External Wind Speed Research Articles

Experimental and numerical investigation on spray cooling of radiator in fuel cell vehicle

In view of the heat transfer problem in fuel cell vehicle at climbing and high temperature environment, a method for spray cooling of the radiator using water produced by fuel cell is proposed. In order to evaluate the effectiveness of this method and predict the best working condition of spray at climbing and high temperature environment, a test bench was built to investigate the effects of four spray temperatures of 48 °C, 58 °C, 68 °C, and 74 °C on the cooling performance of the radiator. A three-dimensional model of the radiator was established, and the numerical simulation of radiator spray cooling was carried out based on the Euler–Lagrangian approach, and the validity and accuracy of the numerical simulation was verified by the experiments. Then the different spray angles and spray flow rates were considered to study the convective heat transfer coefficient of the radiator’s air side at climbing and high temperature environment, and the optimal working parameters were obtained. The results indicated that the spray at 74 °C still had a significant cooling performance on the radiator with the evaporation of the liquid film. The initial state of the spray hitting the surface of the radiator can be simulated, and the cooling performance can be evaluated by comparing the convective heat transfer coefficient of the air side of the radiator. The inclined spray is more effective than the vertical spray. At the interference of external wind speed of 40 km/h, the best heat transfer coefficient can be obtained with the 55° spray angle and the 9.44 g/s spray flow rate. This numerical simulation process can provide a reference for the design of fuel cell vehicle spray cooling system.

CFD investigation of a natural ventilation wind tower system with solid tube banks heat recovery for mild-cold climate

Passive strategies are increasingly being employed in buildings to minimize their total energy consumption and emissions. Wind tower, a natural ventilation device, can capture the wind flow from higher locations and supply the air into the buildings' indoor space without consuming electric power. However, its use in mild-cold climate is limited due to excessive heat loss and thermal discomfort, in particular, during winter. Limited research has been conducted to explore the pre-heating of the supply air in the wind tower to address the issue and potentially increase its adoption in mild-cold climates. Therefore, a novel wind tower ventilation system integrated with solid tube banks heat recovery (HR) is proposed in this research. By combining with a passive heat recovery device, a wind tower can be operated under winter conditions to improve indoor ventilation while reducing the building heating energy consumption. A three-dimensional computational fluid dynamics (CFD) model was developed to investigate the effects of the longitudinal pitch (SL) and the transverse pitch (ST) of the HR device on the ventilation and thermal performance. The overall performance of the wind tower was evaluated under different outdoor wind speeds. The results show that the heat recovery can be improved by reducing SL and ST, raising the supply fresh air temperature by up to 6.4 °C. Furthermore, the proposed wind tower can provide sufficient ventilation for a typical classroom occupied by 15 people when the external wind speed exceeds 3 m/s.

Transport process of outdoor particulate matter into naturally ventilated buildings

Natural ventilation of buildings can bring in fresh air, remove indoor air contaminants, and improve indoor thermal comfort. However, ventilation may also bring outdoor pollutants and/or aerosol into the buildings to affect the indoor air quality. This study uses a computational fluid dynamics model and a Lagrangian particle tracking model to investigate the transport process of outdoor particulate matter (PM) into a naturally ventilated building. The simulation results indicate that the entrance rate of outdoor PM contaminants is in the range of 7%–25%, depending on the particle size and the distance between the pollutant source and the building. The indoor concentration of PM2.5 decreases as the external wind speed and ventilation rate increase. In other words, sufficient natural ventilation can remove indoor particulate contaminants. In addition, the deposition rates in long buildings are larger than that in short buildings, owing to the sluggish airflow inside the long buildings. This study also estimates the time scales of particle deposition and ventilation-induced advection. The results reveal that the ventilation-induced airflow dominates the removal of fine particles PM1 and PM2.5, whereas the ventilation and deposition are equally important for coarse particle PM10.

