Effects Of Ambient Wind Research Articles

Effect of ambient wind on horizontal flame spread over discrete multi-column fuel arrays

The flame spread behaviors of discrete charring fuels are significantly influenced by ambient wind. This paper studied the horizontal flame spread characteristics of discrete birch rod arrays under ambient wind experimentally and theoretically. Here, seven kinds of array spacings (denoted by S, 7–19 mm) and four kinds of wind speeds (denoted by U, 0.5–2.0 m/s) were designed to develop 28 experiments. The experimental results show that the flame inclination angle decreases as wind speed increases. The non-dimensional flame length and the non-dimensional heat release rate are also found to be correlated, and two ignition modes under the action of ambient wind were differentiated. The flame spread rate and wind speed have a linear relationship based on experimental data. The ratio of wind speed to fuel loading is introduced to further examine the variation of flame spread rate. In this article, a heat transfer model is established by simplifying discrete flame spread process and incorporating both radiative and convective heat transfer. A prediction model for flame spread rate is presented, which aligns well with the experimental results. Finally, the mass loss rate under the ambient wind is discussed.

Study on flame height and temperature distribution of double-deck bridge fire based on large-scale fire experiments

Vehicle fire is one of the important causes of bridge fires. This study conducted large-scale actual fire experiments by simulating heat release rates (HRR) of oil tank truck fires with 50 MW, 100 MW, and 200 MW in rectangular oil pans of varying sizes. The flame shape and spatial temperature distribution at different HRRs were studied bycontrollingvariables such as wind speed,firesource location, andlayer spacing. The results indicated that the actual HRR of the large-scale fire exceeded the anticipated value. In large-scale fire experiments, flame splitting into two main peaks was observed along the long side of the rectangular oil pan due to the coupling effect of ambient wind, long side, and sidewall effect of the diagonal web member. The average flame height was determined through image processing, and subsequently, a formula for predicting flame height during bridge fires under varying heat release rates was developed through the use of dimensionless analysis and feature length analysis. The spatial temperature distribution in the vertical direction of the axis of the center of the fire source, the temperature distribution of the diagonal web member and the bottom of the dense crossbeams, which are critical components of the bridge, were also analyzed. Furthermore, the conclusion that the flame in the lower bridge space which split into two main peaks is validated by the results. The results of this study can provide important theoretical support for investigating bridge fire resistance strategies.

Research on partition control of direct air‐cooling condenser based on multivariable Hammerstein CARMA model predictive control

AbstractPartition control of the fan array within a direct air‐cooling condenser (DACC) is recognized as a highly effective energy‐saving measure and a means to mitigate the adverse effects of ambient winds. This study focuses on the development of a dynamic partition model, which establishes the relationship between mass flow rate and fan array speed under windy conditions. The model is grounded in multivariable Hammerstein controlled autoregressive moving average (H‐CARMA) systems. Additionally, an innovative extended stochastic gradient algorithm, founded on the hierarchical identification principle, is introduced to estimate the model's unknown parameters. The recursive least square is employed as a benchmark to verify the accuracy and efficiency of the approach. Subsequently, leveraging the identified model, the model predictive controller based on the differential evolution method is designed to derive the optimal control law. Finally, simulation test and analysis are carried out to testify the effectiveness of our control strategy. The experiment result shows that the dynamic characteristics of the system have been significantly improved and the fan power consumption is reduced by 3.5% compared to the PID controller.

Temporal and spatial evolution of hydrogen leakage and diffusion from tube fittings on fuel cell vehicles under the effect of ambient wind

Hydrogen has become a competitive energy carrier owing to its high fuel value, cleanliness, and renewability. Fuel cell vehicles (FCVs) are crucial in achieving global carbon neutrality in the transportation sector. This study used Flame Acceleration Simulator (FLACS) software to model hydrogen leaks and diffusion from tube fittings of hydrogen systems with the numerical model validated by experimental data. The effect of wind direction on hydrogen leakage and diffusion in the chassis was investigated. Hydrogen leakage rates from the tube fittings under various pressures, tightening angles, and torques were determined; a release rate of 0.6 NL/min is considered a typical value for hydrogen leakage from the tube fittings of a 1.2-MPa hydrogen supply line. The results demonstrate that in windless conditions, the high concentration region with 1–2% vol. was located around the group of hydrogen storage tanks and that there was no flammable region in the entire chassis area. Wind accelerated hydrogen diffusion and reduced the extension range of the hydrogen envelope by 1–2% vol. Compared with longitudinal wind conditions, a crosswind can more effectively reduce the hydrogen concentration. Cutting off the hydrogen supply resulted in rapid contraction of the hydrogen envelope of 1–2% vol. within 5 s. These results have implications for installation of hydrogen sensors in the chassis of FCVs and the location of the blower for forced ventilation by first responders in the event of hydrogen leakage.

