Upwind Research Articles

Application Of Onboard PIV To Front Wheelhouse Wake Behavior Under Stationary Crosswind Conditions

When driving a car, the driver and passengers may feel larger drag from a headwind, the steering wheel would be taken away by a crosswind or pushed by a tailwind. Anytime, anywhere, we will encounter various scenes with natural wind under real world conditions such as urban, suburb and highway. We will develop the appropriate vehicle by simulating these conditions to satisfy with various customer requirements. For vehicle aerodynamic research and development, we are simply running simulations in physical- and cyber-space, that is, wind tunnel facility and computational fluid dynamics to reproduce these real worlds. However, it is not easy to simulate these wind inlet conditions, such as the temporal change in crosswind, especially, in wind tunnel facility. The stationary yaw angle by rotating turntable would reproduce a crosswind, if there is no turbulent generator system like in Pininfarina and Swing in FKFS. Therefore, we focus on the unsteady and asymmetrical flow from the front wheelhouse of the vehicle with tire rotation. There is three-dimensional complicated flow that are interacted by the flow from various directions, such as the flow along the front bumper, the flow along the rotating tire and wheel, the blowing flow from the rotating wheel opening area and the flow from the tire house. These complicated flow produces the front wheelhouse wake along the body side that affects the vehicle aerodynamic performance. Furthermore, there are asymmetrical flows around the vehicle by different front wheelhouse wake in windward and leeward sides. The larger side wake increases the aerodynamic drag, and the fluctuating side wake may induce the instability of the vehicle handling stability. Here, the proposed onboard 2D-3C PIV measurement system in the previous study enables us to measure same measurement area along the vehicle body side without change in optical configuration effectively, that indicates to reduce the time by resetting the optical configuration. We will investigate what kind of flow field should be focused on and controlled to prevent the vehicle instability by investigating these asymmetrical flow field around the vehicle under crosswinds.

Indian ocean warming, extreme positive Indian Ocean Dipole events, and their impact on monthly Indian Monsoon rainfall from June to November in NMME models

Indian Ocean (IO) warming, the frequency of extreme positive Indian Ocean Dipole (EPIOD) events, and its impact on Indian monsoon rainfall (IMR) are more prominent in the recent era. A proper understanding of the relationship between the EPIOD and IMR is very important because two thirds of the people in India are dependent on agriculture and related economy. The primary focus of this study is on three main aspects: (i) analysing the monthly trend of sea surface temperature (SST) in the IO; (ii) the spatial variability of SST anomalies (SSTA) linked to the EPIOD and its impact on the IMR; and (iii) the factor responsible for the intensification of the EPIOD. These aspects are thoroughly assessed using 12 NMME models, comparing them with observations and reanalysis datasets from 1990 to 2020. The analysis reveals a warming trend in the central IO during June and July, with significant increases observed from August to November. Over the past 31 years, the central IO has experienced an approximate rise of 0.9 to 1 °C from June to November. Among the 12 models scrutinised, GFDL_FLOR_A, FLOR_B, and RSMAS_CCSM4 closely align with observed spatial trends. In contrast, models such as GFDL_SPEAR and NASA_GEOSS tend to overestimate these spatial trends. An increase in easterlies over the equatorial eastern IO was identified as a possible driver for the rising SST in the central IO during October and November. In response to EPIOD on the monthly spatial rainfall distribution over India, all NMME models often underestimate rainfall over the west coast and exhibit wet biases over the leeward side of the Western Ghats. Grid-wise skill scores for accumulated monthly rainfall demonstrated variations among NMME models, with GFDL_SPEAR, RSMAS_CCSM4, and other IC3 models showing higher skill. The interhemispheric pressure gradient (IHPG) has been identified as a precursor to EPIOD events. A positive IHPG from March to June is correlated with EPIOD occurrences from October to December. It is observed that half of the NMME models are capable of simulating a positive relationship between IOD and IHPG, consistent with the observed data.

