Spreading of Turbulent Warm/Cold Plane Air Jet in a Well Insulated Room

Project leader: Professor Bahram Moshfegh and Professor Mats Sandberg
PhD student: Shahnaz Amiri
Supported by: University of Gävle and KK-Foundation

KK-Fpundation logga

Introduction

People spend nearly 90% of their time indoors, at the home, at the office and during the transportation between them. Thus, it is very important to predict indoor environment in order to design healthy and thermally comfortable indoor spaces. The quality of indoor environments and thermal comfort of occupants is directly related to a number of parameters such as velocity of airflow, turbulence intensity and temperature distribution of room air. Thus the knowledge of the characteristics of the above-mentioned parameters is crucial for engineers to design an optimal ventilation system and for the researcher to improve the Computational Fluid Dynamics CFD codes.  

Turbulent wall jets are of considerable interest both for fundamental research and practical applications in the field of Heating, Ventilating and Air Conditioning. However, in spite of extensive previous research, major deficiencies in the knowledge and understanding of the flow and heat transfer field within the turbulent wall jets still exit. This situation is mainly due to two reasons, namely, the technical limitations of the measurements techniques and the currently available CFD codes are not validated or calibrated for indoor environment predictions. Furthermore there is a dearth of statistical data of the turbulence for the conditions valid for the propagation of the jet and room air flows. The availability of data is important for improvement of CFD codes in order to predict room air flows. To the best of my knowledge there are few results reported on the statistics of turbulence of non-isothermal flow at room air conditions.  

The present project is an ongoing research project which describes the experimental and numerical investigation of the propagation of turbulent warm and cold plane air jet under the influence of a heat sink or a heat source in an insulated room.

Keywords

 
Full-scale experiment, Numerical simulation, Plane air jet, Turbulent flow, Spectral analysis.

Summary of the presented papers

 

Paper I  
The intention of this paper is to present the flow and the thermal behaviour of the warm plane wall jet under the influence of a heat sink. Experimental results are carried out for air over a wide range of supply Archimedes numbers and Reynolds numbers. The velocity profile and temperature profile created within the warm air jet at different downstream locations from the supply are investigated experimentally. In addition, a number of correlations are presented between the normalised distance from the supply and the growth of the half-width of the air jet and the normalised decay rate of the maximum velocity.  

Paper II  
The paper reports the experimental results obtained for a warm plane air jet and includes some fundamental definitions of a turbulent flow field and spectral dynamics of turbulence. The flow conditions in a warm air wall jet are also summarised. In addition to the local maximum velocity, the turbulence intensity and the turbulence length scale, the properties of velocity fluctuations in terms of autocorrelation function and the spectral density are investigated experimentally and numerical treatment are presented. The experimental investigation is carried out for the warm plane air jet, spread horizontally from a slot under the ceiling in a well-insulated room where the floor is partly covered by a cooling panel.

Paper under preparation  

Paper III  
This paper deals with the numerical simulation of the air flow and heat transfer for the cases presented in Paper I and II. A steady three-dimensional model is considered to analyse the fluid flow and heat transfer in the full scale test room. The following assumption is also considered, thermophysical properties of the fluid are assumed to remain constant except for the buoyancy term of the momentum equation (ie the Boussinesq approximation). The radiation exchange between the radiation surfaces is included in the model. The governing equations, ie conservation of mass, momentum, energy, kinetic energy and dissipation of turbulent energy, are solved numerically. To solve the problem, the commercial finite element code FIDAP and a new two-layer turbulence model based on commercial code Phoenics are used for the simulation. The numerical results from paper III are compared by the experimental results obtained from Paper I and II.

Future work  

The following points are planned to be investigated in the coming future:
Detail experimental and numerical investigation of the thermal behaviour of a turbulent cold plane air jet under the influence of a heat source in an insulated room.

Large Eddy Simulation, LES, is also intended to be used as a computational tool for the flow and heat transfer within the room.

To use the Thermal Length as a new concept to analyse the thermal behaviour of the wall jets instead of the tradition way where the Archimedes number is used.   

Publications


1.   Amiri, S., Sandberg, M. and Moshfegh, B.(1996). Effect of Cooling Loads on Warm Plane Air Jet. Proceedings of The 5th International Conference on Air Distribution in Rooms, ROOMVENT '96. Yokohama, Japan.

2 .  S. Amiri, M. Sandberg and B. Moshfegh. (1998). Spectral Analysis of a Turbulent Warm Plane Air Jet (Using hot-wire anemometry).Proceedings of The 6th International Conference on Air Distribution in Rooms, ROOMVENT '98, Stockholm, Sweden.

Publicerad av: Liselotte Laurila Sidansvarig: Gunilla Mårtensson Sidan uppdaterades: 2013-10-17
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