Operation optimization of cold‐end system of direct air‐cooled units considering the effect of environmental wind

AbstractAn air‐cooled island can significantly alter the heat transfer performance of an air‐cooled condenser due to the reflow of hot air caused by environmental wind. This can result in a considerable deviation between the backpressure calculated by traditional air‐cooled condenser models and the actual value. To address the issue, a research study was conducted on a 600‐MW direct air‐cooled unit. Numerical simulation methods were used to obtain the corresponding air flow rates and fan inlet air temperatures for each air‐cooled heat exchanger, which were then combined to establish a backpressure calculation model. From the above model, the backpressure prediction model and unit net output of full conditions were established using a backpropagation neural network. Therefore, taking the net output as the optimization objective, a genetic algorithm was used to compute the optimal backpressure and optimal fan speed in off‐design situations. Compared with traditional calculation approaches, the model produces backpressure predictions that were closer to the actual situation under the effect of ambient wind. The results indicate that both the optimal backpressure and fan speed were positively correlated with the exhaust flow and ambient temperature. It has been observed that when a unit was affected by different wind directions, the effect of the forwarding wind on the backpressure was smaller than that of other wind directions, especially under high‐load conditions. Moreover, the fan group operates close to full capacity under high‐temperature and high‐load conditions. Therefore, considering the influence of ambient wind, the obtained optimal backpressure and fan speed under variable working conditions were more realistic.

Effect of ambient wind on the performance of alpine downhill skier

Alpine skiing, especially alpine downhill, is one of the most extreme winter sports in terms of high-speed and narrow winning margin, and its tracks are always located in mountainous areas with high altitudes and complex ambient wind fields, resulting in a significant impact of ambient wind on the performance and the final ranking of alpine downhill skiers. In the present study, a method based upon the combination of field measurements, wind tunnel tests and kinematic simulations was used to evaluate the effect of ambient wind on the performance of an alpine downhill skier. Considering the effect of ambient wind, a kinematic model of the alpine skier-ski system was established, and the equations of motion for straight gliding and turning were deduced. Then, the Chinese National Alpine Ski Center (CNASC) downhill track was taken as a case study to investigate the effect of ambient wind on the gliding time using the proposed combined evaluation method. Field measurements and wind tunnel tests were performed to identify five critical ambient wind directions of 270°, 292.5°, 315°, 337.5° and 360°. Moreover, the wind speeds and the wind directions for 16 different measurement points of the downhill track were also obtained. The results of the modelling analysis showed that the finish time increased by 19.75% for the ambient wind direction of 270°, whereas the finish time decreased by 1.29% for the ambient wind direction of 360°.

Effect of ambient wind on the flame retardancy of intumescent coatings

Effect of ambient wind on the flame retardancy of intumescent coatings

Quantifying the COVID19 infection risk due to droplet/aerosol inhalation

The dose-response model has been widely used for quantifying the risk of infection of airborne diseases like COVID-19. The model has been used in the room-average analysis of infection risk and analysis using passive scalars as a proxy for aerosol transport. However, it has not been employed for risk estimation in numerical simulations of droplet dispersion. In this work, we develop a framework for the evaluation of the probability of infection in droplet dispersion simulations using the dose-response model. We introduce a version of the model that can incorporate the higher transmissibility of variant strains of SARS-CoV2 and the effect of vaccination in evaluating the probability of infection. Numerical simulations of droplet dispersion during speech are carried out to investigate the infection risk over space and time using the model. The advantage of droplet dispersion simulations for risk evaluation is demonstrated through the analysis of the effect of ambient wind, humidity on infection risk, and through a comparison with risk evaluation based on passive scalars as a proxy for aerosol transport.

Monte Carlo Simulation Methodology to Assess the Impact of Ambient Wind on Emissions from a Light-Commercial Vehicle Running on the Worldwide-Harmonized Light-Duty Vehicles Test Cycle (WLTC)

