Three-dimensional Ultrasonic Anemometer Research Articles

Correction method for a shipborne ultrasonic anemometer in measuring the refractive index structure constant in a marine environment

The atmospheric refractive index structure constant (C n 2) was measured in a coastal region using a shipborne three-dimensional ultrasonic anemometer and a micro-thermometer. The results showed that the C n 2 measurements from both instruments were generally consistent but deviated in some cases, especially as the wind speed increased. Careful examination of the data revealed that this was due to noise introduced by wind-induced high-frequency oscillations of the extended arm carrying the ultrasonic probes, which also resulted in higher energy levels in the high-frequency region of the temperature spectrum. To address these issues, an attempt was made to filter the temperature data using a first-order low-pass filtering (LPF) algorithm. For our case, the corrected temperature spectrum reflects a reasonable distribution of turbulent energy at different frequencies, making it obey the −5/3 power law of Kolmogorov turbulence within the inertial subrange. In addition, the C n 2 values estimated from the corrected temperature data showed excellent agreement with the micro-thermometer measurements. The findings of this study provide experience and guidance for the measurement of optical turbulence in the marine environment.

A Study on the Depositional Law of Road Cutting in the Tengger Desert

In this study, the characteristics of wind-blown sand in the hinterland of the Tengger Desert and the regularity of sand deposition in road cutting are studied by combining a field test and numerical simulation. Firstly, the meteorological observation system is used to obtain the long-term monitoring of the Tengger Desert hinterland, and the perennial wind speed, wind direction, and strong wind period are obtained. Then, a three-dimensional ultrasonic anemometer and stepwise sand accumulation instrument are used to measure the transient wind-blown sand velocity and density at the top of the cutting slope, which provide the basis and verification for the numerical simulation. Finally, Fluent software (2020R2) is used to establish two numerical models with and without grading. Based on Euler’s two-fluid theory and fluctuating-wind user-defined functions, the movement of wind-blown sand in the cutting section of the desert hinterland is simulated, and the regularity of sand accumulation in the cutting section is obtained. The main conclusions are as follows: (1) The strong wind period in the hinterland of the Tengger Desert in 2021 mainly occurs from April to August, and the mainstream wind direction is concentrated in the WSW and SW directions. (2) The sand in the hinterland of the Tengger Desert is mainly medium–fine, and the particle size range is mainly concentrated at 0.075–0.250 mm, accounting for 98.2% of the total sand; the curve of the wind-blown sand density with height is oblique and L-shaped. (3) The method of grading excavation is beneficial to reduce the sand accumulation rate on the road’s surface.

Copper oxide particle emission and the spread in a public washroom from a high-speed jet air dryer

The high-speed jet discharged by hand dryers with brushed motors may release hazardous particles. In this study, the particles released from the hand dryer were trapped using high-efficiency particulate air filters for chemical composition analysis in a small test room. A manikin was placed to mimic a user standing in front of the dryer. Number and mass concentrations of the released particles were measured to estimate the particle emission rates and inhalation exposure. The particle emission rate reached 2.64 × 106 particles/s when starting the dryer. The released particles were found to contain a copper element, subsequently extrapolated to copper oxide. Secondly, in the large test room, jet airflows were measured using a three-dimensional ultrasonic anemometer. The results revealed that the horizontally placed palms caused the discharged jets to bend toward the human body, resulting in an upward motion of the air into the breathing zone. After running the dryer for 30 s, the peak mass concentration in the breathing zone for particles with a less than 2.5-μm diameter was 13.1 µg/m3. Installing high-efficiency particulate air filters to the air outlets of hand dryers was found to be effective in minimizing the exposure to CuO.

A comparison of the aerodynamic characteristics of four kinds of land surface in wind erosion areas of northern China

