Animal Occupied Zone Research Articles

A Multi-Airspace Model to Investigate Airflow Patterns and Carbon Dioxide Emission Sources in Deep-pit Beef Cattle Finishing Facilities

HighlightsA multi-control volume mass balance approach tested with data from cattle finishing barns.Airflow estimates were highest in the barn airspace, compared to the animal-occupied zone and manure pit headspace.Slurry CO2 emission calculations were sensitive to gas concentration differences between zones and animal numbers.Abstract. An increasing number of cattle finishing barns in the Midwest are naturally ventilated (NV) with slatted floors over deep-pit manure storages. However, there is limited gas emission data currently available for this type of cattle housing and manure storage. Emission rate measurements are particularly challenging in NV barns where there are low gas concentrations and large variations in air velocity and direction. This research explores gas emission estimation using carbon dioxide (CO2) concentrations measured at the north and south wall openings, floor, nose level, and above the manure surface in the storage pit. With these measurements, three control volume mass balances for the barn airspace, animal-occupied zone (AOZ), and manure pit headspace were used to estimate airflows between control volumes and CO2 emissions rates. In this study, the estimated airflow and CO2 emission values for two NV barns were calculated for the summer, fall, and spring seasons. Nominal airflow rates calculated between the three control volumes for each barn were variable using three different solution approaches applied in this study. There was a general pattern where airflow through the barn airspace was larger than airflow between the barn airspace and animal-occupied zone, followed by airflow through the slatted floors. The range of estimated CO2 emissions considering both barns and three solution approaches was -1.16 g/s to 29.3 g/s. Overall, while calculated airflow and CO2 emission results were variable across three solution approaches, this study provides insight on a range of CO2 emissions and airflow rates through deep-pit NV cattle finishing facilities. Further model validation would be needed prior to the use of this model for gas mitigation purposes. Keywords: Airflow, Beef cattle, Carbon dioxide emission, Deep-pit barns, Modeling.

Airflow characteristics of attachment ventilation in a nursery pig house under heating mode

In the current energy saving context, it is important to study the airflow that regulates the environment of an animal-occupied zone (AOZ) and reduces the heating load of the barn in a nursery pig house. Forced convection heating regulates the overall thermal environment in a nursery barn using hot air while reducing the pollutant concentration. This improves air quality and has energy-saving attributes. In this study, we investigated a pen-attached ventilation (PAV) airflow system in a nursery pig house based on the hot air heating method during winter. The air distribution, temperature field diffusion characteristics, and ventilation effectiveness of the PAV were investigated using a full-scale test bench and computational fluid dynamics (CFD) during the heating mode. The results show that PAV can effectively deliver fresh air and heat to the lying area of nursery pigs, as well as reduce the vertical temperature stratification inside the pig house. In addition, the average temperature in the lying area increased by 3.77 °C, the energy utilization coefficient increased by 0.2, and the energy saving rate was 12.7% when compared to the mixing ventilation (MV) airflow regulation mode for the same heat input. The PAV airflow approach reduced the energy consumption in the operation stage of the barn and theoretically justified its application to the thermal regulation of the environment of nursery pigs. • We investigated a PAV airflow system for the hot air heating method. • The average pig house temperature increased by 3.77 °C with this method. • This method reduced energy consumption in the operation stage of the barn by 12.7%.

Full-scale CFD simulation of commercial pig building and comparison with porous media approximation of animal occupied zone

Many CFD simulation studies substitute Animal Occupied Zone (AOZ) as porous media to reduce computation time and resources. With the improved computational capacity, it is now possible to include realistic geometric models of individual animals and partition walls. This study presents a CFD model of a large commercial-sized, hybrid ventilated pig building with 1,360 animals. It compares the developed full-scale model (that includes pigs and partition walls) with a simplified model that substitutes AOZ with a porous media approximation. We find that the simplified model with porous media approximation predicts the airflow rates and overall flow characteristics in the building as good as the full-scale model. Full-scale simulations with animals and partition walls give a snapshot of a particular situation in the building and the environmental conditions in the AOZ level; for example, we found that even in a well-ventilated pig building temperatures in the AOZ were, on average, 3 °C - 5 °C higher than at a height 0.5 m above the AOZ. Including the realistic shape of animals and the partition walls is overkill if the aim is to study ventilation configurations’ effects. However, porous media models are not good enough to describe the conditions in the AOZ.