A Monte Carlo simulation methodology is suggested in order to assess the impact of ambient wind on a vehicle’s performance and emissions. A large number of random wind profiles is generated by implementing the Weibull and uniform statistical distributions for wind speed and direction, respectively. Wind speed data are drawn from eight cities across Europe. The vehicle considered is a diesel-powered, turbocharged, light-commercial vehicle and the baseline trip is the worldwide harmonized light-duty vehicles WLTC cycle. A detailed engine-mapping approach is used as the basis for the results, complemented with experimentally derived correction coefficients to account for engine transients. The properties of interest are (engine-out) NO and soot emissions, as well as fuel and energy consumption and CO2 emissions. Results from this study show that there is an aggregate increase in all properties, vis-à-vis the reference case (i.e., zero wind), if ambient wind is to be accounted for in road load calculation. Mean wind speeds for the different sites examined range from 14.6 km/h to 24.2 km/h. The average increase in the properties studied, across all sites, ranges from 0.22% up to 2.52% depending on the trip and the property (CO2, soot, NO, energy consumption) examined. Based on individual trip assessment, it was found that especially at high vehicle speeds where wind drag becomes the major road load force, CO2 emissions may increase by 28%, NO emissions by 22%, and soot emissions by 13% in the presence of strong headwinds. Moreover, it is demonstrated that the adverse effect of headwinds far exceeds the positive effect of tailwinds, thus explaining the overall increase in fuel/energy consumption as well as emissions, while also highlighting the shortcomings of the current certification procedure, which neglects ambient wind effects.

Visualization study on the effect of ambient wind on smoke layer height in chamber fires under natural smoke exhaust condition

Ambient wind often affects the smoke movement and natural smoke exhaust performance in enclosure fires. In this study, six wind speeds and twelve kinds of vent combinations are designed. 72 groups of experiments are conducted to investigate the coupling effects of vent combination and ambient wind speed during quasi-steady state of natural smoke extraction in chamber fires. Compared to the traditional Particle Image Velocimetry (PIV) method, a novel particle image flow field visualization (PIFFV) technique is proposed, and a smoke recognition algorithm for the determination of smoke layer height is developed based on two-dimensional OTSU method. Experimental results show that using the PIFFV method and the proposed algorithm, smoke layer height can be determined more accurately, in comparison to the N-percentage method. When the height of outlet is higher than that of inlet, the worst smoke control effect is found. When the air inlet is located on the windward side, the effect of natural smoke extraction is better under a reasonable wind speed than that in a windless condition. However, when the height of outlet is lower than that of the windward inlet, the optimal smoke control effect is achieved without ambient wind. In addition, when the inlet is arranged on the sideward side, ambient wind has a limited influence on smoke layer height with a lower outlet. Results of this study can provide references for the design of smoke control and ventilation system in room fires.

Consideration of cooling loss process of the emitter for radiative cooling

Sub-ambient daytime radiative cooling (SA-DRC) has been demonstrated by various advanced emitters in recent studies, which have attracted considerable attention from fundamental sciences and potential applications. Apart from emitter's unique radiative properties, the cooling loss of the emitter affects the performance of SA-DRC in actual applications. Although the emitter is fixed in an enclosure space to decrease the effect of ambient wind on the performance of cooling, the cooling loss of the emitter still exists, and an effective heat transfer coefficient between the emitter and ambient air has directly been widely used to predict the magnitude of the cooling loss power. However, this mathematical description is limited, which will lead to a controversial prediction in some cases. In this study, the cooling loss of the emitter was investigated based on a local environment. The simulation was conducted on the basis of four advanced emitters that were reported in recent studies, and the results show that the cooling loss of the emitter increases with the increasing interface temperature of the enclosure space that surrounds the emitter, which weakens the cooling effect of the emitter. A case study shows that the temperature reduction of an infrared-spectral-selective emitter could be degraded from −3.2 °C to 0.1 °C when the interface temperature increases from ambient temperature to 6 °C higher than ambient temperature, which implies that the cooling effect has been entirely destroyed.

Study on Mechanism of Series-Flow of Pollutants between Consecutive Tunnels by Numerical Simulation

The characteristics of series-flow between two consecutive tunnels with distance ranging from 20 m to 250 m are explored by computational fluid dynamics (CFD) parametric simulations of structure and operation parameters. The research indicates that series-flow can be considered the three-dimensional wall jet diffusion of upstream tunnel pollutants under the effects of the negative pressure area of the downstream tunnel entrance. The jet characteristics are primarily related to the tunnel distance between upstream and downstream tunnels and hydraulic diameters, and only influenced by the negative pressure in the area very close to downstream entrance where the tunnel air velocity ratio, i.e., the velocity of upstream tunnel air divided by the velocity of downstream tunnel air, decides the degree of the influence. If ignoring the effects of ambient wind and traffic flow, the series-flow ratio decreases with the increasing of parameters of the normalized tunnel distance, i.e., the tunnel distance divided by tunnel hydraulic diameter, and the tunnel air velocity ratio. Based on the three-dimensional wall jet theory, a series-flow model covering all jet characteristic sections is built. The experiment results indicate that the model applies to consecutive tunnels with any spacing and exhibits higher prediction accuracy.