Aerodynamic characteristics is a crucial factor influencing soil wind erosion, which is closely related to the properties of surface roughness elements. In the expansive arid and semi-arid northern China, grassland, farmland, mobile sandy land, and gobi are the main land surface types that suffer wind erosion to varying degrees. To investigate the aerodynamic characteristics of different surfaces, we used three-dimensional ultrasonic anemometers to observe the near-surface wind speed above grassland, farmland, mobile sand, and two types of gobi surfaces in areas of northern China (a total of five observation sites). We compared the aerodynamic characteristics of the five surfaces and their causes (i.e., the surface roughness length, wind speed pulsation, turbulence intensity, and drag coefficient), and analyzed how surface roughness elements weakened the airflow. The roughness length was greatest for grassland, followed by farmland, sand, fine gobi, and black gobi. The pulsation intensity of near-surface wind speed increased linearly with increasing wind speed at all sites. At a given wind speed, increasing roughness length increased the pulsation intensity of wind speed. The probability distributions for the drag coefficient and turbulence intensity of the five surfaces followed a positively skewed distribution. The drag coefficient and turbulence intensity were greatest for grassland, followed by farmland, sand, fine gobi, and black gobi surfaces. The drag force exerted on the roughness elements increased with increasing wind speed, but the ratio of drag force exerted on the roughness elements to the total drag force (τR/τ) for flexible roughness elements (i.e., plants) increased as the wind speed increased; for rigid roughness elements, τR/τ decreased with increasing wind speed. This confirms that the shelter capability of flexible roughness elements against soil wind erosion increases with the increase of wind speed, while that of rigid roughness elements is opposite.

Analysis and assessment of factors affecting air inflow from areas adjacent to operating rooms due to door opening and closing

Operating rooms usually work with positive differential pressure in order to prevent the entry of contaminated air from adjacent areas and so maintain asepsis. Nevertheless, the opening of doors causes this pressure difference to disappear and means that contaminating agents can enter from adjacent areas. As a result, a knowledge of air flow pattern behaviour during the door opening and closing cycle is key to understanding the risk of infection and contamination in the operating room. The objective of this study is to quantify the air flow that enters the operating room during a complete door opening and closing cycle. We specifically study two operating rooms equipped with a heating ventilating air conditioning system: one with turbulent air flow and the other with laminar air flow. We assess the influence of the type of door - hinged and sliding – for different origin values of flow exhaust fan regulation. In order to perform the measurements, a three-dimensional ultrasonic anemometer that measures the magnitude and direction of the instant air velocity on the doorway of the door was used. Analysis of the results shows that the door opening and closing process leads to air entering the operating room from the adjacent areas in all of the cases studied, regardless of the ventilation system used. Sliding doors are seen to reduce the amount of air entering from the adjacent area in all the scenarios tested. Sliding doors are thus considered the preferred option in operating rooms.

Experimental study on gas diffusion in subway station

In this paper, three-dimensional ultrasonic anemometer and multi-channel anemometer have been used to monitor the flow field of a subway station in Beijing. Based on releasing sulfur hexafluoride (SF6) in the station hall, the gas transmission and diffusion range have been studied. The results show that under the natural ventilation, the gas diffusion would be controlled by a regular mainstream field. Because of obvious subsidence heavy gas tends to accumulate on the ground. The airflow on the north side of the platform is stable, which may be the main channel for gas diffusion and the gas will not be transmitted downward to the platform. As a result, during emergency response During emergency disposal, it is necessary to set an evacuation path opposite to gas diffusion. Besides, it is forbidden to turn on the top smoke exhaust system to avoid the transmission of pollutant on the ground to the breathing height.

Flow Distortion Effects of a Three-Dimensional Ultrasonic Anemometer and Its Impact on Measurements

The sonic anemometer is widely recognized as a precise and accurate instrument for measuring and studying atmospheric wind speed and turbulence that works on the principle of measuring the difference in the transit time of acoustic pulses along a known path length. Desirable characteristics of the sonic anemometer include lack of moving parts, linear dynamic response, and good directional response. However, the sensor probes and support structures inevitably lead to a deformation of the flow field being examined resulting in transducer shadowing and flow distortion errors. An empirical method of determining the effects of flow distortion errors on measurements is utilized. While deviations in the horizontal wind are negligible, investigations clearly indicate the need for correction of raw data on vertical wind measurements. Simulations have been conducted using a synthetic time series to determine the impact of observed errors on turbulence, with indications that measurements have a dependence on the angle of attack. Using the series at angles of elevation varying between -12° and 12°, a deviation in turbulence by over 30% is observed for certain wind directions. Matrices derived from the errors at different angles of attack have been used to correct standard ten-minute time series of field data resulting in a decrease in the measured turbulence strength by between 7 and 10%.

