Crosswind Conditions Research Articles

Aerodynamic Load Analysis of Parts of Pantograph under Strong CrossWind

The pantograph-contact net model is established, and based on the N-S equation of the pressure correction procedure, the SIMPLE algorithm is used to solve the aerodynamic characteristics of different components of the pantograph under strong crosswind conditions. The effects of different crosswind speeds and different deflection angles on the aerodynamic load law of the pantograph components are discussed. Results show that among the various components of the pantograph, the aerodynamic drag and lift of the skateboard are the largest, and the lateral force of the lower arm and the bottom frame is also the largest. The pitching moment of the upper frame is the largest, and the overturning moment and the lateral moment of the sliding plate, the lower arm and the underframe are larger than before, which needs to be taken into consideration when we do calculations and optimizations. The research results can provide a basis for the operational safety and optimal design of high-speed pantograph under strong crosswind conditions.

Exergy and economic analysis of using the flue gas injection system of a combined cycle power plant into the Heller Tower to improve the power plant performance

Natural Draft Dry Cooling system (Heller Tower) is regarded as one of the frequently used cooling systems in steam power plants. The performance of these towers depends heavily on environmental conditions. Under wind conditions, due to the lack of symmetry in pressure distribution around the tower and the formation of wind cover phenomena on the top of the tower, the inlet flow rate to the tower drops and accordingly, the heat rejected by Heller Tower reduces almost by 40%, leading to a reduction in the power and efficiency of cooling tower and entire power plant. The injection of flue gas dissipated by the recovery boiler, which has the temperature of about 130°C, into a cooling tower at the combined cycle power plant is regarded as one of the recent methods proposed to improve the cooling tower efficiency under wind conditions. The present study aimed to examine various dimensions of the effect of flue gas injection into the cooling tower of a combined cycle power plant on the entire power plant, as well as its efficiency in terms of exergy and economic analysis. For this purpose, a Heller Tower was modeled by the CFD method. In addition, the amount of the cooling tower heat was calculated by the results of numerical analysis and used for the thermo-exergy simulation of various components of a combined cycle power plant in states of with and without flue gas injection under the tower design and crosswind conditions. The results indicated that the power generated by the steam cycle increased by a maximum of 7.92 MW due to the flue gas injection and under wind conditions. Finally, the results of the economic analysis represented the return on investment rate of 81.18 and 91.17% for two states of permanent and economic use, respectively, and the payback period of about one year.

Crosswind influence on cooling capacity in different zones for high level water collecting wet cooling towers based on field test

In order to evaluate the thermal performance of different zones for high level water collecting wet cooling towers (HWCTs) precisely, field test was conducted on one real HWCT equipped for a 1000 MW unit under different crosswind and water-spraying density conditions. In this paper, three parameters αs, αf and αr, which represent the cooling capacity of water-spraying zone, fillings zone and rain zone, respectively, are introduced to evaluate the crosswind influence on different zones. The variations of αs, αf and αr under windless and crosswind conditions were researched. The results demonstrate that, under windless condition, αf exceeds 88%. As crosswind velocity rises from 0.28 m/s to 4.79 m/s, when Q = 68646 t/h, αf decreases by 8.8%, while αs keeps around 10%, and αr increases by 5.6%. Additionally, it can be obtained that the cooling capacity of fillings is more outstanding under lower circulating water flow rate and small crosswind velocity conditions. Based on the test data, the fitting equations between αf and crosswind velocity are obtained. Briefly, the cooling capacity of different zones is obtained in this paper, and derived the changing rules of cooling capacity with different crosswind velocity, which can be used to guide the engineering design.

Aerodynamics and flight mechanics analysis of Airbus Helicopters\u2019 compound helicopter RACER in hover under crosswind conditions

In recent years, various helicopter manufacturers have been focusing increasingly on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics or aeroacoustic noise emission, to name only a few. In the following study, the behaviour of RACER in hover under the influence of crosswinds from eight different directions is investigated to support AH at the de-risking of RACER for this flight condition prior to the first flight. Therefore, a multidisciplinary, high-fidelity tool chain for coupled and trimmed aerodynamic simulations of the complete rotorcraft is applied. The presentation of the results is organized in three parts. In the first part, the flight mechanic behaviour is analysed and successful de-risking of ground clearance is shown. The second part focuses on the performance of the main rotor, the lateral rotors and the tail surfaces under wind conditions and shows that minimal power is required for headwind. In the last part, an analysis of the engines is performed, including a closer look at the inflow quality to the core engine and the convection of the hot exhaust gases.