Increasingly high-order hybrid multi-resolution WENO schemes in multi-dimensions

In this paper, a new type of increasingly high-order hybrid multi-resolution weighted essentially non-oscillatory (HMR-WENO) schemes is presented in the finite difference framework for solving hyperbolic conservation laws in one, two, and three dimensions. Based on the reconstruction polynomials defined on the one-point, three-point, five-point, seven-point, and nine-point spatial stencils, we reconstruct one zeroth degree reconstruction polynomial, one quadratic reconstruction polynomial, one quartic reconstruction polynomial, one sextic reconstruction polynomial, one octave reconstruction polynomial, and their derivative polynomials together with a new hierarchical bisection method to design a series of new troubled cell indicators which can precisely find all extreme points of associated unequal degree reconstruction polynomials located inside the smallest interval in one dimension. The new troubled cell indicators do not introduce any manual parameters related to different problems. The new hybrid methodology is divided into two parts: if all extreme points of the reconstruction polynomials are nonexistent or outside the smallest interval, the target cell is not a troubled cell and the simple linear upwind schemes are utilized to obtain high-order approximations. Otherwise, the target cell is a troubled cell and the MR-WENO spatial reconstruction procedures with excellent shock-capture ability are adopted. Then a series of HMR-WENO schemes are proposed by using these new troubled cell indicators, which can be easily expanded to arbitrarily high-order accuracies in multi-dimensions. The main benefits of these HMR-WENO schemes are their efficiency, since they could save about 22%-75% CPU time than that of the same order MR-WENO schemes when simulating some benchmark examples in multi-dimensions.

Upwind Scheme Using Preconditioned Artificial Dissipation for Unsteady Gas-liquid Two-phase Flow and Its Application to Shock Tube Flow

Upwind Scheme Using Preconditioned Artificial Dissipation for Unsteady Gas-liquid Two-phase Flow and Its Application to Shock Tube Flow

Mitigation of crosswind effects on high-speed trains using vortex generators

Vortex generators can enhance the operational safety of high-speed trains and offer effective anti-rolling performance. This paper investigates the influence of vortex generator installation angles on the aerodynamic characteristics of trains. The Improved Delayed Detached Eddy Simulation method is used to analyze the leeward side vortex structure. It is found that when the angle between the vortex generators and the relative wind is 30°, the rolling moment of the train is minimized, as it significantly reduces side forces while preventing excessive growth of lift force inducing rolling moment. The reduction in rolling moment of the train by vortex generators is attributed to the suppression of leeward side trailing vortices of the train, which delays flow separation at the roof of the train, inducing a downward trend in the separated flow. Dynamic Mode Decomposition reveals that vortex generators do not alter the stability of near-body trailing vortices but enhance the pulsatile characteristics of far-body trailing vortices, which do not affect the pressure distribution on the leeward side of the train.

Angle-of-attack characteristics of opposing jet for improving drag and heat reduction

While the opposing jet technique has the potential to achieve efficient drag and heat reduction, it can be severely affected by the incoming angle of attack. To analyze the angle-of-attack characteristics of opposing jet for improving drag and heat reduction, a three-dimensional blunt model was studied under various jet stagnation pressure ratios and angles of attack using the verified numerical method. The results showed that the enhanced reattachment shock on the windward side resulted in a higher pressure and temperature rise, which led to the deterioration of drag and heat reduction. Under the influence of the incoming angle of attack, the recirculation vortex transformed into a longitudinal vortex, resulting in a slanted U-shaped distribution of the surface pressure coefficient and Stanton number. Increasing the jet stagnation pressure ratio widened the coverage of the recirculation vortex on both the windward and leeward sides, which brought an improvement in drag and heat reduction. The interaction between the incoming angle of attack and the opposing jet caused a double-peak distribution of Stanton number due to the recirculation vortex reattachment and the compression of the incoming flow. The inclined opposing jet could reduce the peak values of pressure coefficient and Stanton number when subjected to the incoming flow with an angle of attack by spreading the recirculation vortex along the windward side. There should exist an optimal inclination angle that can effectively reduce the peak caused by the compression of the incoming flow without generating an excessive peak due to the recirculation vortex reattachment.