Comparison of forward and backward Lagrangian transport modelling to determine methane emissions from anaerobic digestion facilities

In biogas plants, where biological treatment of organic matter by anaerobic digestion (AD) is performed, as well as in plants for upgrading of biogas to biomethane, there might be emissions to air from different parts of the plants. Precise and comparable methods to quantify methane (CH 4 ) emissions from biogas plants are necessary to evaluate mitigation strategies and to generate more accurate emissions factors for national emission inventories in the context of the United Nations Framework Convention on Climate Change (UNFCCC) reporting. The main objective of this study was to provide recommendations for the measurement and modelling procedures of inverse dispersion modelling (IDM) to assure comparability of CH 4 emissions among diverse approaches and AD facilities. Two Lagrangian stochastic dispersion models were used operating in forward (LASAT) and backward (WindTrax) mode based on open-path concentration and meteorological data acquired by three international measurement teams at two biogas plants. The sensitivity analysis of the modelling systems regarding input parameters and setups (e.g. source configuration, terrain, sampling distance from the site, different combinations of wind data) showed that in WindTrax (backward mode) the measurement speed of meteorological parameters (via three-dimensional ultrasonic anemometer) had the largest influence on the calculated emission estimates, while in LASAT (forward mode) the assumption of the source configuration greatly affected the flux estimates. The used concentration data (e.g. location of observations, measurement mode of background concentration) was critically important to the success of IDM. The CH 4 emission rates from the AD facility in flat terrain (plant 1) calculated with both Lagrangian models by IDM showed good agreement with the DIAL (Differential Absorption Light Detection And Ranging) method and methane release tests (deviation in the range of 10–20%) when using best fit configurations (e.g. volume source in LASAT, area source in WindTrax, optimal measurement fetch). In moderately complex terrain (plant 2), the retrieval rates of controlled CH 4 releases, and thus the certainty of flux estimates of both dispersion models tended to decrease without the use of a terrain model. • First comparison of emission results inferred with LASAT and WindTrax. • Concentration and meteorological data obtained by three independent measurement teams. • Evaluation of sensitivity of the modelling system to input parameters and setups. • Recommendations for measurement and modelling procedure. • Uncertainty of ±10–20% for both models in flat terrains using best fit configurations.

Effects of forced air warming systems on the airflow and sanitation quality of operating rooms with non-laminar airflow systems

Background: Previous studies have demonstrated that forced air warming (FAW) can be used safely in operating rooms with laminar airflow (LAF) ventilation systems. However, the effects of FAW on the airflow at surgical sites under non-LAF (nLAF) ventilation systems remain unclear, as nLAF systems generate outlet-to-inlet multidirectional airflows of the air conditioning system. Here, we evaluate the effects of FAW on the airflow and sanitation quality in surgical fields with nLAF ventilation systems. Methods: The airflow speed and direction were measured using a three-dimensional ultrasonic anemometer. Sanitation quality was evaluated by measuring the amount of dust particles after the activation of air conditioning. Results: FAW caused no meaningful airflow (> 10 cm/sec) and did not diminish the sanitation quality in the surgical field separated by the anesthesia screen. Above the head area, the upward FAW airflow was not counteracted by nLAF, which caused an upward airflow at the edges of the operating table, originating from outside of the operating table and the floor. Conclusions: Sanitation quality was kept under FAW working even in an nLAF-equipped OR. According to the inlet/outlet layouts of nLAF, the upward FAW-induced airflow in the head area was not counteracted, and the upward airflow from the floor induced by the air conditioner outlet could be detected.

Estimation of Sensible Heat Flux and Atmospheric Boundary Layer Height Using an Unmanned Aerial Vehicle

In this work, sensible heat flux estimated using a bulk transfer method was validated with a three-dimensional ultrasonic anemometer or surface layer scintillometer at various sites. Results indicate that it remains challenging to obtain temperature and wind speed at an appropriate reference height. To overcome this, alternative observations using an unmanned aerial vehicle (UAV) were considered. UAV-based wind speed and sensible heat flux were indirectly estimated and atmospheric boundary layer (ABL) height was then derived using the sensible heat flux data. UAV-observed air temperature was measured by attaching a temperature sensor 40 cm above the rotary-wing of the UAV, and UAV-based wind speed was estimated using attitude data (pitch, roll, and yaw angles) recorded using the UAV’s inertial measurement unit. UAV-based wind speed was close to the automatic weather system-observed wind speed, within an error range of approximately 10%. UAV-based sensible heat flux estimated from the bulk transfer method corresponded with sensible heat flux determined using the eddy correlation method, within an error of approximately 20%. A linear relationship was observed between the normalized UAV-based sensible heat flux and radiosonde-based normalized ABL height.