Investigation of fire-driven cross-wind velocity enhancement

Understanding the aerodynamics associated with the interaction of fire and cross-wind flow is of great importance because the consequence may have major implications in building design against bushfire (or wildland fire) attacks. However, a fundamental understanding of how the interaction of fire and wind can alter free stream flow aerodynamic properties has remained elusive. The scope of this study is to examine the pool fire and wind interaction under fixed wind velocity condition. This study dissects the fundamental mechanisms of how the interaction of horizontal momentum flow with a vertical buoyant plume leads to enhancement of wind velocity in the horizontal direction at a certain elevation. Changes in flow aerodynamics caused by the interaction of fire and wind were analysed using the computational fluid dynamics approach. The mechanisms causing the changes were explained. A module was developed and added to the FireFOAM solver to evaluate flow acceleration due to the pressure gradient, gravity, and viscous effects. The chosen computational model was validated against two sets of experimental data, namely, a buoyant diffusion fire plume in still air and the other in cross-wind condition. The numerical simulation revealed that due to the interaction of fire and wind, there is a negative longitudinal pressure gradient across the plume axis, causing the flow to accelerate and the velocity profile to alter. It was also shown that the distortion in velocity profile depends on the location downstream of the fire plume. The height of the distortion increases whilst the magnitude of the distortion diminishes as the longitudinal distance from the fire source increases. Investigation of the effects of heat release rate on wind enhancement further showed that fire with a higher heat release rate causes a greater pressure gradient and a lower density, culminating in higher flow acceleration and consequently increase of wind enhancement.

Experimental study regarding the effects of forced ventilation on the thermal performance for super-large natural draft wet cooling towers

In this paper, an axial fan was introduced for thermal performance improvement of super-large natural daft wet cooling towers (S-NDWCTs), and the model experiment was performed to study the thermal performance of S-NDWCTs installed with an axial fan under windless and crosswind conditions. The experimental results manifested that, compared with traditional natural ventilation pattern, the thermal performance of forced ventilation is outstanding by analyzing the inlet air uniformity coefficient, cooling water temperature drop, Merkel number, etc. Moreover, the cooling water temperature drop is proportional to fan power under windless condition, and it enhances approximately by 12.06% at 3.77 W fan power, compared with natural ventilation pattern. Under crosswind conditions, the inlet air uniformity coefficient (ψ) and the water temperature difference on the water basin surface at forced ventilation pattern are more uniform than those of natural ventilation pattern, and ψ at 2.67 W condition increases by 8.08% compared with natural ventilation pattern while the crosswind velocity reaches to 0.6 m/s. Additionally, the cooling water temperature drop and Merkel number at forced ventilation pattern are also higher than those of natural ventilation pattern. Compared with natural ventilation pattern, these two parameters enhance by 6.46–13.35% and 0.69–5.62%, respectively within the experimental crosswind velocity ranges (0–0.6 m/s).

Aerodynamic loads and traffic safety of high-speed trains when passing through two windproof facilities under crosswind: A comparative study