Modelling of animal occupied zones in CFD

Methods to model animal occupied zones in computational fluid dynamics (CFD) for predictions of air properties are explored. The study was based on CFD analysis supported by experimental validation. Animal occupied zone (AOZ) are modelled as a porous media to reduce the computational cost. Here, the porous media was modelled in two ways. The first with constant and uniform values of porous-resistance coefficients throughout AOZ and called the porous-media method (POM), and the second with porous resistance considered according to the spatial location of the occupants and called profiled-porous-media method (PPOM). For POM, a CFD sub-study was required to estimate the porous media resistance coefficients. For PPOM, porous resistances were considered as infinite at the spatial-locations of occupants but elsewhere the resistance was zero – no separate study for estimating resistance coefficients were required. Results of the simulations with both POM and PPOM were compared with the CFD simulations when animals were present in AOZ. It was concluded that it is possible to model AOZ as a POM or PPOM. However, in POM, the coefficients of porous-media were layout dependent and a separate study for estimation of porous-media coefficients will always be required for each single layout. Moreover, POM under-predicted the average velocities in AOZ. On the other hand, there were two benefits of PPOM. Firstly, no separate study was required for the estimation of porous coefficients and the secondly it gave more realistic average velocities in the AOZ. Average temperatures in AOZ were accurately predicted by both POM and PPOM.

CFD modelling of an animal occupied zone using an anisotropic porous medium model with velocity depended resistance parameters

The airflow in dairy barns is affected by many factors, such as the barn’s geometry, weather conditions, configurations of the openings, cows acting as heat sources, flow obstacles, etc. Computational fluids dynamics (CFD) has the advantages of providing detailed airflow information and allowing fully-controlled boundary conditions, and therefore is widely used in livestock building research. However, due to the limited computing power, numerous animals are difficult to be designed in detail. Consequently, there is the need to develop and use smart numerical models in order to reduce the computing power needed while at the same time keeping a comparable level of accuracy.In this work the porous medium modeling is considered to solve this problem using Ansys Fluent. A comparison between an animal occupied zone (AOZ) filled with randomly arranged 22 simplified cows’ geometry model (CM) and the porous medium model (PMM) of it, was made. Anisotropic behavior of the PMM was implemented in the porous modeling to account for turbulence influences. The velocity at the inlet of the domain has been varied from 0.1 m s−1 to 3 m s−1 and the temperature difference between the animals and the incoming air was set at 20 K. Leading to Richardson numbers Ri corresponding to the three types of heat transfer convection, i.e. natural, mixed and forced convection. It has been found that the difference between two models (the cow geometry model and the PMM) was around 2% for the pressure drop and less than 6% for the convective heat transfer. Further the usefulness of parametrized PMM with a velocity adaptive pressure drop and heat transfer coefficient is shown by velocity field validation of an on-farm measurement.

Numerical Simulation of the Placement of Exhaust Fans in a Tunnel-Ventilated Layer House During the Fall