Analysis on the Exhaust Air Recirculation of the Ventilation System in Multi-Story Building

In South Korea, the installation of a mechanical ventilation system is mandatory for the management of indoor air quality, and various studies concerning the ventilation rate and performance of the ventilation system have been conducted. However, only a few studies have been conducted regarding the recirculation rate of the ventilation system. If the appropriate arrangement of intake and exhaust vents in the ventilation system is not considered, the pollutants emitted from the circulation movement may be recirculated into the indoor environment and cause the degradation of the performance of the ventilation system. Therefore, this study aimed to quantitatively analyze the recirculation rate of pollutants emitted from a kindergarten building with an installed mechanical ventilation system in Seoul, South Korea, using computational fluid dynamics (CFD) analysis, and analyze the effectiveness of the guide panel installed for the prevention of the pollutants’ recirculation. The number of cases for the CFD analysis was set to a total of ten based on the ventilation rate in a mechanical ventilation system, external wind direction, and the existence of the guide panel for preventing the recirculation of exhaust air. The maximum recirculation rate of exhaust air without the installation of a guide panel was shown to be 20.0%. The maximum recirculation rate in the case where the external wind speed, direction of wind, and the ventilation rate were assumed to be identical to the other case but the guide panel for preventing the recirculation of exhaust air was assumed to be installed was 7.7%, 12.3% lower compared with the case with maximum recirculation rate.

Adaptive wind energy harvester with transformable bluff body

A novel adaptive wind energy harvester with a transformable bluff body responsive to external wind velocity is proposed in this study. This study is inspired by our finding that when an external wind velocity is lower than a specific (threshold) wind velocity, the energetic performance of an energy harvester with a certain cross-sectional shape of the bluff body is better than that with another shape and the reverse is true when the external wind speed is greater than the threshold. More specifically, the bluff body considered in the present study is composed of a prismatic cylinder and its cross-sectional shape is a triangle when the external wind velocity is below a certain threshold value. However, when the wind velocity exceeds the threshold value, the cross-sectional shape of the bluff body transforms into a W-shape in response to the wind velocity. In this study, an appropriate design process to develop the proposed system is established, and a physical prototype is fabricated. Thereafter, an associated mathematical model is developed and experimentally validated. The energetic and dynamic performances of the proposed system are thoroughly investigated and compared to systems with bluff bodies in three fixed cross-sectional shapes (square, triangle, and W-shape). As a result, the percentage increase ratio in the output power of the proposed energy harvester is found to be 23% higher than that of the system with a triangular bluff body, which is known to provide the best performance. This result indicates that the proposed system remarkably improves the energetic performance in comparison to the conventional system.

A full-scale field study for evaluation of simple analytical models of cross ventilation and single-sided ventilation

In this study, we evaluated several simple natural ventilation models of cross ventilation and single-sided ventilation with data measured in a full-scale field study in London. In the field study, the ventilation rate in a naturally ventilated office was measured using a tracer gas technique with CO2. Internal temperatures were measured using a vertical temperature array. The external temperature, wind speed and direction were measured at a nearby weather station. In addition, a 1:200 scale model of the urban area within 300 m of the test room was built in a wind tunnel to measure the pressure coefficients. The ventilation models were evaluated with input data from two sources. Wind data from a nearby airport and pressure coefficients from the literature were used, as is common practice. Alternatively, wind data measured at the local weather station and the pressure coefficients measured from wind tunnel experiments were used. The results showed that, regardless of the input data sources, the cross-ventilation model in general gives reasonable predictions. For single-sided ventilation, several empirical models were evaluated and poor predictions were obtained using the models. We discuss ways in which models of natural ventilation might be improved in the future.

External wind on the optimum designing parameters of a wall solar chimney in building