Effects of the Surface and Atmospheric Stability on the Integral Length Scale at a Coastal Site

We analyze the effects of surface heterogeneity and atmosperic stability on the velocity integral scale at La Paloma, a coastal location in Uruguay, using measurements from three three-dimensional 32-Hz ultrasonic anemometers at heights of 11 m, 40 m, and 66 m for the period December 2016–April 2017. The vertical profiles of heat and momentum fluxes indicate that flow from the sea develops an internal boundary layer of sufficient height to affect measurements at the 11-m anemometer and produce vertically-heterogeneous behaviour. We describe the turbulence structure of the boundary layer, particularly the corresponding longitudinal integral scale of turbulence for different surfaces, while considering the effect of the internal boundary layer for the development of onshore flow. A methodology is developed to ensure independence from the internal boundary layer for onshore flow. The effect of stability on the integral longitudinal scale of turbulence is analyzed, revealing greater values for unstable atmospheric conditions. In stable atmospheric conditions, differences in surface roughness do not affect the turbulence structure for the anemometer studied.

Influence of the Arrangement of Surgical Light Axes on the Air Environment in Operating Rooms.

Purpose Surgical lights in the operating rooms are typically installed in a single axis in the center of the room or in two axes on both sides of the operating table. In the single-axis installation, the air-conditioning outlet cannot be placed in the center of the ceiling, which may affect the air current. Therefore, we measured the air current and cleanliness in two equivalent operating rooms using a vertical laminar airflow system equipped with either single-axis or double-axis surgical lights. Methods Air current was measured using a three-dimensional ultrasonic anemometer. Cleanliness was evaluated by measuring the amount of dust before and after air-conditioner activation. To visualize the air current, smoke was illuminated on a sheet of laser light while the air-conditioning was stopped, and changes after air-conditioning activation were observed. Results In the single-axis room, an oblique fast air current flowing from the surrounding air outlet toward the center was observed, and the flow velocity fluctuated greatly. In the double-axis room, uniform downward laminar airflow was observed. The amount of dust at the center decreased significantly faster in the double-axis room; thus, the cleanliness at the center was higher in the double-axis room. Persistent stagnation of smoke was observed below the single-axis lighting, whereas smoke below the double-axis lighting was immediately dispersed and the air cleared even when surgical lights were in the position for surgery. Conclusion Uniform vertical laminar airflow was formed and high cleanliness was achieved in the center of the room when the surgical lights were arranged in two axes.

Effects of Forced Air Warming on Airflow around the Operating Table.

Forced air warming systems are used to maintain body temperature during surgery. Benefits of forced air warming have been established, but the possibility that it may disturb the operating room environment and contribute to surgical site contamination is debated. The direction and speed of forced air warming airflow and the influence of laminar airflow in the operating room have not been reported. In one institutional operating room, we examined changes in airflow speed and direction from a lower-body forced air warming device with sterile drapes mimicking abdominal surgery or total knee arthroplasty, and effects of laminar airflow, using a three-dimensional ultrasonic anemometer. Airflow from forced air warming and effects of laminar airflow were visualized using special smoke and laser light. Forced air warming caused upward airflow (39 cm/s) in the patient head area and a unidirectional convection flow (9 to 14 cm/s) along the ceiling from head to foot. No convection flows were observed around the sides of the operating table. Downward laminar airflow of approximately 40 cm/s counteracted the upward airflow caused by forced air warming and formed downward airflow at 36 to 45 cm/s. Downward airflows (34 to 56 cm/s) flowing diagonally away from the operating table were detected at operating table height in both sides. Airflow caused by forced air warming is well counteracted by downward laminar airflow from the ceiling. Thus it would be less likely to cause surgical field contamination in the presence of sufficient laminar airflow.