Numerical study of hydrogen dispersion in a fuel cell vehicle under the effect of ambient wind

In the rescue of hydrogen-fueled vehicle accidents, once accidental leakage occurs and hydrogen enters the cabin, the relatively closed environment of the vehicle is prone to hydrogen accumulation. Excessive hydrogen concentration inside the vehicle cabin may cause suffocation death of injured passengers and rescue crews, or explosion risk. Based on hydrogen fuel cell vehicle (HFCV) with hydrogen storage pressure 70 MPa, four different scenarios (i. with opened sunroof, ii. opened door windows, iii. opened sunroof and door windows and iv. opened sunroof, door windows and rear windshield) under the condition of accidental leakage were simulated using computational fluid dynamics (CFD) tools. The hydrogen concentration inside the vehicle and the distribution of flammable area (>4% hydrogen mole fraction) were analyzed, considering the effect of ambient wind. The results show that in the case of convection between interior and exterior of the vehicle via the sunroof, door windows or rear windshield, the distribution of hydrogen inside the vehicle is strongly affected by the ambient wind speed. In the least risk case, ambient wind can reduce the hydrogen mole fraction in the front of the vehicle to less than 4%, however the rear of the vehicle is always within flammable risk.

Entransy analysis optimization of cooling water flow distribution in a dry cooling tower of power plant under summer crosswinds

The performance of natural draft dry cooling tower (NDDCT) of a coal-fired power generating unit is susceptible to ambient conditions, such as natural wind and temperature. An approach was proposed to relieve the adverse effects of ambient wind, which was the optimization of waterside flow re-distribution among heat exchangers of NDDCT under natural wind. With the help of entransy balance equations that described the heat transfer processes in each heat exchanger sector and condenser, all 20 influencing factors were considered to establish the optimization mathematical model of whole system, including both of the steam turbine subsystem and dry cooling system. A practical 660 MW dry cooling supercritical power generating unit was selected as object. The flow and heat transfer of NDDCT by natural wind effect were obtained numerically with verification. The results indicated that the performance of NDDCT could be improved by optimal distribution of waterside flow rate among the heat exchangers at any wind speed, especially at high wind speed. The comprehensive saving of power output coal consumption could be acquired although the pump power would raise by optimal water flow distribution. The decrease of coal consumption could reach 0.74 g/kWh at the natural wind speed of 12 m/s.

Square array of air-cooled condensers to improve thermo-flow performances under windy conditions

The thermo-flow performances of air-cooled condensers (ACCs) get deteriorated severely under windy conditions for the inherent defects of rectangular array of condenser cells. In this work, a square array of ACCs is proposed to restrain the unfavorable effects of ambient winds. By means of CFD methods and experimental validation, the air variable fields, mass flow rates and total heat rejections of the ACCs with two types of arrays at different wind speeds and directions are obtained and analyzed. The results show that the reverse flow in the upwind condenser cells and hot plume recirculation of the peripheral condenser cells are both weakened for the proposed square array under windy conditions. Accordingly, the mass flow rate and total heat rejection increase a lot especially in the wind direction of −90° with a heat rejection improvement of 25.21% at the wind speed of 16 m/s, showing that the thermo-flow performances of ACCs get improved thanks to the square array of ACCs. In the absence of ambient winds, the total heat rejection of ACCs in the square array is almost the same as the conventional array.

Effect of ambient wind on pressure wave generated by high-speed train entering a tunnel

Using three-dimensional, unsteady N-S equations and k-e turbulence model, the effect of ambient wind on the pressure wave generated by a high-speed train entering a tunnel was studied via numerical simulation. Pressure changes of the train surface and tunnel wall were obtained as well as the flow field around the train. Results show that when the train runs downwind, the pressure change is smaller than that generated when there is no wind. When the train runs upwind, the pressure change is larger. The pressure change is more sensitive in the upwind condition than in the downwind condition. Compared with no wind condition, when the wind velocity is 10 m/s and 30 m/s, the pressure amplitude on the train head is reduced by 2.8% and 10.5%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance is reduced by 2.4% and 13.5%, respectively. When the wind velocity is −10 m/s and −30 m/s, the pressure amplitude on the train head increases by 3.0% and 17.7%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance increases by 3.6% and 18.6%, respectively. The pressure waveform slightly changes under ambient wind due to the influence of ambient wind on the pressure wave propagation speed.