Solar chimney is a reliable renewable energy system that enhances the natural ventilation to reduce the energy consumption in buildings. Under the fact that previous optimization designs usually ignore the external wind, the impacts of external wind on the optimum designing parameters are then investigated. It is confirmed that external wind could affect its optimum designing parameters, which are different from those previously obtained value in the literature without considering the external wind. For the analysed wall solar chimney, it was known that previously obtained optimal cavity depth of 0.2–0.3 m is no longer applicable under the external wind, and the optimal value rises to 0.4–0.5 m, while the same applies to inlet height/area. Solar chimney performance is enhanced under the external wind, which is not only because of the incoming wind flow from the room opening but also the reduced air resistance. It was observed that increased solar intensity shows limited influences on the overall airflow characteristics. Solar chimney performance also presented a generally enhanced trend under a low external wind speed, but a strong wind could dominate its performance with limited fluctuation even though the wind angle is higher as 45°. It was known that the airflow rates through the solar chimney are largely hampered with a small cavity depth (i.e., smaller than 0.2 m) and inlet height under the external wind. And the airflow profiles are less affected when both of cavity depth and inlet height are bigger than 0.2 m. The obtained research outcomes could provide a technical guide on the optimization design of solar chimney in buildings.

Opening Size Effects on Airflow Pattern and Airflow Rate of a Naturally Ventilated Dairy Building—A CFD Study

Airflow inside naturally ventilated dairy (NVD) buildings is highly variable and difficult to understand due to the lack of precious measuring techniques with the existing methods. Computational fluid dynamics (CFD) was applied to investigate the effect of different seasonal opening combinations of an NVD building on airflow patterns and airflow rate inside the NVD building as an alternative to full scale and scale model experiments. ANSYS 2019R2 was used for creating model geometry, meshing, and simulation. Eight ventilation opening combinations and 10 different reference air velocities were used for the series of simulation. The data measured in a large boundary layer wind tunnel using a 1:100 scale model of the NVD building was used for CFD model validation. The results show that CFD using standard k-ε turbulence model was capable of simulating airflow in and outside of the NVD building. Airflow patterns were different for different opening scenarios at the same external wind speed, which may affect cow comfort and gaseous emissions. Guiding inlet air by controlling openings may ensure animal comfort and minimize emissions. Non-isothermal and transient simulations of NVD buildings should be carried out for better understanding of airflow patterns.

Modelling building infiltration using the airflow network model approach calibrated by air-tightness test results and leak detection

This paper presents a computational approach to air infiltration modelling and simulation validated by the blower door test results. In order to evaluate the potential of the airflow network method, three simulation models of the infiltration test were developed and calibrated by field measurements of leaked air change rate per hour at 50 Pa. Models were developed for existing building designs and constructed in low-energy standards differing in construction type and tightness. All leaks were precisely measured during field tests, defined as openings or cracks, numerically described and included in the model. The simulation results of calibrated models for other pressure differences revealed that the models’ accuracy is satisfactory. The differences between field tests and simulation results do not exceed 2.5%. Additionally, the calibrated models were used to estimate the infiltration heat losses of buildings in three different locations under continental climatic conditions. The results were compared with the steady-state method calculations made for the same building models and climatic conditions. It was proved that the steady-state method gives higher results of heat demand to cover infiltration losses than the simulation method. The final results depend on building location and vary between four and nine times. Practical application: The computational modelling and building performance simulations are increasingly commonly used in engineering design. The proposed method of air-tightness modelling and calibration can be used at any phase of a building’s lifecycle, from design and construction to exploitation and maintenance. Using the proposed techniques, it is possible to estimate more realistic processes of air infiltration and its effect on a building’s energy consumption in comparison with the steady-state method. Moreover, the analysis includes the dynamic effect of boundary conditions (external air temperature, wind speed and direction), as well as the effects of the building site and the surroundings.

Experimental Study on Smoke Exhaust of Circular Fire Lane in Underground Vehicle Base of Urban Railway

To discuss the natural ventilation design parameters of fire lane for underground car parking, a full scale experiment is adopted in this study to analyse the heat release rate and minimum clear height of underground fire lane. As a supplement, FDS numerical simulations are carried out to further study the smoke exhaust effect of natural ventilation under different external wind speed. Analytical results of full scale experiment and FDS numerical simulations show that the natural ventilation of underground circular fire lane of this case can effectively discharge the flue gas due to combustion. Through the results of this study, the natural ventilation design parameters of fire lane for underground car parking are determined primarily, which will provide reference for the fire protection design and approval of the underground car parking in the future.