Windbreak (WB) and anti-wind open-cut tunnel (AOT) are two common windproof facilities for high-speed railways in windy areas. This study aims to conducts a comparison of the aerodynamic loads and corresponding traffic safety of both windproof facilities when the high-speed train (HST) passes through them under crosswind conditions. The aerodynamic loads are obtained via CFD simulation, and safety indexes are generated through the wind-train-track dynamic analysis system. The main common characteristics between AOT and WB cases are as follows. Firstly, the fluctuation amplitudes of the five aerodynamic loads of each carriage in two periods (i.e., entry and exit) are remarkably greater than those in other periods (i.e., running completely in crosswind or windproof facilities). Secondly, the sudden increase in the fluctuation amplitudes of the safety indexes is an important factor in the reduced safety of HST traffic, and the derailment coefficient (DC) of the head carriage is the key to control the safety of the entire HST. Thirdly, the existence of the ends of windproof facilities narrows the original safety domain scope of the HST running only in crosswind. The main differences between AOT and WB cases are as follows. Firstly, the maximum fluctuation amplitudes of the five aerodynamic loads of each carriage in the WB case are generally greater than the corresponding values in the AOT case, whether entry or exit, under the same conditions of train and crosswind speeds. Secondly, the scope of safety domain when the HST passes through the ends of the WB is considerably smaller than that of the HST passing through the AOT ends, and the AOT is more effective than WB in terms of windproof effects. Thirdly, for the high-speed railway in the windy area with AOT and WB, the safety domain boundaries Vt = −6.3Vw + 343.3 and Vt = −10Vw + 350 can be used respectively to provide a reference for traffic safety command.

Optimal Safe Layout of Fuel Storage Tanks Exposed to Pool Fire: One Dimensional Deterministic Modelling Approach

Fire hazard is one of the main risks associated to fuel storage tanks in petroleum and in the petrochemical industries. Such a hazard includes pool fires in the storage tanks or in the bunds, fire propagation from the source tank to target tanks both in absence and in presence of wind, and also the cascading/domino effect due to confined and unconfined vapour cloud explosion and or BLEVE associated with the source tank. In the present work, a radiation shield of flowing water has been introduced at a distance from the source fuel storage tank to prevent the domino effect originating from this source tank, under fire, to the target fuel storage tanks in a tank farm. A simple one dimensional model has been developed from the steady state energy balance to simulate the safe distances (i.e. rim–rim distance) between fuel storage tanks containing class-I fuel (e.g. gasoline), both in presence and absence of a water-shield under no-wind and cross-wind conditions. The model predictions have shown that the maximum safe inter-tank separation distance of 28.42 m is anticipated at a wind velocity of 6 m/s, compared to 16.34 m in no-wind condition, beyond which the centroid of the parallelepiped (a solid-flame geometry) falls outside the base of the tilted flame geometry causing flattening of flame and a very sluggish increase in the flame tilt angle as the inverse of the Richardson number in the presence of wind velocity vector increases. Furthermore, the present one dimensional mathematical model has also been extended to show that introduction of a water-shield with an appropriate thickness (δopt) is able to prevent the propagation of radiation heat flux under both no-wind and cross-wind conditions to a much lower distance close to 8.34 m between tanks (measured from the centre of the source tank), than those predicted from the existing empirical models; viz. Point Source model and Shokrie-Beyler’s model.

Investigation of vehicle stability under crosswind conditions based on coupling methods

In this study, vehicle stability under crosswind conditions is investigated. A two-way coupling method is established based on computational fluid dynamics and vehicle multi-body dynamics. Large eddy simulation is employed in the computational fluid dynamics model to compute the transient aerodynamic load, and the accuracy of the large eddy simulation is validated with a wind tunnel experiment. The arbitrary Lagrange–Euler technique is used in the computational fluid dynamics simulation to realise vehicle motion, and a real-time data transmission method is employed to ensure effective exchange of data between the computational fluid dynamics and multi-body dynamics models. The robustness of the two-way coupling model is verified by changing the position of the vehicle centroid. The results of the two-way and one-way coupling simulations demonstrate that crosswinds significantly affect vehicle stability. There is a clear difference between the results obtained with the two methods, particularly after the disappearance of the crosswind. The main reason for the difference is that the interaction between the transient airflow and the vehicle movement is considered in the two-way coupling method. Therefore, investigations of vehicle stability under crosswind conditions should consider the coupling of transient aerodynamic force and vehicle movement.