HighlightsThe placement and operation of exhaust fans was assessed using CFD simulation.The effective temperature was used to evaluate the indoor thermal environment.The placement and operation of the exhaust fans mainly affected the airflow patterns in the part of the layer house closest to the fans.Abstract. The thermal environment inside a layer house significantly affects the growth, production, and health of the hens. Tunnel ventilation systems have been widely applied to control the indoor climate and air quality for large-scale poultry facilities around the world. Generally, only a few of the exhaust fans operate during mild seasons (spring and fall) in a tunnel-ventilated layer house depending on the outside air temperature. The decision about which exhaust fans to turn on affects the indoor airflow pattern and temperature distribution. However, little research has been reported that investigated the effects of the locations of exhaust fans on ventilation performance. In this study, a computational fluid dynamics (CFD) model was built and validated using field-measured data. The CFD model was then used to evaluate different ventilation strategies (combinations of exhaust fans) in a typical tunnel-ventilated layer house during the fall. The effective temperature was used to assess the performance of different ventilation strategies. Results showed that the locations of the exhaust fans significantly affected the indoor thermal environment, especially in the part of the house closest to the fans, because different locations of operating fans can generate different airflow patterns and affect the airflow through the animal-occupied zone. Based on the simulations, we conclude that the placement and operation of the exhaust fans can be optimized. Turning on the fans that are lower to the ground or near the sidewalls will result in more air bypassing the animal-occupied zones. Our results can help select the best ventilation strategy during the spring and fall in layer houses with tunnel ventilation systems. Keywords: Airflow distribution, Effective temperature distribution, Indoor thermal environments, Ventilation strategy.

Temperature distribution in a finisher pig building with hybrid ventilation

The differences between temperatures in the animal occupied zone (AOZ) and temperatures measured by control system sensors are rarely explored. This experimental study quantifies the dry-bulb air temperature [hereinafter temperature] distribution inside a finisher pig building that combines natural ventilation through automatically controlled openings with a mechanical ventilation system. Year-long temperature data from 28 sensors located at 3 different heights in the building was analysed to help understand the temperature distributions and indicate the temperatures below or above an assumed optimal temperature range, defined as between 14 °C and 24 °C. Relatively large variations in the spatial temperature distribution were found, and they were higher in the vertical direction than in the longitudinal direction. The temperatures measured in the AOZ at 0.25 m height, were on average, 7 °C warmer than that at 1.5 m height. The AOZ temperature correlated better with temperatures measured at 0.7 m or 1.5 m height in the same pen than with temperatures measured in the AOZ at other pens. The analyses show that a proportional–integral based control system effectively counteracts the effects of outdoor wind conditions, and the control system is capable of maintaining the defined optimal temperature at the measurement height. However, the optimum temperatures at the measurement heights above AOZ do not correspond to the measured temperatures in the AOZ. • Temperature gradients exist in both vertical and horizontal direction. • Average temperatures at 0.25 m were 7 °C warmer than at 1.5 m for 50% of time. • Temperature gradients were worst during the winter and periods with no wind. • Maintaining optimal temperature at control sensors alone is not sufficient for pigs. • Temperatures experienced by pigs are not reflected by control temperatures.

Evolution of NH3 Concentrations in Weaner Pig Buildings Based on Setpoint Temperature

Ammonia (NH3) concentration has seldom been used for environmental control of weaner buildings despite its impact on environment, animal welfare, and workers’ health. This paper aims to determine the effects of setpoint temperature (ST) on the daily evolution of NH3 concentration in the animal-occupied zone. An experimental test was conducted on a conventional farm, with ST between 23 °C and 26 °C. NH3 concentrations in the animal-occupied zone were dependent on ST insofar as ST controlled the operation of the ventilation system, which effectively removed NH3 from the building. The highest NH3 concentrations occurred at night and the lowest concentrations occurred during the daytime. Data were fitted to a sinusoidal model using the least squares setting (LSS) and fast Fourier transform (FFT), which provided R2 values between 0.71 and 0.93. FFT provided a better fit than LSS, with root mean square errors (RMSEs) between 0.09 ppm for an ST of 23 °C and 0.55 ppm for an ST of 25 °C. A decrease in ST caused a delay in the wave and a decrease in wave amplitude. The proposed equations can be used for modeling NH3 concentrations and implemented in conventional controllers for real-time environmental control of livestock buildings to improve animal welfare and productivity.