Airflow patterns and turbulence characteristics above the canopy of a tomato crop in a roof-ventilated insect-proof screenhouse

Airflow patterns and turbulence characteristics inside a naturally ventilated screenhouse with tomato plants were experimentally investigated using 3D sonic anemometers simultaneously measuring air velocities at six horizontal positions in the space between the screened roof and the top of the canopy. The screenhouse had a flat roof and was ventilated through the roof only. Testing was carried out during about 3 weeks of crop development, under variable external conditions. The mean horizontal air velocity component above the canopy was generally lower than 0.20 Uoh (where Uoh is the mean horizontal external wind speed) and mostly in a direction opposite to the external wind. At low external windspeed, the airflow direction was not necessarily opposite to the wind direction. The vertical air velocity component was generally lower than 0.07 Uoh. The root mean square of the air velocity components, the turbulence intensity and the turbulence kinetic energy were much larger during the day than at night mainly due to the higher daytime effect of buoyancy and to a lesser extent due to the higher external wind speed. Spectral energy slopes of the velocity components were close to −5/3 during the day when wind speed was high. However, at night, when wind speed was low, the spectral energy slope of the velocity vector increased significantly. The integral length scales of turbulent eddies were greater in the horizontal than the vertical direction which is not surprising given the volume under consideration is bounded by the top of the canopy, the roof and the sidewalls.

Heat Loss Characteristics of Pipe Flange Joints: Experiments and Simulations

Abstract Sealing performance and heat loss are important factors for pipe flange joints (PFJs) subjected to medium or high temperatures. Heat loss is of great interest in practical engineering for uninsulated PFJs. Since an insulation layer may degrade the sealing performance of PFJs, heat loss of PFJs was tested and simulated considering various ambient temperatures of −10 °C, 0 °C, 10 °C, 20 °C, 30 °C, and 40 °C, with wind speeds of 0 m/s and 3 m/s and flange joint target temperatures of 200 °C, 300 °C, and 400 °C. It is worth noting that the experiments were performed during summer for high ambient temperatures and during winter for low ambient temperatures. As expected, the steady temperature slightly increases with the increase of external ambient temperature. For the same flange joint temperature, a 3 m/s wind speed decreases significantly the steady temperature, especially when the higher target temperature is applied. If the external wind speed is 3 m/s and the flange joint target temperatures are 200 °C, 300 °C, and 400 °C, respectively, the heat loss increases by approximately 38.4%, 30.7% and 23.6% when the ambient temperature changes from 30 °C to 10 °C. Moreover, the simulated temperatures agree well with the tested temperatures in most cases, and the average error is approximately 8%. The energy saving efficiency under the windless condition is approximately on average 26% higher than that with a wind speed of 3 m/s.

Modelling anti-icing of railway overhead catenary wires by resistive heating

Aggregation of ice on electrical cables and apparatus can cause severe equipment malfunction and is thus considered as a serious problem, especially in arctic climate zones. In particular, cable damage caused by ice accumulation on railway catenary wires is in wintertime a common origin for delayed trains in the northern parts of Europe. This study examines how resistive heating can be used for preventing formation of ice on metallic, non-insulated electrical cables. The heat equation and the Navier Stokes equations were solved simultaneously with FEM in 3D in order to predict the cable temperature as function of external temperature, applied voltage, wind speed, wind direction, and heating time. An analytical expression for the heat transfer coefficient was derived from the FEM simulations and it was concluded that the influence of wind direction can typically be neglected. Experimental validation measurements were performed on Kanthal cables in a climate chamber, giving temperature increase results in good agreement with the simulation predictions. The resistive heating efficiency, i.e. the ratio between applied electrical energy and resulting thermal energy, was found to be approximately 68% in this particular study.