Experimental study on a combined sand barrier: Integration of porous mesh plate and novel porous sand-fixing bricks

Wind and sand disasters frequently impact the newly constructed railroad along the Hongyi line in Qinghai Province's Qaidam Basin. The existing wind and sand prevention measures, primarily comprising polyethylene (PE) nets, have shown limited effectiveness. To this end, this study introduces an innovative combined sand barrier: A new type of porous sand fixing bricks (PSBs) are made from local aeolian sand, arranged in a square grid like low vertical sand barrier, and combined with a high vertical porous mesh plate (PMP) to form a combined sand barrier. Wind tunnel experiments were conducted to optimize the combined sand barrier's structure. The results indicate that incorporating porous sand-fixing brick sand barrier (PSBSB) on the leeward side of the PMP substantially impacts the near-surface flow field and plays a crucial role in decreasing wind velocity while enhancing sand control. The PSBSB with five rows of PSBs, positioned 18H from the PMP's leeward side, maximizes windproof and sand control efficiencies. Notably, the PSBs exhibit excellent self-stability under wind load, eliminating the need for additional fixing measures. This combined sand barrier presents a replicable, cost-effective solution for wind-blown sand disaster prevention in aeolian sand regions like the Hongyi line, promising advancements in sand barrier technology.

Effects of windbreak types on aerodynamics of high-speed trains traversing from flat ground to semi-cutting and semi-embankment under crosswinds

Under the operation of strong crosswinds, the aerodynamic performance of high-speed trains (HSTs) will be seriously deteriorated when the transition section of flat ground and semi-cutting and semi-embankment (FGSCSE) is traversed, and the setting of windbreaks will help to slow down the impact of strong crosswinds on the trains. In this study, a three-dimensional coupled computational fluid dynamics numerical model to assess the aerodynamic performance of train–windbreak–FGSCSE–air system is developed. A comparative assessment is carried out to identify the variations in aerodynamic performance on the train carriage: no windbreak (NW), 50% ventilation windbreak (VW), and solid windbreak (SW), and the reasons for these variations are elucidated by examining the flow field structure's evolution. Furthermore, the operational safety of the train is discussed based on the indicator of wheel unloading ratio (fΔQ). Across the three distinct conditions, significant abrupt changes in aerodynamic load coefficients (ALCs) and the shedding of vortex structures are experienced by HSTs traversing the FGSCSE transition sections. Compared to the VW condition, the NW and SW conditions result in a greater number of shedding vortices on the leeward side and the tail of the train, and the VW condition results in the smallest magnitude of ALCs fluctuation. The power spectral density peak values of the aerodynamic loads follow the order: SW > NW > VW. Upon the train fully enters the subsequent operational environment, the VW condition has the smallest standard deviation of these coefficients. The standard deviations of CFy, CFz, CMx, CMy, and CMz for the head train in the VW condition are only 57.17% (46.81%), 55.85% (54.15%), 72.74% (34.62%), 57.99% (51.92%), and 44.60% (43.82%) of the corresponding values in the NW (SW) condition, respectively. In the NW, VW, and SW conditions, the fΔQ exceeds 0.9 when the wind speeds reach 30, 40, and 35 m/s, respectively. The windbreak with a ventilation rate of 30% performs the best, providing the most effective safety and stability for train operation.

Impact of Islands on Tidally Dominated River Plumes: A High‐Resolution Modeling Study

AbstractWhen flow passes over topographic features such as headlands and islands, island wakes can arise at the lee side of the flow. Island wakes are associated with enhanced biological productivity, increased mixing, and water mass transformation. While previous studies have mainly focused on the dynamical and biological effects of island wakes in the open ocean, here we focus on a large tidally‐dominated estuary with numerous islands, aiming to investigate the impact of such wakes on the offshore transport of river plumes. To this end, we use numerical simulations with unprecedented grid resolution in the plume region and around the islands. Our study area is the Pearl River Estuary, a region where satellite images indicate that oscillating wakes occur in the lee and far downstream of the islands. We show that submesoscale island wakes are ubiquitous in the plume‐influenced region and can affect a large area around the islands as the tidal flow reverses. These strong vorticity tails correspond well with the horizontal patterns of salinity gradients and salinity mixing. Sensitivity experiments show that these flow disturbances will largely decrease after the hypothetical “removal” of the islands. Analysis based on an isohaline coordinate framework shows that the isohaline surface area is limited by the presence of islands. It is proven that this “limiting” effect of islands on the plume extension is related to the salinity mixing and the associated diahaline water exchange.