Characteristics of Turbulent Airflow Deduced from Rapid Surface Thermal Fluctuations: An Infrared Surface Anemometer

The intermittent nature of turbulent airflow interacting with the surface is readily observable in fluctuations of the surface temperature resulting from the thermal imprints of eddies sweeping the surface. Rapid infrared thermography has recently been used to quantify characteristics of the near-surface turbulent airflow interacting with the evaporating surfaces. We aim to extend this technique by using single-point rapid infrared measurements to quantify properties of a turbulent flow, including surface exchange processes, with a view towards the development of an infrared surface anemometer. The parameters for the surface-eddy renewal (\(\alpha \) and \(\beta )\) are inferred from infrared measurements of a single-point on the surface of a heat plate placed in a wind tunnel with prescribed wind speeds and constant mean temperatures of the surface. Thermally-deduced parameters are in agreement with values obtained from standard three-dimensional ultrasonic anemometer measurements close to the plate surface (e.g., \(\alpha = 3\) and \(\beta = 1/26~\hbox {(ms)}^{-1}\) for the infrared, and \(\alpha = 3\) and \(\beta = 1/19~\hbox {(ms)}^{-1}\) for the sonic-anemometer measurements). The infrared-based turbulence parameters provide new insights into the role of surface temperature and buoyancy on the inherent characteristics of interacting eddies. The link between the eddy-spectrum shape parameter \(\alpha \) and the infrared window size representing the infrared field of view is investigated. The results resemble the effect of the sampling height above the ground in sonic anemometer measurements, which enables the detection of larger eddies with higher values of \(\alpha \). The physical basis and tests of the proposed method support the potential for remote quantification of the near-surface momentum field, as well as scalar-flux measurements in the immediate vicinity of the surface.

도시철도 차량 하부의 풍속 및 미세먼지 농도 특징

도시철도 차량의 운행은 터널 공기를 오염시키는 주된 원인이므로, 마모입자를 제거하는데 집진장치가 유용한 수단이 될 수 있다. 차량의 하부에 장착될 수 있는 집진장치의 설계조건을 파악하기 위하여 3차원 초음파 풍속계와 입자측정기를 사용하여 차량 하부의 풍속과 입자농도를 조사하였다. 2015년 2월 10일 수도권 지하철 5호선에서 운행되는 차량을 대상으로 측정하였다. 측정자료는 역 사이 노선의 형상(직선, 곡선)과 차량 속도패턴(가속, 정속 및 감속)을 구분하여 분석하였다. 차량속도도 함께 분석하였다. 직선 및 곡선 구간 모두 차량 하부의 평균 풍속은 차량속도의 약 30%이었고, 미세먼지(<TEX>$PM_{10}$</TEX>) 농도는 약 <TEX>$200{\mu}g/m^3$</TEX>이었다. 감속구간에서 평균 <TEX>$PM_{10}$</TEX> 농도는 가속구간에 비해 더 높았다. Since operation of railway trains is a major source of particle pollution in tunnel air, a particle removal device can be an effective measure to remove wear particles. To obtain design conditions of the particle removal device that will be installed underneath the railway trains, the wind speed and particle concentration underneath the trains were investigated using a three-dimensional ultrasonic anemometer and a DustTrak aerosol monitor, respectively. The measurements were made for the trains running on Seoul Metropolitan Subway Line 5 on February 10, 2015. The data were analyzed according to the track geometry (straight, curved) and train speed pattern (acceleration, cruising, and deceleration) between stations. Train speed was also analyzed. The average wind speed and <TEX>$PM_{10}$</TEX> concentration underneath the trains were ~30% of the train speed and <TEX>${\sim}200{\mu}g/m^3$</TEX> for both straight and curved sections. Average <TEX>$PM_{10}$</TEX> concentration for deceleration sections was higher than that for acceleration sections.

시분할 방식을 이용한 3차원 초음파 풍향풍속계 측정기술 개발

The three dimensional ultrasonic anemometer was constructed to reduce the disadvantages of the two-dimensional anemometer and to be free from the use environment. Three pairs of transmitting and receiving ultrasonic sensors were designed to face each other at an angle of <TEX>$45^{\circ}$</TEX> to the upper and lower surfaces at intervals of <TEX>$120^{\circ}$</TEX>. 200 kHz ultrasonic sensor Oscillation, transmission and reception, level detection, power supply circuit were designed and U, V, W wind speed vector components were obtained by measuring the time of first received ultrasonic pulse by transmitting pulse ultrasound. It is implemented as firmware in ARM Coretex-M3 processor so that horizontal and vertical wind direction and wind speed can be converted into digital signal by vector calculation. In this study, The three-dimensional ultrasonic anemometer can complement the disadvantages of the two-dimensional anemometer (mechanical and ultrasonic), and it is expected to gradually replace the two-dimensional anemometer due to its high utilization rate by collecting additional information such as vertical wind.

