turbulence

The authors introduce a new airflow characteristic, the equivalent frequency, as an integral measure for the frequency of the random velocity fluctuations in rooms. The aim of that study was to test the impact of the equivalent frequency on draught sensation for human subjects. Further investigation at different air temperatures along with different turbulence intensities of air velocity is recommended.

This paper deals with low Reynolds number jets for personalised ventilation and the possibility to control them in order to obtain useful modifications of the flow field, it can be done by simply adding a ring-like perturbation in front of the jet itself.

The paper presents the results of the measurement of turbulence intensity in jets issued into enclosures of different size. The test results confirm the relation between the velocity distribution coefficient and turbulence parameters.

The estimate of actual air change rates considering atmospheric turbulence isintroduced. The starting point is the spectral description of turbulence - Kaimalspectrum was used in order to consider the height above ground. A set of syntheticwind velocity series are generated, out from a modified spectrum. The procedureconsiders an aerodynamic transfer function (a filter) where peculiar and cut-offfrequencies are determined by the general dimensions of the building and of theexternal openings, i. e., the turbulent scales of interest.

To ensure prompt response by real-time air monitors to an accidental release of toxic aerosols in a workplace, safety professionals should understand airflow patterns. This understanding can be achieved with validated computational fluid dynamics (CFO) computer simulations, or with experimental techniques, such as measurements with smoke, neutrally buoyant markers, trace gases, or trace aerosol particles. As a supplementary technique to quantify airflows, the use of a state-of the art, three-dimensional sonic anemometer was explored.

In order to estimate air change rates (ACH) on Natural Ventilation (NV) processes a number of factors should be known as general and openings dimensions, pressure distribution over the facades, internal heat sources (or sinks) and head losses. The atmospheric boundary layer (ABL) characteristics change with the terrain roughness and affect the pressure distribution. Construction features determine infiltration rates, flow regimes through openings and its head losses so affecting the internal airflow.

The overall objective of the present work is to evaluate the performance of three turbulence models, with a view to predicting characteristics of airflow within an anisothermic cavity. The standard K-c. model, the Renormalisation Group model (RNG) and the Reynolds stress model (RSM) are used in conjunction with the Fluent code. The accuracy and the relative performance of the three models are evaluated by comparing their numerical results with experimentally obtained data. This comparison is made for the constant flow rate of a twodimensional turbulent mixed convective airflow.

Forced air circulation in a storage room either with freezing/cooling or controlled atmosphere is usually turbulent because a high air change rate is generally required. The interaction between the turbulent air flow and the product layers plays an important role in the performance of the storage room. In this paper, a homogenous model based on the Brinkman-Forchheimer-extended Darcy equation for both fluid and porous layer is described, in association with the standard k-e turbulence model.