[in Japanese]

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The 2-D rectangular cross section with corner-cut in each edge has been accepted as one of the effective aerodynamic stabilizing countermeasure. Previous wind tunnel experiments proved that vibrational amplitude as well as stationary aerodynamic force such as draf force, lift force could be remarkably reduced by this slight geometrical change. However, it is recently reported that the aerodynamic properties are so sensitive to Reynolds number. Intensive investigation including a couple of committee works have been then initiated in civil engineering field . The dependence on Reynolds number and its mechanism are introduced in this paper based on these activities.

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The effect of Reynolds number on 2-D elliptical cylinder, with slenderness ratio of 3, is briefly investigated from the both of stationary forces and aerodynamic damping characteristics points of view. This cylinder is, in conclusion, less affected by Reynolds number over than Re=1. 4x 104 (Re= UD/v, D: height of cylinder), approximately.

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High accuracy and reliability of measured data in wind tunnel tests at developing aircraft are strongly need due to economical reasons. Some Examples of Reynolds number effects, wind tunnel wall intereference, sting interference, engine installation effects and flow quality effects are outlined. They all affect strongly on the ability of the wind tunnel simulation in aeronautics . The need of a high Reynolds number wind tunnel in Japan is pointed out.

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The similarity requirements for wind tunnel model studies of buoyant and heavy gases diffusion near buildings are presented and discussed. Exact similarity of buoyant and heavy gases behavior requires explicit scaling of the released gas density and equality of the model and full scale Froude numbers. The latter requirement leads to very low wind speeds for wind tunnel tests when small scale models are used. This condition makes the physical modeling of flow and diffusion fields complicated and thus reliable wind tunnel operation becomes very difficult. Approximate modelling methods, which relax the requirement of gas density scaling in order to operate at higher wind tunnel speeds, are also examined.

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Flow characteristics of a rectangular cylinder with a side ratio of 1 to 6 were experimentally investigated with hot-wire techniques at Reynolds numbers of (0.2-1.5) ×10⁴. Especially, meta-stable flow patterns which have different modes are found to appear in the wake of the cylinder with the side ratio of 2.3 to 3. The phenomenon is dependent on the Reynolds number and the side ratio. The conspicuous difference of the flow patterns of each mode can be certified by both spatial distribution and temporal evolution of spectrum intensity of fluctuating velocity in the wake, which are measured by a short-time spectral estimation of the maximum entropy method (MEM), i.e. a stochastic appearance of the flow pattern of each mode and a coexistence of two mode-patterns. Next, aerostatic characteristics of structural angle section (L-shaped section) were studied in a wind tunnel. Lift and drag forces, moment and Strouhal numbers were measured against the angle of attack . It is found that aerostatic characteristics of L-shaped section are very similar to those of T-shaped section at the corresponding angles rotating 45 degree.

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The wind resistant design against the wind induced vibration has based on the sectional model wind test, while some examples of the full bridge model wind tests have been carried out in order to verify safety of the target structure and its sectional model test result. In this process main topics in the testing technique are always the relationships or interpretation among these two methods. In this paper this discussion will be summarized and the re cent coupled flutter analysis will be introduced from a viewpoint of the method interpretation.

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This paper describes the flutter property of elastic system with multiple modes based on a conventional modal complex eigen-value analysis. The flutter is, in conclusion, almost covered by a fundamental lowest-mode combination of heaving and torsional modes even though the target mode of flutter seems to be a higher mode than the lowest one.

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The strip theory approximation that assumes 2-dimensionally fluctuating wind velocity field to obtain the buffeting forces on a bridge cross-section has been used in the conventional buffeting analysis . Because the actual wind velocity varies along the bridge span and the flow over the neighbour sections has effects on the aerodynamic forces, the strip theory' approximation does not strictly hold . In this study, the actual buffeting force distribution on a model with flat hexagonal cross-section was measured and compared with the analytical result by the strip theory approximation. There were some differences and the effects of these differences on the prediction of the bridge buffeting responses are discussed .

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The yaw angle effects of wind on the vortex induced oscillation of a rectangular cylinder (the width/depth ratio.B/D=2.5) was investigated by wind tunnel tests with two dimensional rigid model and taut strip model. Strong oscillations were observed under various yaw angles.The end conditions had little effect on the response and the Karman vortex in the wake seemed to have a different roll on the responses of models in normal incidence and in yaw angle.

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This paper describes an experimental study of the vortex induced vibration of tapered cylinders which is being used for the tower. In the experiment, effects of turbulence, structural damping and taper were investigated. From the investigation, the following results were obtained.
1. The vortex induced vibration occurs for any types of cylinders from a straight cylinder and afull tapered cylinder when the structural damping is small enough both in smooth and turbulent boundary layer flows.
2. The tapered part does not effect so much on the vortex induced vibration when the tapered part is less than a half of the cylinder height, but the onset velocity of the vibration shifts to the higher velocity and the velocity rage of the vibration becomes wider when the tapered part is beyond 3/4 of the height.
3. The response is much larger at the higher wind velocity in the turbulent flow than in the smooth flow when the tapered part is beyond 3/4 of the height.

