assess the vulnerability of atherosclerotic plaques and explain the initialization and development of atherosclerosis. Subbranches in the CFD model might affect the accuracy of hemodynamic parameters, but the effectiveness has been least quantified. Methods A coronary artery baseline model was generated with focal stenosis at the proximal left anterior descending artery. Nineteen comparing models were created by systematically removing various subbranches to examine the changes in hemodynamic parameters, including time-averaged pressure (TAP), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and particle relative residence time (RRT). Changes in these parameters were assessed quantitatively around the stenosis and near the region where subbranches were removed. Results The removal of subbranches caused a significant change in outflow rate, and there was generally a decrease in all CFD parameters in the regions of interest with a decrease in outflow rate. The subbranch removal had a significant impact on the calculation of TAWSS, OSI, and RRT, whereas TAP was insensitive to the removal with approximately 0.25% variation in all 19 models. The local effect from removing branch segments generally became negligible after 5 diameters away from the cutting-off position, but the decrease could be affected by other factors, such as a large curvature. Conclusion The outflow rate is a dominant factor for the calculation of TAP, TAWSS, OSI, and RRT. Removal of subbranches has a minor effect on the TAP calculation, but its effect is considerable on the TAWSS, OSI, and RRT. The effect of subbranch removal is limited in a region with 5 local diameters.

Aerodynamic influences of typical windbreak wall types on a high-speed train under crosswinds

The effect of windbreak wall types on their windproof effects on trains has been systematically investigated by comparing the flow field around a high-speed train behind three typical windbreak walls. These three typical windbreak walls are widely used along the windy railway lines in China, which include the earth embankment–type windbreak wall (EW), the road cutting–type windbreak wall (RW), and the straight reinforced concrete–type windbreak wall (SW). We compared the time-averaged crosswind-induced flows and aerodynamic performances of high-speed trains behind these three windbreak walls with the same height using numerical simulations. The results revealed that the windbreak wall geometric shape effects on the aerodynamic load coefficients varied according to the type of aerodynamic load and carriage marshalling positions but barely varied with yaw angles. The total drag coefficients of the train in the EW and RW were approximately 50–60% of that in the SW under the two smaller yaw angles and were only 30–40% for the largest yaw angle. For the absolute value of the side force and rolling moments coefficients, the maximum values for the head and middle cars both appeared in the RW, and the corresponding minimum values were obtained in the SW. The maximum and minimum values for the tail car were obtained at the SW and EW, respectively. The maximum of the rolling moment coefficient among three carriages in the SW was approximately 45–60% of that in the EW and only 30–40% of that in the RW. The time-averaged train surface pressure coefficient and flow patterns were similar between the EW and RW, which showed apparent differences from those in the SW. The SW provided a strong blocking effect on the incoming windward airflow and avoided the direct impact on the train. Compared with the RW, the uplifting effect of the EW's windward slope on the incoming flow further reduced the crosswind effect on trains. In addition, the dominating frequency characteristics of the aerodynamic loads were significantly affected by windbreak wall types. These findings provide a systematic understanding of the time-averaged aerodynamics of trains behind these three typical windbreak walls.

Effects of Pulsatile Flow Rate and Shunt Ratio in Bifurcated Distal Arteries on Hemodynamic Characteristics Involved in Two Patient-Specific Internal Carotid Artery Sidewall Aneurysms: A Numerical Study.

The pulsatile flow rate (PFR) in the cerebral artery system and shunt ratios in bifurcated arteries are two patient-specific parameters that may affect the hemodynamic characteristics in the pathobiology of cerebral aneurysms, which needs to be identified comprehensively. Accordingly, a systematic study was employed to study the effects of pulsatile flow rate (i.e., PFR−I, PFR−II, and PFR−III) and shunt ratio (i.e., 75:25 and 64:36) in bifurcated distal arteries, and transient cardiac pulsatile waveform on hemodynamic patterns in two internal carotid artery sidewall aneurysm models using computational fluid dynamics (CFD) modeling. Numerical results indicate that larger PFRs can cause higher wall shear stress () in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurysm generation than under smaller PFRs. The low and relatively high oscillatory shear index () could appear under a smaller PFR, increasing the potential risk of aneurysmal sac growth and rupture. However, the variances in PFRs and bifurcated shunt ratios have rare impacts on the time-average pressure () distributions on the aneurysmal sac, although a higher PFR can contribute more to the pressure increase in the ICASA−1 dome due to the relatively stronger impingement by the redirected bloodstream than in ICASA−2. CFD simulations also show that the variances of shunt ratios in bifurcated distal arteries have rare impacts on the hemodynamic characteristics in the sacs, mainly because the bifurcated location is not close enough to the sac in present models. Furthermore, it has been found that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period.

Experimental Study of Hydrodynamic Pressures Acting on a Submerged Gate

Vortical flow formed by a submerged hydraulic jump may produce significant hydrodynamic lift and drag pressures on a gate beneath the hydraulic jump. In this study, an experimental setup equipped with multi-pressure sensors was used to measure fluctuating impact pressures on the submerged gate for different flow conditions characterized by the inlet Froude number and submergence factor (S). Time-averaged and instantaneous pressure coefficients are evaluated based on simultaneous measurements of wall pressures at multiple locations, including those at the lip and downstream face of the gate. In particular, instantaneous lift pressure coefficients are observed to be independent of the submergence ratio for S > 0.6. It is found that low Froude number flows produce high surface pressure fluctuations and the dominant frequency of pressure fluctuations shifts to higher frequency as the Froude number increases. Pressure measurements for the free hydraulic jump suggest that the power spectra of lift pressure fluctuations are devoid of any significant energy level, whereas the resulting power spectra of the submerged flow exhibits significant energy level in the frequency range of 14-19 Hz. The proposed measurement system can be used for the in situ identification of hydrodynamic pressures acting on the gates in irrigation canals.

Optimization of sparse sensor placement for estimation of wind direction and surface pressure distribution using time-averaged pressure-sensitive paint data on automobile model

This study proposes a method for predicting the wind direction against the simple automobile model (Ahmed model) and the surface pressure distributions on it by using data-driven optimized sparse pressure sensors. Positions of sparse pressure sensor pairs on the Ahmed model were selected for estimation of the yaw angle and reconstruction of pressure distributions based on the time-averaged surface pressure distributions database of various yaw angles, whereas the symmetric sensors in the left and right sides of the model were assumed. The surface pressure distributions were obtained by pressure-sensitive paint measurements. Three algorithms for sparse sensor selection based on the greedy algorithm were applied, and the sensor positions were optimized. The sensor positions and estimation accuracy of yaw angle and pressure distributions of three algorithms were compared and evaluated. The results show that a few optimized sensors can accurately predict the yaw angle and the pressure distributions.