Crosswind effects on thermal performance improvement of mechanical draft cooling towers with deflector plates

In practical operations, crosswinds significantly impact the thermal performance of mechanical draft cooling towers (MDCTs). This paper investigated the beneficial impact of deflector plates to mitigate the adverse crosswind effects on the thermal performance of MDCTs. The mechanism by which deflector plates reduce the crosswind effects was elucidated from both the windward and leeward sides. Additionally, the performance optimization with varying crosswind angles and speeds was comprehensively analyzed. Results revealed that at lower crosswind speeds, deflector plates effectively streamline airflow on both windward and leeward sides. However, when wind speeds exceed 4 m/s, the vortex region on the windward side expands, reducing the effectiveness of airflow optimization by deflector plates. Nonetheless, deflector plates consistently mitigate crosswind effects on the leeward side. Within the investigated parameters, at a 0° crosswind angle and 1 m/s crosswind speed, deflector plates significantly enhance thermal performance, manifesting in a 0.362°C reduction in outlet water temperature, a 10.77% increase in Merkel number, and a 2.48% improvement in cooling efficiency. This research establishes a theoretical framework for optimizing thermal performance in MDCTs with crosswind effects and provides valuable insights for engineering applications.

High-order second-generation wavelet upwind schemes with multiresolution self-adaptive capabilities for hyperbolic conservation laws

We introduce a novel system of high-order wavelet collocation upwind schemes utilizing a broad class of second-generation wavelets for hyperbolic conservation laws. These schemes possess multiresolution self-adaptive capabilities and are integrated into a meshfree framework. Unlike traditional high-order schemes that necessitate frequent variable transformations between physical and characteristic spaces involving numerous local projections, our schemes enable the direct discretization of relevant spatial derivatives in the physical space. The newly proposed schemes make the most use of wavelet properties, i.e., applying asymmetrical interpolating wavelets to achieve the upwind property and utilizing the symmetrical second-generation wavelets to preserve shapes of functions and obtain higher data compression rates. Numerical tests of which solutions contain strong discontinuities and different scale smooth structures are conducted to demonstrate the enhanced performance of the proposed schemes based on the second-generation wavelets. The proposed schemes can utilize only 9 % of the nodes in the WENO5 scheme to yield similar results when addressing the advection of a square wave and achieve the convergent solution for the two interacting blast waves problem without local characteristics projection. In comparison to conventional methods and wavelet upwind schemes based on the interpolating wavelets we previously introduced, the newly proposed schemes exhibit a significantly higher data compression rate and yield substantial computational savings without compromising accuracy.

A Péclet-robust Discontinuous Galerkin method for nonlinear diffusion with advection

We analyze a Discontinuous Galerkin method for a problem with linear advection–reaction and [Formula: see text]-type diffusion, with Sobolev indices [Formula: see text]. The discretization of the diffusion term is based on the full gradient including jump liftings and interior-penalty stabilization while, for the advective contribution, we consider a strengthened version of the classical upwind scheme. The developed error estimates track the dependence of the local contributions to the error on the local Péclet numbers. A set of numerical tests support the theoretical derivations.

A Study on the Thermodynamic Response of Double-Armed Thin-Walled Piers under an FRP Anti-Collision Floating Pontoon Fire

Abstract: As a potential fire scenario for bridge structures, the safety impact of an FRP anti-collision floating pontoon fire on bridge structures cannot be ignored. Taking the FRP anti-collision floating pontoon fire that occurred in a continuous rigid-frame bridge as the engineering background, the damage condition of the actual bridge fire scene was first investigated. In addition, FDS 5.3 software was used to simulate the FRP anti-collision floating pontoon fire scenario. Furthermore, the thermal–structural coupling method was used to investigate the thermodynamic response of double-armed thin-walled piers under fire. The results show that the FRP anti-collision floating pontoon fire causes localized concrete carbonization and spalling on the surface of the P2 pier, and the FRP anti-collision floating pontoons are largely destroyed. The fire has the greatest impact on the P2-1 pier, with the highest temperature of 667 °C on the windward side and the highest temperature of 326 °C on the leeward side. The temperature impact range is 6 m above the bearing platform, and the maximum damage depth of pier body concrete is 84.58 mm. The deformation and stress of the P2 pier under fire do not show significant changes and do not exceed the allowable limits for structural deformation and material stress. Therefore, the impact of this fire accident on the structural safety of the continuous rigid-frame bridge is minor. This study's results provide reliable guidance for the fire safety assessment and post-fire structural repair of the continuous rigid-frame bridge.