Numerical investigation on effects of side curtain opening behavior on indoor climate of naturally ventilated dairy buildings

The side-curtain is popular in cattle buildings to regulate indoor climates and ventilation rates by adjusting the opening ratio. It normally had three different adjusting strategies relate to the position of rollers, i.e. central roller (S1), top roller (S2) and bottom roller (S3), which result in different opening behaviors to generate the same opening ratio but different opening positions in the side wall for a full-curtain house. Numerical simulations were conducted using computational fluid dynamics (CFD) to investigate the effects of the eight potential opening behaviors of side curtains on the indoor climates and airflow rates in winter for a typical naturally ventilated dairy house in China when the opening ratio were 8.5% and 17%. Airflow patterns, wind chilled temperature (WCT) and age of air were analyzed in the animal occupied zone (AOZ) by taking reference planes. Openings at the very bottom of side walls had more efficient ventilation due to the younger air age, more effective air disturbing, more uniformly distributed indicators in AOZ. However, it will result in a lower WCT in AOZ although a lower ventilation rate was observed in this case. Openings on the very top of side wall would generate a better thermal comfort in AOZ but with very poor air quality and nonuniformly distributed airflows in the dairy house. S1 was not recommended to the practical application due to the poor indoor climate and the higher cost of the mechanical structure. Based on the comprehensive evaluations of the analytic hierarchy process, the most satisfaction opening positions were at the bottom of the side curtains and the optimized adjusting strategy is S2. Keywords: thermal comfort, age of air, ventilation rate, computational fluid dynamics, analytic hierarchy process DOI: 10.25165/j.ijabe.20201305.5805 Citation: Li Q F, Yao C X, Ding L Y, Yu L G, Ma W H, Gao R H, et al. Numerical investigation on effects of side curtain opening behavior on indoor climate of naturally ventilated dairy buildings. Int J Agric & Biol Eng, 2020; 13(5): 63–72.

Computational fluid dynamics evaluation of pig house ventilation systems for improving the internal rearing environment

Due to the cold stress experienced by pigs, and the increased energy load during winters and the changes from winter to spring and summer to autumn, it is difficult to provide sufficient ventilation in pig houses. These factors can result in a poor internal environment. Therefore, fundamental measures to increase the ventilation rate and a corresponding analysis of the effects were needed to improve internal rearing environment. Due to the characteristics of invisible air, it was difficult to analyse the aerodynamic characteristics inside a pig house by field experiment. Computational fluid dynamics (CFD) has been used to overcome such limitations for the last 30 years. In this study, environmental monitoring (air temperature, humidity, etc.) in a commercial pig house were conducted to identify environmental problems. After this, CFD validated models were designed and evaluated to find effective solutions, by changing the conditions of the pig house air inlets and outlets (air buffer space, inlet duct, and exhaust fan). Compared with the conventional ventilation system of the experimental pig house, adjusting the hole spacing of the inlet duct and installing a roof–chimney exhaust fan did not significantly improve the rearing environment. However, when an air buffer space was installed just before the location of the inlet on the sidewall, the air temperature flowing through the air buffer space increased making it possible to supply more than twice the external air to the pig house, while maintaining the air temperature distribution at the height of the animal-occupied zone.

Assessment of optimal airflow baffle locations and angles in mechanically-ventilated dairy houses using computational fluid dynamics

Baffles are often installed in mechanically cross-ventilated barns to combat heat stress by enhancing the cooling effect produced by the barn’s design. How effectively these baffles operate during warm weather often depends on where each baffle is located and at what angle it is set. Currently, their location and orientation are determined primarily according to the personal experience of the contractor in charge of installing the barn’s ventilation system. This study seeks to quantify the extent to which the location and orientation may affect the efficiency of the installed baffles. Computational fluid dynamics was used to create a three-dimensional model of a typical low-profile, cross-ventilated dairy barn. Differences were evaluated using both heat transfer and heat stress index (the Equivalent Temperature Index for Cattle - EITC). The results obtained from the tested scenarios indicated that installing the baffles above the animal occupied zone (AOZ) could indeed increase the air velocity (from less than 0.5 m s−1 to around 3 m s−1 once baffles were in place), and could also greatly increase (by 21.1%–50.9%) the amount of heat removed, while reducing the EITC by ~6 °C. In comparisons between the most commonly used scenario (in which baffles were installed vertically in the middle of the AOZ), and the other with-baffle-scenarios, the rate at which heat was removed from the cows varied by −3.0% to 2.6%, with the maximum difference being 172.4W. However, these scenario produced no significant improvement comparing with the commonly used one. The results obtained should provide a more reliable reference for engineers engaged in designing large-scale dairy barns.