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This paper introduces the aerodynamic device utilizing three dimensional aerodynamic characteristics of the pylon, to suppress the wind-induced vibrations in the cable-stayed bridge pylon. The pylon form is assumed to be “A” which includes “inverse Y” and “inverse V”. The pylon often vibrates in the perpendicular direction to the bridge-axis by the bridge axis wind. The corner-cut is said to be effective in stabilizing the aerodynamic characteristics of a pylon section . It can be seen that the application of a corner-cut to a half length of the upper shaft is more effective than to the full length of the upper shaft. The horizontal beam connecting two upper shafts in “A” pylon is also effective to suppress the wind-induced vibrations. The stream visualization with a taft method shows that the horizontal beam in “A” pylon disturbs the axial flow along the shaft side-face which is a strong current in the “inverse V” pylon.

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It has been said that the aerodynamic stability of an entire 3-dimensional structure can be estimated by integrating the aerodynamic stability of its 2 -dimensional cross section (Strip Theory). The author conducted this time a series of wind tunnel tests on 2- and 3-dimensional scale models representing a long-span box girder bridge and compared the test results with what were obtained theoretically by Strip Theory . Consequently it was found that Strip Theory would not necessarilly hold true when applied in predicting the aerodyn amic stability of such a long-span box girder bridge whose cross section varies in its longitudinal direction.

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The aerodynamic device on suspension bridge tower standing isolatedly during construction is investigated in order to suppress the vortex-induced oscillation. The plate attached on both wandward and leeward surface of two tandem tower columns effectively stabilizes the structure. It is known that the optimum install length and location of the device along the column is only 10% of tower height at the crest of tower. It proves that the aerodynamic 3-D effect near the crest is controlling the whole response characteristics of tower.

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This report describes the trend and problems for the summarized examples of full scale measurements which have recently been carried out in the structural wind engineering divison. The aim of the report is to furnish topics of conversation in a panel discussion. Data of the Reynolds' effect, appropriate evaluation period for a fluctuating response and the evaluation of structural damping can not satisfactorily be determined from wind tunnel tests . The importance of actual measurements is placed not only on how to gather data which is difficult to be obtained from wind tunnel tests, but on the comparison with the results of wind tunnel tests.

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As far as an actual automobile is put into the test section of a fairly large wind tunnel, there are little problems in the wind tunnel testing of the automobile. That is because three major problems in the wind tunnel, that is, the Reynolds number effect, the wall interference and the balance support interference are easily overcome. The biggest remaining problem is the ground simulation, which simulates the relative motion between the vehicle body, the rotating wheels and the ground. The moving belt technique, one of the ground simulation methods, is briefly described in this paper. The experimental results show that the ground simulation of some kind is necessary even in case of usual passenger cars.

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The wind velocity of the overturning of a vehicle due to cross-winds depends on the aerodynamic characteristics of the vehicle on the ground, an embankment or a bridge. The field tests were made on the aerodynamic characteristics of the vehicle at rest on the bridge and the wind tunnel tests corresponding to the field tests were also made. The results of the wind tunnel tests agreed with those of the field tests qualitatively.

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Results from a field study of the flow-induced vibrations of a full-scale, long-span, shell-type gate undergoing simultaneous over- and underflow are presented.Data include experimentally determined mode shapes and frequencies for both horizontal and vertical bending modes, the maximum center-span vibration amplitudesin the horizontal and vertical direction as functions of underftow gate openings and overflow depths, and the trajectories of gate motion. Predictions of gate vibration, based on theories previously developed from model-scale data, were in good agreement with the experimentally observed behavior. Several subjects for future study are also presented in this study.

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Wind tunnel is one of the good tool for the research of mechanism, simulation ofairflow and pollutant diffusion in the atmosphere. Particulary, for the simulation of airflow around buildings or topography, wind tunnel is the most reliable tool . In this paper present state of the wind tunnel simulation of airflow and diffusion is discussed with several simulation studies of airflow and diffusion in adiabatic boundary layer, in a street canyon, diffusion from a source on a building roof and airflow over an isolated mountain

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Wind tunnel experimental conditions of simulating atmospheric turbulence over complex terrains were examined by comparison with the observed data. The similar ity conditions are found that (1) the vertical wind distribution is set to be similar to the field one, (2) the Reynolds number is set larger than 4×10⁴. Wind tunnel spectra agreed well with the field ones with nondimensional frequency.

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A three-dimensional non-hydrostatic anelastic model using a radiative-nesting lateral boundary condition is applied to the simulation of the Yamaji-kaze on 27 September 1991 caused by the Typhoon 9119. A 2.5 km-resolution model, which is double-nested with the operational forecast model of the Japan Meteorological Agency, successfully simulates the downslope wind and associated internal hydraulic jump in the lee of the Shikoku Mountains. The model-simulated wind reproduces well the time change of the observed wind, including the abrupt increase of the southerly wind (onset of the Yamaji-kaze).

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Similarity in the dynamics of the tornado vortices between nature and laboratory experiments is discussed based on the flow visualization in the guide vane type simulator. Structure and dynamics of the tornado vortices in the experiment are found to depend on the Reynolds number and the swirl ratio of the inflow.

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