Effects of cooler shape and position on solidification of phase change material in a cavity

BackgroundFor balancing the imbalance between the energy supply and demand, phase-change materials (PCMs) provide an efficient means in terms of thermal energy storage and release. The performance of the energy storage is primarily dependent on the melting as well as the solidification process of the storage medium. Faster charging or discharging of the thermal energy is a primary concern for any thermal energy storage unit. On this background, the present study explores the novel approach for enhancing the solidification process of PCM considering the effects of cooler shape (namely semi-circular, triangular, and rectangular) and their position (namely top, side, and bottom) in a molten PCM-filled enclosure. The middle portion of the cooler wall is curved; whereas the remaining cooler wall is straight maintaining the same cooler wall length. MethodsTo analyze the solidification process, the involved transport equations are solved numerically following a finite volume-based computational approach using Ansys Fluent solver in conjunction with the appropriate boundary conditions. The computational model is generated for all the geometry comprising different shapes, as well as positions of the cooler wall. The third-order upwind scheme (QUICK) technique is utilized to discretize the momentum and energy equations. This scheme is well capable to accurately capture the gradients in the temperature and flow domains. Furthermore, the semi-implicit pressure-linked equation (SIMPLE) technique is utilised to address the pressure-velocity coupling. The resolved data are then saved as selective variables (U, V, and θ), which undergo post-processing to produce a local thermo-fluid flow field and extract average data. Significant findingsThe shape, as well as the position of a cooler, dictates the solidification process in an energy storage system. Thermal energy storage with a triangular-shaped cold wall positioned at the top could be opted as an appropriate design approach of an efficient energy storage system compared to a semi-circular or rectangular-shaped cooler model. The shortest solidification time of PCM occurs when the cooler wall is positioned at the top. The top position of the cooler having a triangular shape with higher Grashof number (Gr) values leads to a faster solidification process. Some ideas for possible future research areas in this field are provided after a comprehensive examination.

Numerical Study on Rotor–Building Coupled Flow Field and Its Influence on Rotor Aerodynamic Performance under an Atmospheric Boundary Layer

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural atmospheric conditions. A high-fidelity atmospheric boundary layer (ABL) model described by an exponential law is established herein. The solution of the coupled flow field is based on the Reynolds-averaged Navier–Stokes (RANS) equations, with the rotor’s rotation achieved through the overset grid method. Based on the dominant wind features, the building flow field is distributed into four regions, where the updraft along the headwind side impacts the rotor, bringing about a 76% increase in pitching moment. On the lateral side of the building, distorted rotor wake squeezed upward into the rotor disk, leading to severe blade–vortex interaction (BVI). During low-altitude hovering over rooftops, the mixing of building shed vortices with forward flow wakes causes the formation of a circulation region on the rotor’s windward side, resulting in a thrust loss of approximately 7.8%. Meanwhile, the flow environment on the leeward side of the buildings is more stable. Therefore, it is recommended that helicopters adopt a headwind approach during rooftop operations. However, an 11.4% loss in the average hover figure of merit is observed due to consistent thrust losses caused by the recirculation region.

Numerical approximation of parabolic singularly perturbed problems with large spatial delay and turning point

PurposeSingular perturbation turning point problems (SP-TPPs) involving parabolic convection–diffusion Partial Differential Equations (PDEs) with large spatial delay are studied in this paper. These type of equations are important in various fields of mathematics and sciences such as computational neuroscience and require specialized techniques for their numerical analysis.Design/methodology/approachWe design a numerical method comprising a hybrid finite difference scheme on a layer-adapted mesh for the spatial discretization and an implicit-Euler scheme on a uniform mesh in the temporal variable. A combination of the central difference scheme and the simple upwind scheme is used as the hybrid scheme.FindingsConsistency, stability and convergence are investigated for the proposed scheme. It is established that the present approach has parameter-uniform convergence of OΔτ+K−2(lnK)2, where Δτ and K denote the step size in the time direction and number of mesh-intervals in the space direction.Originality/valueParabolic SP-TPPs exhibiting twin boundary layers with large spatial delay have not been studied earlier in the literature. The presence of delay portrays an interior layer in the considered problem’s solution in addition to twin boundary layers. Numerical illustrations are provided to demonstrate the theoretical estimates.