Numerical simulation of airflow in animal occupied zones in a dairy cattle building

Air flow assessment in animal husbandry is an important issue in the context of welfare and emission. The aim of this study was to implement a porous medium approach for the numerical simulation of air flow in the animal occupied zone (AOZ) of a dairy building. Computational fluid dynamics (CFD) was used to determine the flow resistance properties, where cow geometry was simplified by a six-cylinder geometry. Three different AOZ were identified and parametric studies were performed to determine the pressure drop depending on the air inlet angle. Viscous and inertial loss terms were calculated by non-linear regression and added to the Navier-Stokes equations for each AOZ as a subdomain. Simulations of the air flow in a barn segment containing the three AOZ (standing, resting and resting in double line) indicated that in most configurations, inertial forces dominated and pressure drop was dependent on the air inlet angle. The viscous and inertial loss terms changed depending on the AOZ. The total pressure drop predicted using the porous medium approach taking into account the different AOZs was in good agreement with the results obtained by simulations using the fully resolved, simplified cow bodies.

CFD prediction of convective heat transfer and pressure drop of pigs in group using virtual wind tunnels: Influence of grid resolution and turbulence modelling

Ventilation for the animal house is important since it is highly linked with the convective heat removal from animals. In this context, the animals as obstacles affect the ventilation airflow and consequently the air distribution within Animal Occupied Zone (AOZ). To study the convective heat transfer (CHT) of animals and the pressure drop (PD) resulting from the animals, computational fluid dynamics (CFD) can be an efficient tool, particularly in comparison with experimental methods. However, simulation accuracy is influenced by grid treatment and the choice of turbulence models. To reveal the grid effects on CHT and PD, fifteen 3D meshes with different facial grids sizes (0.04 m, 0.02 m, and 0.008 m) and prismatic layer thicknesses (PLT) (0 m, 0.0015 m, 0.009 m, 0.02 m, 0.04 m) were tested based on staggered tube bundle models representing simplified bluff bodies using virtual wind tunnels. Then, four commonly used turbulence models, namely, standard k–ɛ, realisable k–ɛ, standard k–ω, and SST k–ω, together with two wall treatments were evaluated and compared with the empirical calculation. The evaluation of turbulence models and wall treatment was then carried out based on grouped pig models using virtual wind tunnels. The results showed that the PLT could be an important influence on the stability of the simulation with varied facial grid sizes. The k–ω models performed better than the k–ɛ models on the predictions of both the CHT and the PD based on the tube bundle model. Wall function provided acceptable results on CHT, however, significant flaws on the PD on both tube bundles and pig models.

Wind tunnel investigations of sidewall opening effects on indoor airflows of a cross-ventilated dairy building

Well-understanding indoor air movement with respect to openings in naturally-ventilated buildings is essential to provide healthy and comfortable indoor climate for livestock. This study investigated the effects of the sidewall opening configurations on internal airflow fields and air velocity characteristics within the animal occupied zone (AOZ). Eight cases with varied opening ratios and locations were tested under 8 m•s-1 free wind speed and wind direction perpendicular to the sidewalls. The ‘up-jet’ airflow pattern was observed when the opening ratio was no greater than 62.71% and the openings located beneath the eaves. Air went across the AOZ without circulating with the surrounding air when no sidewalls were installed below the AOZ height. Both air speed and turbulent kinetic energy increased when the opening was bigger with Pearson's correlation coefficients of 0.8 and 0.9 respectively, but the relationship between the opening size and the turbulence intensity was more complex. Uniform air speed distributions were observed in the AOZ with high sidewalls on bottom. By contrast, the air speed heterogeneity in the AOZ was found when sidewall heights were below the AOZ height. We conclude that care should be taken when using these kinds of opening configurations during extreme cold windy weather conditions.