建築物近傍風観測における3次元超音波風速計の適用性に関する一考察

建築物近傍風観測における3次元超音波風速計の適用性に関する一考察

Field experiment and analysis of the wake behind a horizontal-axis wind turbine

Wind turbines work in a complex natural environment, where their flow field shows the characteristics of high turbulence levels. Due to the complexity and instability of the atmospheric boundary layer flow, as well as the influence of the scale effect, wind tunnel test cannot reflect the real working condition of wind turbine. So field experiments are very necessary to study wind turbine flow characteristics in actual wind field. In this investigation, field experiments of the wake behind a wind turbine were carried out to get velocity distribution in it. The field experiment system is composed of a 33 kW wind turbine, a 20 m high anemometer tower, a wake velocity measurement platform and the controlling device. The wind turbine is horizontal-axial, two-bladed, upwind-type, with variable pitch angles, 14.8 m in diameter. Wake velocity measurement platform is composed of an 18 m high hydraulic lift, anemometer installation platform and three sets of the US CSAT3 three-dimensional ultrasonic anemometer. Inflow parameters were gauged, such as wind speed, wind direction, atmospheric pressure, temperature and humidity. Besides, the operating conditions of the wind turbine were recorded, including pitch angle, yaw angle, rotor speed. It is discussed that the time domain and power spectrum characteristics of wake velocity at a measuring point located at one rotor diameter downwind from the rotor plane. The results show that there are larger velocity deficits in the wake. The axial velocity deficit rate at the measuring point is between 35.1% and 54.17%. The change of the velocity in vertical direction is small. The velocity in lateral direction is slightly larger than the velocity component of inflow, which reflects the expansion characteristics of the wake. Besides, the turbulent kinetic energy at the measuring point shows a periodic variation, and the vortex sheet passage frequency is similar to the rotation frequency of the wind turbine. Meanwhile, all of the power spectra of turbulent velocity in three directions at the measuring point show a characteristic of slope for –1 at the section of low frequency, which mean the turbulent flow is in the classical production subrange.

Numerical simulation of three-dimensional wind flow patterns over a star dune

In this paper, three-dimensional wind flow patterns over a star dune under a longitudinal (W, 270°) and transverse airflow (ENE, 70°) were examined using computational fluid dynamics (CFD) simulations. New surveying techniques of airborne LiDAR and DGPS allow for establishment of the realistic digital model of the star dune. Simulation results were then validated by field measurement using three-dimensional (3D) ultrasonic anemometers combined with arrays of HOBO cup anemometers. Results show that incident flow conditions (longitudinal or transverse airflow) controlled by the angle between incident flow and dune crestline exert great impact on wind flow patterns over the star dune. In periods of longitudinal airflow, a marked feature of wind flow pattern was flow deflection. Wind erosion occurs on both sides of WNW and S sides during W wind and its main effect was to prolong the star dune longitudinally. However, leeside flow separation and reversal were obvious under transverse airflow. The main effect of ENE wind was to promote the upward growth of the star dune. The CFD simulation of 3D wind flows over complex dune system presents great potential for geomorphological research, enabling new insights into complex dune geomorphology and dynamics.

Natural convection flows along a 16-storey high-rise building

The flow caused by natural convection adjacent to a heated vertical wall (wall flow) is an important mechanism in the creation of wind flows in a city when the background wind is weak. The wall flows along a 16-storey building were measured in Guangzhou, China. Fourteen three-dimensional ultrasonic anemometers were installed on three floors to study the boundary layer structure. Continuous measurements were taken during three test periods. The Rayleigh numbers were approximately 1013, 1013 and 1014 at the height of the 5th, 10th and 14th floors, respectively. The diurnal changes in the velocity of the wall flows, the wall surface temperature and the ambient air temperature were analysed.Our new experimental data support the theory that the natural convection boundary layer has a three-layer structure, i.e. an inner viscous layer, a transition layer and an outer turbulent layer, as first proposed theoretically by Wells and Worster. The outer turbulent layer is governed by the law of plumes with a Gaussian profile. The vertical velocity changes with g′4/9x1/3 along the vertical wall, where g′ is the buoyancy force and x is the coordinate along the vertical wall. It was noted that only the building's roof was significantly cooler than the ambient air at night, due to the sky radiation effect, so no downward flow adjacent to the wall caused by the cooling plate effect was found in our field measurements.