Passive Heating and Cooling Potential Strategies: A Comparison between Moderate Summers and Warm Winters Climate Zones

In this work, a comparison between different potential natural ventilation strategies used in different climate zones are investigated. As an example of moderate summer climate zone, London city has been selected, while Dubai city has been selected as a warm winter climate zone. The influence of external wind speed and pressure was studied using Autodesk Flow Design Software. Then CFD simulations have been generated inside the building using IES Virtual Environment software to study the indoor ventilation (Micro-Flow analysis) and to demonstrate the success of the adopted potential strategies in enhancing the indoor climate conditions. Hourly Analysis Program (HAP) was used to calculate the cooling/heating load of the building and to check the energy savings. The results demonstrated that comfort conditions within the interior space of the building were met during certain months of the year using passive heating/cooling strategies alone (without the need of HVAC system). HAP energy modeling results showed that the annual space cooling for Dubai model dropped from almost 58,000 kW per year to almost 42,000 kW with a total energy savings of 18.6% (including all energy consumption parameters). On the other hand, London model results showed that the annual interior space heating dropped from almost 36,000 kW to almost 28,000 kW with a total energy savings of 16.4%.

Airflow assessment in a naturally ventilated greenhouse equipped with wind towers: numerical simulation and wind tunnel experiments

In this study, the air change rate and airflow distribution inside a greenhouse equipped with wind towers were analyzed using Computational Fluid Dynamics (CFD) simulations, considering different wind speeds (1–5 m/s) and incident angles (0–45°). The validation methods included smoke visualization, hot wire velocity point measurements, and Particle Image Velocimetry (PIV) measurements. The visualized and simulated flow regimes exhibited fair agreement. The average discrepancy between the hot wire velocity point measurements and simulated results was about 7.96%. The predicted vector fields in the inlet and outlet wind towers demonstrated good qualitative agreement with the corresponding PIV measurements. The discrepancy between the predicted and measured maximum air velocity in the inlet tower was 15%, while it was 3% in the outlet wind tower. At an external wind speed of 3 m/s and normal incidence angle, the average velocity of the airflow entering the greenhouse was 0.65 m/s (about one air change per minute), while the average air velocity in the greenhouse was 0.44 m/s. The average air velocity inside the greenhouse at a crop height (1 m) ranged from 0.3 to 1.8 m/s, which is within the optimum range of recommended air velocities for greenhouses.

Determination of a Methodology to Derive Correlations Between Window Opening Mass Flow Rate and Wind Conditions Based on CFD Results

This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations. The proposed methodology is useful for a wide spectrum of applications, in which no access to experimental data or conduction of several CFD runs is possible, deriving a simple expression of natural ventilation rate, which can be further used for energy analysis of complicated building geometries in 0-D models or in object-oriented software codes. The developed computational model simulates a building, which belongs to Rheinisch-Westfälische Technische Hochschule (RWTH, Aachen University, Aachen, Germany) and its surrounding environment. A tilted window represents the opening that allows the ventilation of the adjacent room with fresh air. The derived data from the CFD simulations for the air mass flow were fitted with a Gaussian function in order to achieve the development of an empirical equation. The numerical simulations have been conducted using the Ansys Fluent v15.0® software package. In this work, the k-w Shear Stress Transport (SST) model was implemented for the simulation of turbulence, while the Boussinesq approximation was used for the simulation of the buoyancy forces. The coefficient of determination R2 of the curve is in the range of 0.84–0.95, depending on the wind speed. This function can provide the mass flow rate through the open window of the investigated building and subsequently the ventilation rate of the adjacent room in air speed range from 2.5 m/s to 16 m/s without the necessity of further numerical simulations.

Assessing effects of wind speed and wind direction on discharge coefficient of sidewall opening in a dairy building model – A numerical study

The discharge coefficient (Cd) of an opening is an important parameter in the application of the orifice equation to calculate the airflow rate of naturally-ventilated buildings. It is questionable to regard Cd as a constant under varied external airflows for large openings that are often applied in dairy buildings. This study investigated the impact of external wind speed and wind direction on the discharge coefficient of the windward sidewall opening with various opening sizes for a scaled naturally-ventilated dairy building model. The investigations were performed with Computational Fluid Dynamics (CFD) simulations. A set of data from wind tunnel experiments with a building model was used for the CFD model validation. The simulation results indicated that the discharge coefficient was almost unaffected by outdoor wind speed but varied considerably with the wind direction. Lower Cd values were observed for smaller wind angles. The pressure distributions on sidewalls were non-uniform. It is concluded that in the application of the orifice equation in oblique wind directions and large openings, the discharge coefficient is required to be specified instead of using the constant value, and it is necessary to distribute enough pressure taps along the horizontal direction to obtain the representative pressure difference.