Effect of airflow speed and direction on convective heat transfer of standing and reclining cows

An effective ventilation system can mitigate the heat stress suffered by dairy cows by increasing the rate at which heat is transferred convectively from a cow into the air flowing around the animal. To achieve a better understanding of the main factors involved in the heat-transfer process (i.e., the cow's posture and the airflow magnitude and direction), numerical investigations were conducted during the course of this study. By applying a computational fluid dynamics (CFD) modelling method, a virtual wind tunnel, and simplified geometric models representing a standing cow and a reclining cow, the heat transfer associated with a typical cow was simulated and analysed. The shear stress transport (SST) k–ω turbulence model was adopted, and it was shown that using a CFD method to analyse the heat-transfer data generated by this setup could produce results that are accurate and support the following conclusions: 1) airflow speed has a positive effect on the convective heat-transfer coefficient associated with both postures; 2) airflow direction affects the convective heat transfer coefficient, with the largest coefficient occurring in the cross flow case and the lowest in the downward airflow case; 3) the effect of posture on the convective heat transfer coefficient in a horizontal airflow is limited, whereas the effect in a downward airflow is relatively significant. However, the rate at which heat dissipates from a standing cow is greater than that of reclining cow, since a standing cow has more surface area in contact with the air. Based on these conclusions, it is recommend that, to cool cows under hot conditions, the airflow in the animal-occupied zone should be increased and that using a horizontal airflow to target the animal occupied zone should be encouraged whenever it is feasible to create.

A Computational Fluid Dynamics Model of Biological Heat and Gas Generation in a Dairy Holding Area

Abstract.The design and operation of ventilation systems for animal housing is a crucial component in maintaining a suitable environment for both animals and workers by removing heat, moisture, and gas species. However, important design and operational criteria, such as profiles of velocity and extent of mixing within animal housing, can be difficult to study experimentally. Thus, a computational fluid dynamics (CFD) model of a commercial dairy holding area, including the generation of transport of heat and gas species within the domain, was developed. The animal-occupied zone (AOZ) was modeled using porous media. The model was evaluated with experimental data of velocity and gas concentration. Results indicated that the airflow uniformity and air speed could be increased within the holding area by modifying the configuration of the side curtain openings and using concrete walls to guide airflow; a 20% increase in average velocity within the AOZ was achieved. Results of the CFD model have shown it to be an effective tool for gaining insight into the complex mixing patterns within holding areas to improve the design of animal housing. Keywords: Animal-occupied zone, Computational fluid dynamics, Greenhouse gas emissions, Holding area.

Numerical study on the convective heat transfer of fattening pig in groups in a mechanical ventilated pig house

It is recognized that increasing the local air speed in the animal occupied zone (AOZ) is one of the effective approaches to decrease the heat stress of pigs. To predict the effects of the air speed in an AOZ, knowledge of the relationship between convective heat loss and air speed is essential. In this study, the convective heat losses from pig models were modelled through numerical simulation under semi-practical conditions. The convective heat transfer coefficients of pigs in groups were tested at different inlet speeds. Virtual pig bodies (pig models) corresponding to three different body weights, i.e., 30kg, 50kg, and 80kg, were generated and used in the investigation. Two wall inlet styles, a conventional inlet with an upward guiding plate and a modified inlet that supplied downward airflow directly onto the pigs, were compared to estimate the effect of ventilation system on the convective heat loss of pigs. The results showed that convective heat transfer coefficients of pigs in a group were strongly correlated with the inlet air speeds as well as the reference air speed in the AOZ (the average air speed in AOZ was selected as reference air speed in this study). The weight of the pig models showed no significant effect on the convective heat transfer coefficient. The convective heat transfer coefficient of the pigs in pens with the downward inlet was averagely 60.4% higher than those with the upward inlet.

