Peter Stankov

Integrating CFD and building simulation

Abstract To provide practitioners with the means to tackle problems related to poor indoor environments, building simulation and computational fluid dynamics can usefully be integrated within a single computational framework. This paper describes the outcomes from a research project sponsored by the European Commission, which furthered the CFD modelling aspects of the ESP-r system. The paper summarises the form of the CFD model, describes the method used to integrate the thermal and flow domains and reports the outcome from an empirical validation exercise.

CFD based study of thermal sensation of occupants using thermophysiological model. Part I: Mathematical model, implementation and simulation of the room air flow effect

Purpose – The purpose of the paper is to simulate the effect of clothing insulation and activity on the interaction between the human body and the environment. Design/methodology/approach – A thermo-physiological model, integrated into a Fluent CFD software package is applied. The temperature of the skin surface, clothing surface and heat flux (dry and total heat flux) through layers of clothing with different insulation level are numerically investigated in function of the clothing insulation and the different activities performed indoors. Findings – The increase of the clothing insulation leads to increase of both skin and clothing temperature. Higher temperature difference ΔT between the room temperature and skin temperature provokes more dynamic change of the skin temperature and decreases the thermal comfort of the person. The increase of the metabolic rate, however, leads to more uniform skin temperature, regardless the temperature difference ΔT. With the increase of the clothing insulation for a co...

Computational modeling and experimental validation of the air permeability of woven structures on the basis of simulation of jet systems

The paper presents computational fluid dynamics-based numerical simulation of the through-thickness air permeability of woven structures, applying the theory of jet systems. The flow through the interstices between the warp and weft threads is modeled as an “in-corridor”-ordered jet system, formed by nine jets, issuing from nine pores of the woven structure. Fifteen cases were simulated and three different turbulence models were applied in the simulation: k-ɛ, k-ω and Reynolds stress model. The five simulated woven structures were manufactured and their air permeability was measured experimentally. The performed validation of the numerical results with the experimental values of the air permeability showed very good correlation with the experimental results. The analysis and the verification showed that the method can be applied for further investigation not only of the woven fabrics’ air permeability, but also for investigation of the flow after a textile barrier of a woven type.

Three dimensional simulation of air permeability of single layer woven structures

The paper deals with a CFD based study of the transverse permeability of a textile woven structure. The reported numerical investigation is preconditioned by both previous experimental and CFD study on jet systems. It is also based on detailed experimental investigation of the porous structure of single layer woven fabrics, made of staple fiber yarns. The flow in through-thickness direction of the woven structures is presented as jet systems, issuing from set of orifices. Two different types of jet system (3×3 jets and 5×5 jets) with two types of jet cross sections (square and circular), corresponding to two different woven structures, are simulated. An analysis is made in terms of the structure of the woven fabrics (area and shape of the interstices between the threads), the parameters of the flow passing through the textile (velocity profiles and velocity fields through isosurfaces), the role of the type of the jet systems, representing the flow and the influence of the shape of the interstices between the threads on the flow pattern. It was found that the applied approach could be effectively used for studying of the transverse permeability of the woven fabrics.

CFD based study of thermal sensation of occupants using thermophysiological model. Part II

Purpose – The purpose of the paper is to simulate the effect of clothing insulation and activity on the interaction between the human body and the environment. Design/methodology/approach – A thermo-physiological model, integrated into a Fluent CFD software package is applied. The temperature of the skin surface, clothing surface and heat flux (dry and total heat flux) through layers of clothing with different insulation level are numerically investigated in function of the clothing insulation and the different activities performed indoors. Findings – The increase of the clothing insulation leads to increase of both skin and clothing temperature. Higher temperature difference ΔT between the room temperature and skin temperature provokes more dynamic change of the skin temperature and decreases the thermal comfort of the person. The increase of the metabolic rate, however, leads to more uniform skin temperature, regardless the temperature difference ΔT. With the increase of the clothing insulation for a constant metabolic rate the total heat flux remains constant, but the dry heat flux decreases, while the evaporative heat flux increases. Originality/value – The joint influence of clothing insulation and indoor activities on the thermal interaction between the body and the environment is assesses using a thermo-physiological model, integrated in a CFD software package.

