Jon A. Peterka

Wind flow patterns about buildings

Abstract A knowledge of building wake characteristics is useful in a variety of applications including dispersion of pollutants downwind of conventional or nuclear power plants, airport runway interference effect, take-off/landing limitations at heliports, pedestrian wind comfort, and wind loads on structures. Recent investigations have advanced both understanding of physical flow processes occurring in the near and far wake regions and theoretical predictive capability for flow and diffusion in the far wake region. These studies have shown, for example, that separation cavities immediately downwind are not enclosed by free streamlines as in two-dimensional separation/reattachment, that organized vortices can play an important role in wake development, and that theoretical solutions for some wake regions are possible.

Selection of local peak pressure coefficients for wind tunnel studies of buildings

Abstract It has been recognized that the probability distribution of the largest peak pressure achieved during a design storm at a particular location on a building is skewed with a long tail extending toward higher loadings. Several procedures have been suggested in the literature for determining the statistical characteristics of the peak pressure. This paper provides an optimized method for prediction of the peak pressure from wind-tunnel model studies.

Improved extreme wind prediction for the United States

Abstract An investigation of sampling error due to short data records was investigated for the fastest mile of wind records used to form design wind speeds for the U.S. The data for 29 stations in the midwest were checked for statistical independence and for trend over the geographical area. A superstation was formed from the stations containing 924 station-years of record, and 10,000 years of record with the same Type I distribution were generated by random function generator. The simulated data was shown to have the same distribution of predicted 50-years speeds, if divided into 25-year long records, as occurred for the 29 real stations. The analysis showed that the major variation in predicted 50-year wind speed from station to station is the sampling error. It also showed a method for effectively removing most of the sampling error.

Wall pressures of separation—reattachment flow on a square prism in uniform flow

Abstract Mean and fluctuating pressures on a two-dimensional square prism in uniform flow at a Reynolds number of 1.4 × 10 5 were measured to investigate the nature of the separation—reattachment phenomenon. Measurements were taken on the side-wall face and in the wake region to quantify the behavior of the fluid in the reattachment zone. The experiment was performed with and without a turbulence producing grid for angles of approach flow ranging from −50° to +90°.

Mean force and moment coefficients for buildings in turbulent boundary layers

Abstract Mean force and moment coefficients for a series of flat-roofed rectangular buildings are presented for a range of wind directions. The coefficients were determined by integrating mean pressures measured on model structures immersed in thick turbulent boundary layers simulating four typical neutral atmospheric flow conditions (power-law exponents of 0.12, 0.27, 0.34, and 0.38). A series of thirteen different building geometries were studied. The ratios of adjacent sides were 1, 0.5, 0.25, and the aspect ratio, the ratio of the height to the smaller side, ranged from 1 to 8. The effects of side ratio, aspect ratio, incident turbulence intensity, longitudinal integral scale, and the ratio of building height to boundary-layer thickness are discussed.

Comparison of pedestrian wind acceptability criteria

Several pedestrian wind comfort criteria have been suggested to help city planners and architects evaluate the safety and comfort of locations around planned developments. The criteria are based on the percent time certain wind speeds are exceeded annually but differ in implementation. To describe the relative behavior of the criteria, wind tunnel measurements of pedestrian wind speeds for nine building projects have been evaluated against five criteria: Melbourne (1978), Hunt, et.al. (1976), Penwarden and Wise (1975), Lawson and Penwarden (1975), and Isyumov and Davenport (1975). Measurements were made for 246 locations and were compared to the criteria. Differences among the criteria are evident, with that of Melbourne (1978) being more restrictive than those of Lawson and Penwarden (1975) and of Isyumov and Davenport (1975). Elevated turbulence intensities found near high-rise structures and the differing usage of mean and peak winds partially account for the differences.

AVERAGED PRESSURE COEFFICIENTS FOR RECTANGULAR BUILDINGS

Mean pressures obtained from an extensive series of wind-tunnel tests have been averaged over an entire side of a building to obtain a single mean pressure coefficient for a given side and wind direction. Coefficients based on either a local reference wind speed or a reference wind speed measured at the level of the roof of the building have been computed. An example and a comparison with existing building codes and standards are included to illustrate the use of these coefficients.

Mean and Peak Wind Loads on Heliostats

Mean and peak wind loads on flat rectangular or circular heliostats were measured on models in a boundary layer wind tunnel which included an atmospheric surface layer simulation. Horizontal and vertical forces, moments about horizontal axes at the ground level and at the centerline of the heliostat, and the moment about the vertical axis through the heliostat center were measured. Results showed that loads are higher than predicted from results obtained in a uniform, low-turbulence flow due to the presence of turbulence. Reduced wind loads were demonstrated for heliostats within a field of heliostats and upper bound curves were developed to provide preliminary design coefficients.

SECONDARY FLOWS AND VORTEX FORMATION AROUND A CIRCULAR CYLINDER IN CONSTANT-SHEAR FLOW

A pair of curved gauzes with non-uniform porosity was used to generate a strong constant-shear flow with low turbulence intensity. The complex features of this flow around a circular cylinder with its axis normal to the vorticity and mean velocity vectors were studied. Methods such as the use of end plates, inclusion of gaps at the junctions of the cylinder with the end plates and fluid withdrawal were applied to minimise end effects. Exploratory studies were made to investigate shear effects on the vortex wake formation region. Effects of the steepness factor on vortex formation were explained.

Computer simulation of non-Gaussian multiple wind pressure time series

The paper presents a technique for generating artificial multiple wind pressure time series with strong cross correlations in fluctuating features. The technique, for given multiple target time series, simulates an identical shape of sample auto- and cross-spectra of target signals in records of calculated artificial signals and has great flexibility in controlling non-Gaussian distributional properties while preserving the auto- and cross-spectra. The technique utilizes the unique properties of the Fourier phases in Fourier representation of time series in connection to non-Gaussian fluctuating feature generation and the phase shift relations in connection to simulating cross correlations of multiple target signals.