Assessing response surface methodology for modelling air distribution in an experimental pig room to improve air inlet design based on computational fluid dynamics

The thermal comfort of pigs is strongly correlated with the air motion around the pigs. In a pig production building, it is the ventilation system that influences the indoor air distribution significantly. In the ventilation system design, air inlet is considered to be important on the air motion in room. In this study, the Response Surface Methodology (RSM) was evaluated to develop the prediction model of the air speed in animal occupied zone (AOZ). Three dimensional numerical simulations for an experimental pig room were conducted to estimate the air speeds within the AOZ with the inlet supplying air in different angles and airflow rates on three installation heights of inlets. The results showed the RSM was capable to model the air speed in AOZ. Based on sensitivity analysis, the initial air speed and angle significantly influenced the air speed at the AOZ level, while the installation height was a less significant parameter. The RSM models could be used for design and control of an optimal ventilation system to achieve a better environment for pigs.

Reliability of turbulence models and mesh types for CFD simulations of a mechanically ventilated pig house containing animals

The use of computational fluid dynamics (CFD) to study the airflow within farm animal buildings is increasing. The choice of turbulence model within CFD is generally considered to be important due to the approximations of the turbulence in varied scales. Although some studies have been conducted on evaluations of turbulence models in simulation of airflow in ventilated rooms, knowledge of airflow in the animal occupied zone (AOZ) with airflow blockage by the animals and knowledge of thermal convection effects are still limited. In this study, five commonly used two-equation turbulence models (standard k – ɛ , realisable k – ɛ , RNG k – ɛ , standard k – ω , and SST k – ω ) were applied to a CFD model of the airflow in a mechanically ventilated pig room with animals housed in pens. In addition to turbulence models, the effects of non-conformal meshing which combines several computational sub-domains and connects the boundary of domains using interfaces, were tested. The effect of mesh ratio on the interface (i.e. ratio of the grid number of the up and down interface) was studied based on fully structural hexahedral mesh (SH). The investigation of mesh type effect was conducted by application of an unstructured tetrahedral mesh (UT) in the AOZ and SH in the rest of the domain. The results showed that the choice of turbulence model did not have a strong effect on the main airflow pattern except for the RNG k – ɛ model. The tested ratios of resolution at interfaces were also found not to strongly impact on the predicted airflow distributions. The use of UT in the AOZ sub domain also provided acceptable results. It was concluded that non-conformal meshes are a feasible alternative for animal buildings with complex geometries to maintain affordable grid numbers and also reduce the difficulties in mesh generation.

An Evaluation of Simplifying Assumptions in Dairy Cow Computational Fluid Dynamics Models

<abstract> <b><sc>Abstract.</sc></b> Concurrent with the development of technologies and strategies for abating the heat buildup inside dairy barns, there is greater demand for an efficient and accurate way to test their performance. Computational modeling has improved to the point that it is now feasible to create realistic representations of animals to facilitate fluid dynamic modeling. Therefore, this study sought to use computational fluid dynamics to create and evaluate six different cow geometries: a sphere, a cylinder, a rectangular prism, a six-cylinder configuration, and two polygonal geometries labeled “low-polygon cow” and “high-polygon cow.” These six geometries were compared on the basis of their relative ability to replicate the effects of various different cooling and ventilation systems in operation inside a dairy barn. The low-polygon cow, having achieved results similar to the high-polygon cow with a coarser mesh, was then used to test the now common assumption that the area occupied by an animal (commonly called the animal-occupied zone) can be treated as porous media. While all three realistic geometries predicted heat transfer with nearly the same degree of accuracy (all were within 10% of each other), the test showed that key localized differences must be taken into account when selecting a particular geometry. The testing also found evidence in support of the assumption that an animal-occupied zone should be treated as porous media when evaluating the effects that the zone will have on the rest of the computational domain; however, the animal-occupied zone assumption should not guide any evaluation of the transport phenomena occurring within the zone itself.