Utilization of the lateral accelerated cross-wind to improve the cooling performance of a natural draft dry cooling tower

Cross-wind degrades the performance of a natural draft dry cooling tower (NDDCT). Based on the basic affecting mechanism, this paper introduces a wind collecting approach. By using a wind collecting duct, the lateral flow acceleration of cross-wind is broken up, and the lateral flow kinetic energy is utilized to increase the lateral and rearward static pressure outside the radiator inlet. By adoption of a CFD model, the effect of the wind collecting approach is investigated comprehensively. It is found that the wind collecting ducts could improve the pressure distribution around the radiator bundle, reinforce the lateral air intake, and reduce the intensity of mainstream vortices, so as to enhance the ventilation rate of a NDDCT. For an outstanding performance, the two-duct wind collecting scheme is suggested, which may assure a NDDCT working in an approximately wind free manner in all investigated cross-wind range, and increase the ventilation rate by ~63% under the high cross-wind condition, which may reduce the overall coal consumption by 23500~33500 tons annually for a 660 MW coal-fired unit. The numerical results are confirmed by a hot state modelling experiment conducted in a wind tunnel.

Thermal performance improvement of the three aligned natural draft dry cooling towers by wind breaking walls and flue gas injection under different crosswind conditions

The substantial objective of using circulating cooling water in a typical power plant is to remove the heat effectively from the vapor cycle and to expel it to the environment. One of the most popular cooling systems for this purpose is the natural draft dry cooling tower (NDDCT) which is widely used in regions with the shortage of water, such as Iran. Environmental conditions affect the Heller cooling tower's performance strictly. Temperature, density, and the mass flow rate of sucked air into the cooling towers will all influence their operation. To improve the cooling tower's performance and air suction capability, it is proposed to inject the steam generators' flue gas into the tower. In this study, a single natural draft dry cooling tower incorporating the flue gas duct is modeled to study the effect of flue gas injection on the sucked air flow rate and the radiator heat transfer. Considering the buoyancy effect term, for a 3-D incompressible flow, the Navier Stokes' equations, as well as the energy equation, are solved by computational fluid dynamic method (CFD) to obtain the airflow pattern inside and outside the tower as well as the heat transfer from the radiators. The tower is assumed to be equipped with windbreak walls in one case and without it in another case so that the effect of crosswind could be investigated. Having compared the thermal performance of the towers, the results show that the thermal deficiency is more pronounced for the towers in crosswind without any flue gas injection. It is also shown that the injection of the hot flue gas (with temperature of 130 °C) will increase air intake and the thermal performance of the towers which, in turn, results in the reduction of the outlet water temperature. The modeling is then extended to three aligned NDDCTs to determine the effect of flue gas injection in the presence of windbreak walls under crosswind condition. Consequently, a notable promotion had been observed in all three towers thermal performance but with different ratios.

Effects of crosswind and burner aspect ratio on flame characteristics and flame base drag length of diffusion flames

Experimental investigations were conducted to characterise the impacts of crosswind and burner aspect ratio on the flame evolution characteristics and flame base drag length of gas diffusion flames on rectangular burners. The burners have the same surface area of approximately 100 cm2. The tests to capture the flame base drag length were conducted three times for each condition with the differences between the original and repeated tests being less than 6%. The thermocouple readings were corrected for the effect of radiative and convective heat exchange with the surroundings. Overall, 84 independent test conditions were conducted on 4 different burner aspect ratios, 3 fuel supply rates and 7 crosswind conditions. The changing behaviour of the flame with different burner aspect ratios, heat release rates and crosswind speeds were carefully analysed. The appearance of “blue flames” in the upstream edge of the main diffusion flames just above the burner in relatively strong winds was analysed. Unlike the flame tilt angle and flame height which either increase (the former) or decrease (the later) monotonically with the increase of wind speed, the flame base drag length was found to increase with the wind speed firstly until a critical point and then decrease with further increase of the crosswind for a given heat release rate. This is thought to be due to the competing influence of thermal buoyancy and wind induced inertial forces. The transition point for the maximum flame base drag length with regard to crosswind was found to decrease with the increasing aspect ratio of the burner for a given heat release rate. A new physics-based correlation considering decay phase with the crosswinds was proposed for the flame base drag length incorporating all important physical factors including inertia force, fire induced thermal buoyancy, Froude number, dimensionless heat release rate and fuel/air density ratio. The proposed formulations were found to correlate well with the current measurements of gas burner fires as well as some published data in the literature for pool fires on the ground which were not used in their derivation.