Effects of ambient wind on thermal smoke exhaust from a shaft in tunnels with natural ventilation

Abstract This study investigated the influence of ambient wind above the shaft opening on natural ventilation effectiveness in a tunnel by Large Eddy Simulation (LES), which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with systematically varying the ambient wind speed above the shaft opening and the longitudinal wind speed in the tunnel. The key heat and flow parameters inside and outside the tunnel and shaft, such as dispersion of smoke, temperature distribution, velocity vector field and mass flow rate of smoke exhausted by the shaft were investigated accordingly. The Reynolds number of the wind is in the range of 0.3–1 × 106 with velocity of 1–3 m/s and the Reynolds number of the smoke flowing in the tunnel and shaft is in the range of 0.1–1.7 × 106 with velocity of 1–5 m/s. The ambient wind above the shaft was found to have two opposite effects on the smoke exhaust from the shaft, namely a negative effect which restricts the smoke exhaust due to the perpendicular direction between the ambient wind and the originally vertical flowing smoke, and a positive effect which induces a negative pressure, in favour of accelerating the smoke exhaust. Moreover, both of these two effects will increase with increasing ambient wind speed above the shaft and they will compete each other simultaneously. The results will provide a theory support to guide the safe evacuation and smoke control in tunnels.

Performance improvement of natural draft dry cooling system by interior and exterior windbreaker configurations

Ambient winds are basically unfavorable to the thermo-flow performances of natural draft dry cooling system, and may result in a reduced thermal efficiency for the power generating unit in power plants, so it is of benefit to the natural draft dry cooling system to propose the measures against the adverse effects of ambient winds. For a typical natural draft dry cooling system, the computational models of the flow and heat transfer of cooling air coupled with the energy balances of circulating water and exhaust steam are developed, by which the performance improvement due to the interior and exterior windbreaker configurations is investigated. The flow and temperature fields of cooling air, the flow rate and heat rejection of each sector, the outlet water temperature of heat exchanger for the natural draft dry cooling systems with and without windbreaker configurations, and the corresponding turbine back pressures are obtained. The results show that the exterior windbreakers are superior to the interior ones in thermo-flow performances. The turbine back pressure can be reduced by the windbreaker configurations in the presence of ambient winds, especially at high wind speeds.

Triangularly arranged heat exchanger bundles to restrain wind effects on natural draft dry cooling system

It has been commonly recognized that the crosswind may deteriorate the cooling performance of the natural draft dry cooling system with vertically arranged heat exchanger bundles around the circumference of dry-cooling tower. With the purpose for restraining the adverse effects of ambient winds, a novel triangular configuration of heat exchanger bundles is proposed in this work. The air-side flow and heat transfer models coupled with the circulating water heat transfer process are developed for two kinds of natural draft dry cooling systems with the conventional circularly arranged and novel triangularly arranged heat exchanger bundles, by which the flow and temperature fields, mass flow rate of cooling air, outlet water temperature of heat exchanger and turbine back pressure are obtained. Three wind directions of 0°, 90°, and 180° are investigated at various wind speeds for the natural draft dry cooling system with triangularly arranged heat exchanger bundles, which are compared with the conventional system with circularly arranged heat exchanger bundles. The results show that the thermo-flow performances of the natural draft dry cooling system with triangularly arranged heat exchanger get improved significantly at high wind speeds and in the wind direction of 180°, thus a low turbine back pressure can be achieved, which is of benefit to the energy efficiency of the power generating unit. The natural draft dry cooling system with triangularly arranged heat exchanger is recommended to apply to the regions with strong prevailing winds all year around.

A novel layout of air-cooled condensers to improve thermo-flow performances

Ambient winds are generally unfavorable to the thermo-flow performances of air-cooled condensers in power plants. More emphases are placed to weaken the negative effects of ambient winds, but no layout alternative of air-cooled condensers is considered. In this work, a novel vertical arrangement of air-cooled condensers is proposed on the basis of a 2×600MW direct dry cooling power plant, which can weaken the adverse wind effects and utilize the wind power to improve the cooling capacity of air-cooled condensers. By means of the CFD simulation and experimental validation, the flow and temperature fields of cooling air for the vertically arranged air-cooled condensers at ambient winds are obtained. The mass flow rate, inlet air temperature and turbine back pressure are computed and compared with the traditional air-cooled condensers. The results show that the flow rate of the novel air-cooled condensers increases conspicuously compared with the current ones both in the absence and presence of winds. In the wind directions of 60° and 90°, the off-axis flow distortions of axial flow fans are greatly weakened and the average inlet air temperature of the novel air-cooled condensers is reduced and almost equals the ambient temperature. The thermo-flow performances of the air-cooled condensers are improved, thus the turbine back pressure is reduced by the novel layout of air-cooled condensers.