Numerical modeling of the air permeability of two-layer woven structure ensembles

This study aims at investigating air permeability in the transversal direction of pairs of woven textiles. Three samples of woven macrostructures with different characteristics are selected for the numerical investigation of 16 two-layer ensembles. Computational fluid dynamics (Reynolds-averaged Navier–Stokes equations) is used for modeling the air permeability, applying the theory of jet-systems: the flow through each of the layers in the ensemble is modeled as an “in-corridor” ordered jet-system. The influence of the order of arrangement of the layers in the ensemble is analyzed, indicating higher air permeability of the ensemble when a tighter structure is placed as a first layer. The effect of the distance between the two woven macrostructures is also analyzed, showing a strong influence on the flow development as well as on the extrema of flow velocities, especially in the drop of the flow velocity in the air gap between the two layers. The analysis made and the results obtained show that the method can be applied for further investigation of ensembles of textile layers.

Numerical Study of the Effect of a Natural Convective Boundary Layer around the Human Body on the Transfer of Heat through a Textile Structure

Heat losses from the human body occur through a barrier of one or more textile layers with particular permeability, thermal insulation, water absorption abilities, etc. The convective boundary layer (CBL) around the clothed body is disturbed during body movement, and the air layer between the body and the textile layer(s) is broken up, thus changing the heat transfer through the textile layer and its insulation abilities. The purpose of the present study was to evaluate the effect of the convective boundary layer around the human body on the heat transfer through a textile layer by numerical simulation, using Computational Fluid Dynamics and a commercial CFD software package, by means of the Finite Volume Method. A new approach for modeling a textile surface was applied based on the theory of jet systems. The results of the study indicated that heat transfer trough the textile barrier is strongly influenced by the speed of the convective layer around the human body and the textile layer placed in between the body and the environment.

Integration of thermophysiological body model in CFD

A two-node mathematical model of the human thermophysiological system has been integrated into a Computational Fluid Dynamic (CFD) simulation of the airflow in a room. Temperature inputs from the CFD are used by the model to evaluate the dry and latent heat flux from the body surface and output them as boundary conditions. This is an iterative process and convergence is ensured by under-relaxation of the latent heat flux. The model also considers the dry and latent heat resistance of clothing. Numerical predictions of the body heat loss and airflow are compared against physical measurements in a climate chamber. Good agreement was observed when using the low Reynolds number turbulence model. The integrated simulation performs well under wide set of conditions, predicting body core and skin temperature, blood flow, skin wittedness, as well as the transfer of heat and moisture released by the body into the room.

Computer Simulation of the Air Flow and the Distribution of Combustion Generated Pollutants around Buildings

The paper presents numerical results from a computer simulation of the flow and flue gas distribution around a building complex. The buildingcomplex simulated consists of six buildings with different heights and shapes. The source of flue gas is a chimney of a local heat generation unit equipped with a 45 [MW] hot water boiler firing natural gas. Two cases which differ in the height of the chimney are studied: in the first case the chimney has a height of 40 [m] above the ground level and in the second - a height of 48 [m]. It is shown that the plume reaches one of the buildings in the site. Although it was found that for the conditions specified in the present study there is no hazardous concentration of any of the pollutants in the flue gas around the building, the situation could easily change, especially for the case with the lower chimney - e.g., when a stronger wind appears.

Numerical investigation of the heat transfer through woven textiles by the jet system theory

Abstract The paper presents a numerical study on the heat transfer in through-thickness direction of single woven layers, based on the jet system theory. A mathematical model, involving the Reynolds-Averaged Navier-Stokes partial differential equations is used, and two turbulence models (k − ɛ and RSM) are applied to solve the closure problem. Numerical results for the temperature distribution, heat rate, heat flux and thermal resistance of the samples are obtained, analyzed, and validated by experimental data. The presented approach for modeling the heat transfer through woven macrostructures is concluded to be a working numerical tool that has the potential to replace costly design iterations and experiments to produce woven textiles with desired performance.