An adaptive grid method for a two-parameter singularly perturbed problem with non-smooth data

In this paper, a two-parameter singularly perturbed problem with discontinuous source and convection coefficient is studied. This problem is discretized by using a first-order upwind finite difference scheme for which a posteriori error analysis in the maximum norm is derived. Then, based on this a posteriori error estimation, a grid iteration algorithm is designed to generate an adaptive nonuniform mesh. Finally, Numerical experiments are proposed to confirm that our proposed method is first-order uniformly convergent.

Numerical Analysis of the Effects of Different Window-Opening Strategies on the Indoor Pollutant Dispersion in Street-Facing Buildings

The idling of automobiles at street intersections can lead to pollutant accumulation which impacts the health of residents in street-facing buildings. Previous research focused on pollutant dispersion within street canyons and did not consider the coupling of indoor and outdoor pollutants. This paper employs the computational fluid dynamics (CFD) method to simulate the dispersion characteristics of vehicle emission pollutants in street canyons, primarily investigating the indoor and outdoor pollutant dispersion patterns under various window opening configurations (single-sided ventilation, corner ventilation, and different positions of the glass under corner ventilation). Additionally, the study considers the impacts of the aspect ratio and ambient wind speed. Studies have shown that corner ventilation is effective in reducing indoor pollutant levels. When the two window glass positions are far away from the center of the intersection, the average CO mass fraction in the single-sided ventilation room is reduced by 87.1%. The average indoor CO mass fraction on the leeward side decreases with the increasing wind speed and aspect ratio. At a wind speed of 8 m/s, the average indoor CO mass fraction on the leeward side decreases to 2.45 × 10−8. At an aspect ratio of 2, the indoor CO mass fraction on the leeward side decreases with increasing floors before stabilizing at approximately 4.77 × 10−9. This study suggests optimal window opening strategies to reduce indoor pollutant levels in street-facing buildings at street intersections, offering guidance to indoor residents on window ventilation practices.

Numerical simulation of the liquid film thickness distribution of horizontal tubes under cross-airflow

During the working process of the falling film evaporator, the airflow generated by evaporation process affects the falling film flow process. A three-dimensional model consisting of two horizontal tubes was conducted, which only considered the flow of one liquid column unit. The effect of cross-airflow on the liquid film thickness distribution of tube 1 and tube 2 in the jet mode was studied. The gas is air, the liquid is pure water, and the flow of gas and liquid begins simultaneously. The fluctuation and thickness distribution of the liquid film were analyzed. The research results indicate that liquid film fluctuation occur at the moment when the fluid falls from the first tube to the second tube, and continue to exist thereafter. When the airflow is applied, at l*=0.5, for the tube 1, the liquid film thickness from θ=45° to 90° areas is relatively flat; At l*=1, for the tube 2, the smallest liquid film thickness is located near θ=90° and 270°. The airflow has a certain inhibitory effect on the liquid film waviness on the windward side. The main reason why the liquid film thickness on the leeward side is greater than that on the windward side is due to the offset of the liquid column. The stability of the liquid column, which means that the liquid column does not offset, can ensure the stability of the falling film flow process.

Quantum simulation of Maxwell's equations via Schrödingerisation

We present quantum algorithms for electromagnetic fields governed by Maxwell's equations. The algorithms are based on the Schrödingerisation approach, which transforms any linear PDEs and ODEs with non-unitary dynamics into a system evolving under unitary dynamics, via a warped phase transformation that maps the equation into one higher dimension. In this paper, our quantum algorithms are based on either a direct approximation of Maxwell's equations combined with Yee's algorithm, or a matrix representation in terms of Riemann-Silberstein vectors combined with a spectral approach and an upwind scheme. We implement these algorithms with physical boundary conditions, including perfect conductor and impedance boundaries. We also solve Maxwell's equations for a linear inhomogeneous medium, specifically the interface problem. Several numerical experiments are performed to demonstrate the validity of this approach. In addition, instead of qubits, the quantum algorithms can also be formulated in the continuous variable quantum framework, which allows the quantum simulation of Maxwell's equations in analog quantum simulation.