Association of flame-oscillation frequency under cross wind diffusion

Turbulent flame-oscillation frequency and combustion efficiency are the important parameters in combustion. It is a useful study to judge combustion efficiency by intuitive flame frequency. Based on a combustion wind tunnel experimental set-up, the variation law of combustion flame-oscillation frequency and combustion efficiency using external wind speeds was studied via the color flames image sequence of oil pan combustion and flue gas composition. The oscillation frequency was calculated with the upper edge of the fire plume which recorded flame image sequence using a high-speed video, combined the MATLAB image processing technique. The combustion efficiency was calculated combined with the C and H element mass of the liquid fuel in the oil pool and CO2 and H2O concentrations in the flue gas. The results show that the oscillation frequency of the flame revealed a tendency to increase followed by a decrease with increasing wind speed, while the overall trend of combustion efficiency increased first and then decreased. The combustion efficiency could be judged by observing the oscillation frequency of the flame image. In addition, the combustion efficiency may ensure in right way when the turbulence oscillation frequency of the oil pan flame ranged between 15 Hz and 18 Hz.

Airflow as a Possible Transmission Route of Middle East Respiratory Syndrome at an Initial Outbreak Hospital in Korea.

In this study, the results of an airflow investigation conducted on 7 June 2015 as part of a series of epidemiologic investigations at Pyeongtaek St. Mary’s Hospital, South Korea, were investigated. The study involved 38 individuals who were infected directly and indirectly with Middle East Respiratory Syndrome (MERS), by a super-spreader patient. Tracer gas experiments conducted on the eighth floor, where the initial patient was hospitalized, confirmed that the tracer gas spread to adjacent patient rooms and rooms across corridors. In particular, the experiment with an external wind direction and speed similar to those during the hospitalization of the initial patient revealed that the air change rate was 17–20 air changes per hour (ACH), with air introduced through the window in the room of the infected patient (room 8104). The tracer gas concentration of room 8110, which was the farthest room, was 7.56% of room 8104, indicating that a high concentration of gas has spread from room 8104 to rooms across the corridor. In contrast, the tracer gas was barely detected in a maternity ward to the south of room 8104, where there was no secondary infected patient. Moreover, MERS is known to spread mainly by droplets through close contact, but long-distance dispersion is probable in certain environments, such as that of a super-spreader patient hospitalized in a room without ventilation, hospitals with a central corridor type, and indoor airflow dispersion due to external wind.

Supervisory Control of Multirotor Vehicles in Challenging Conditions Using Inertial Measurements

We consider the problem in which a supervisor or remote pilot provides a real-time linear velocity reference to a multirotor aerial robot, either through a traditional remote control handset, a modern haptic interface, or semi-autonomous guidance control system. In all such cases, the goal is to servo-control the vehicle's velocity to the set point as quickly and as efficiently as possible. The challenge is to achieve this robustly in the presence of unknown wind disturbances and in situations in which the vehicle moves into global position system (GPS) denied environments (indoors, urban canyons, forests) where estimation of the vehicle's velocity is challenging. These situations include unclutterred environments, poor visibility environments caused by poor lighting, and poorly textured visual environments where laser- and vision-based sensors become unreliable. The approach taken is to develop a coupled nonlinear complementary velocity aided attitude filter that provides estimates of both the inertial and body-fixed frame linear velocities, as well as the attitude of a multirotor aerial vehicle, that functions effectively even when only the inertial measurement unit and barometric sensor measurements are available. When full inertial velocity measurements are available (from GPS, Vicon, or a vision system), the filter additionally estimates the external wind speed. In this paper, we formally present the proposed filter along with experimental results and a comparison of the filter to recent results in the literature and in situations in which inertial reference frame velocities are available intermittently. The proposed filter is computationally simple to implement, easy to calibrate and tune, and provides an excellent base level functionality for modern multirotor aerial robotic systems that will be required to function robustly in a variety of environments.