Novel method for improving the cooling performance of natural draft wet cooling towers

A novel method for improving the cooling performance of natural draft wet cooling towers (NDWCTs) by installing air ducts in the rain zone was proposed for the first time. To study the effect of air ducts on NDWCTs and the associated mechanism, a 3D numerical model was established. The accuracy and credibility of the NDWCT model were validated. Based on the numerical model, the air temperature uniformity coefficient Cu,θ and the airflow rate G of the tower were computed to evaluate the effect of air ducts on tower aerodynamic field. The tower outlet water temperature t2 was assessed to clarify the effect of air ducts on tower cooling performance. This study found that air ducts improved both the aerodynamic field and the cooling performance of the NDWCT and that the improvement is quite dependent on the crosswind velocity. The optimal effect of air ducts achieved under windless conditions. To determine the effect mechanism of the air ducts, the distributions of air velocity, air-water ratio, air temperature, and water temperature on some representative sections of the tower were analyzed under both windless and crosswind conditions.

Numerical investigation for the influence of the car underbody on aerodynamic force and flow structure evolution in crosswind

To investigate the aerodynamic behavior of underbody structure in crosswind conditions, two numerical simulation models have been developed by using computational fluid dynamics method. First, to validate the accuracy of these models, the wind tunnel experiment of model with simplified flat underbody has been designed. The computationally predicted results of realizable k-e model show consistency with experimental data, and the correlation deviation of aerodynamic force is less than 10%. By using such model, the aerodynamic force and flow field of car under steady crosswind are simulated using underbody structure, and the influence on the aerodynamic characteristic has been analyzed. It can be found that the aerodynamic force increased significantly under different yaw angle. The physical mechanism response has been clearly shown by investigating the flow field around car body by vortices visualization technique. The results of this study can be served as a suggestion for studying the vehicle stability of high-speed under crosswind.

Semi-empirical ocean surface model for compact-polarimetry mode SAR of RADARSAT Constellation Mission

A semi-empirical model of the ocean surface is developed for the compact-polarimetry (CP) mode of Synthetic Aperture Radar (SAR) which will be a main product of the RADARSAT Constellation Mission (RCM), scheduled for launch in November 2018. The fundamental mechanism for the semi-empirical model is the interactions between sea surface waves and the radar microwave. Sea surface waves are generated by ocean surface winds and may be modulated by precipitation or oceanic processes, such as surface currents, internal waves (IWs), and surfactants (e.g. oil spill, and sea ice). Model results for normalized radar cross sections (NRCSs) induced by ocean winds are validated against a database we developed. The ocean wind vectors were observed by in situ buoys of the National Data Buoy Center (NDBC); the RCM NRCSs are obtained from a “CP simulator”, using composites of RADARSAT-2 quad-pol SAR images. We simulate the dependencies of the NRCSs on wind speeds and incidence angles, for up-wind (wind direction is 0°) and cross-wind (wind direction is 90°) conditions. And we report the potential abilities and limitations of ocean winds monitoring using the RCM CP mode, as well as suggest that the RV-pol should be suitable for hurricane monitoring in the future. As hurricanes containing high winds are generally associated with heavy rain conditions, we discuss the possible mechanisms for precipitation effects related to the RV- and RH- polarizations by simulating two effects on the ocean surface waves. Moreover, we suggest that the RCM CP mode is better able to monitor the ocean surface currents than the fully polarimetry SAR systems (e.g. RADARSAT-2), because of the associated large swath and the possible continuous images of three RCM satellites.

Analysis of crosswind aerodynamics for competitive hand-cycling

Competitive hand-cycling represents a unique case for cycling aerodynamics as the athletes are in a relatively aerodynamic position in comparison to traditional able-bodied cyclists. There are some aerodynamic similarities between both cycling disciplines, including wheel designs and helmets. The lack of research in hand-cycling aerodynamics presents the potential for significant improvements. This research analysed the aerodynamics of competitive hand-cycling under crosswind conditions using wind-tunnel experiments and Computational Fluid Dynamics (CFD) simulations. A range of yaw angles from 0° to 20° in 5° increments were investigated for two separate hand-cycling setups; a road race and a time-trial setup. A maximum drag increase of 14.1% was found from 0° to 15° yaw, for a hand-cyclist equipped for a road race. The three disk wheels used for the TT setup had a large impact on the lateral forces experienced by the TT hand-cyclist. At just 5° yaw and at 15 m/s, the drag and lateral forces for the TT setup matched closely, while this event did not occur until 15° yaw at the same velocity for the road setup. For 20° yaw, the ratio of the lateral force to drag force was 1.6 and 5.6 for the road and TT setups respectively.

Wind Effects and the Challenge to Enhance Thermal Performance of Three Aligned Natural Draft Dry Cooling Towers

The performance of natural draft dry cooling towers (NDDCTs) depends on the environmental conditions. Crosswind is known to have the most destructive effect, whereas the ambient temperature is marked as the next. A 3-D numerical model was developed to investigate the thermal performance of a single as well as three aligned units of NDDCTs under crosswind conditions. The computed results showed major discrepancies between computed velocity patterns and pressure fields around three aligned towers and those of the single tower due to windshield effect of neighboring cooling towers. The thermal performance losses for the single tower under crosswind showed higher values compared with those of towers in the aligned arrangement. The best thermal performance of three aligned NDDCTs was achieved when the crosswind was directed along the towers’ connection line.

Automatic landing system design via multivariable model reference adaptive control

The landing of a civil transport aircraft is one of the most critical phases due to parametric uncertainties and strong crosswind conditions. In this paper, separate controllers are designed for longitudinal and lateral-directional channels for the landing phase, which is divided into the final approach, flare, and decrab. A multivariable model reference adaptive control scheme is implemented with state feedback for output tracking. The safety and flight performance of the autolanding control system are demonstrated through Monte Carlo simulations of a nonlinear civil transport aircraft model.

Experimental study on the drag characteristic and thermal performance of non-uniform fillings for wet cooling towers under crosswind conditions

A thermal-state model experimental study was performed to investigate the drag characteristic and thermal performance of non-uniform fillings for wet cooling towers under crosswind conditions, several valuable performance parameters, including cooling efficiency, drag coefficient, ventilation rate, heat transfer coefficient and Merkel number, etc. were analyzed in this paper. Experimental researches proved that the non-uniform fillings are not sensitive to the crosswind, and can alleviate the adverse effect of crosswind on wet cooling towers. From the perspective of drag characteristic and thermal performance, the P4 pattern is the optimal non-uniform pattern under crosswind conditions, which has the higher ventilation rate, heat transfer coefficient, Merkel number and lower drag coefficient within the experimental crosswind velocity range. However, the P3 pattern has the lower evaporation loss and the outstanding relatively water-saving performance. Therefore, studies in this paper revealed that the optimal non-uniform pattern should be selected by terms of comprehensive consideration of energy conservation and water-saving. The P4 pattern is the optimal non-uniform pattern if giving the priority to energy conservation, and conversely, the P3 is the optimal pattern if considering water-saving characteristic preferentially.

Positive impact of a tower inlet cover on natural draft dry cooling towers under crosswind conditions

This study proposes a tower inlet cover to improve the performance of the small natural draft dry cooling tower (NDDCT) under crosswind conditions. CFD analyses are performed on a small NDDCT with tower inlet covers of different lengths, and the CFD model is validated against experimental results. The air temperature, air pressure, air flow and heat flux fields are presented, and the thermal performance for each heat exchanger and the NDDCT are obtained using CFD simulations. The CFD simulation results show that the high-pressure zone around the tower side wall, formed by the crosswind, causes the decrease in air flow through the tower and the deterioration in tower performance with a crosswind. The tower inlet cover can improve the tower performance in crosswinds by increasing the air flow of the heat exchangers. Tower inlet covers with lengths of 1.5 m, 3 m and 4.5 m improve the tower heat load by 40–65%, 70–130% and 85–230%, respectively, when the crosswind increases from 4 m/s to 12 m/s.