Aerodynamic shape optimization of a low drag fairing for small livestock trailers

Small livestock trailers are commonly used to transport animals from farms to market within the United Kingdom. Due to the bluff nature of these vehicles there is great potential for reducing drag with a simple add-on fairing. This paper explores the feasibility of combining high-fidelity aerodynamic analysis, accurate metamodeling, and efficient optimization techniques to find an optimum fairing geometry which reduces drag, without significantly impairing internal ventilation. Airflow simulations were carried out using Computational Fluid Dynamics (CFD) to assess the performance of each fairing based on three design variables. A Moving Least Squares (MLS) metamodel was built on a fifty-point Optimal Latin Hypercube (OLH) Design of Experiments (DoE), where each point represented a different geometry configuration. Traditional optimization techniques were employed on the metamodel until an optimum geometrical configuration was found. This optimum design was tested using CFD and it matched closely to the metamodel prediction. Further, the drag reduction was measured at 14.4% on the trailer and 6.6% for the combined truck and trailer

Ventilation of small livestock trailers

A large number of livestock is transported to market in small box trailers. The welfare of animals transported in this way is now assuming greater importance with the onset of tougher EU legislation. This paper presents the first study into the ventilation of small livestock trailers using experimental and computational methods. Wind tunnel studies, using a 1/7th scale model, highlight the important influence of the towing vehicle and trailer design on the airflow within the trailer. Detailed CFD analysis agrees well with the wind tunnel data and offers the ability to assess the impact of design changes

Modeling infection risk and energy use of upper-room Ultraviolet Germicidal Irradiation systems in multi-room environments

The effectiveness of ultraviolet irradiation at inactivating airborne pathogens is well proven, and the technology is also commonly promoted as an energy-efficient way of reducing infection risk in comparison to increasing ventilation. However, determining how and where to apply upper-room Ultraviolet Germicidal Irradiation devices for the greatest benefit is still poorly understood. This article links multi-zone infection risk models with energy calculations to assess the potential impact of a Ultraviolet Germicidal Irradiation installation across a series of inter-connected spaces, such as a hospital ward. A first-order decay model of ultraviolet inactivation is coupled with a room air model to simulate patient room and whole-ward level disinfection under different mixing and ultraviolet field conditions. Steady-state computation of quanta-concentrations is applied to the Wells–Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative influence of different design factors for susceptible patients co-located with an infectious source or in nearby rooms. In each case, energy requirements are calculated and compared to achieving the same level of infection risk through improved ventilation. Ultraviolet devices are seen to be most effective where they are located close to the infectious source; however, when the location of the infectious source is not known, locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones. Results show an ultraviolet system may be an energy-efficient solution to controlling airborne infection, particularly in semi-open hospital environments, and considering the whole ward rather than just a single room at the design stage is likely to lead to a more robust solution

An experimental and computational study of the aerodynamic and passive ventilation characteristics of small livestock trailers

This paper presents a combined experimental and computational study of the aerodynamics and passive ventilation characteristics of small livestock trailers within which the majority of animals in the United Kingdom are transported to market. Data obtained from a series of wind tunnel experiments using a 1/7th scale model of a simplified towing vehicle and trailer is compared with complementary Computational Fluid Dynamics (CFD) analyses, based on steady-state RANS turbulence modelling, of the coupled external/internal flow field. Good agreement between the two is obtained everywhere except at the rear of the trailer. Since the internal flow field and overall ventilation rates contribute to animal welfare, CFD is used to generate detailed internal flow fields and air residence times for use within an overall welfare assessment. The results demonstrate that the flow fields in the upper and lower decks differ significantly and that ventilation rates are much larger and air residence times much smaller on the upper deck

Quantifying Passive Ventilation within Small Livestock Trailers using Computational Fluid Dynamics

This paper illustrates three different methods which can be used to quantify passive ventilation inside small livestock trailers. Accomplishing this is crucial to determine whether animal welfare ventilation standards are met during road transport. High-fidelity Computational Fluid Dynamics (CFD) simulations are conducted for a detailed livestock trailer containing 48 sheep and coupled to a generic towing vehicle. An initial correlation study shows that the observed airflow patterns share the general flow structure with an equivalent but simplified geometry which has previously been validated. Further analysis of the detailed geometry shows that twice as much air flows through the upper deck of the trailer compared to the lower deck which is due to a tailboard vent allowing easier passage to the low-pressure wake. Ventilation is analysed using the net flow rate through vent openings along the side of the trailer; it is found to be below the regulatory threshold for vehicle speeds of up to 17.9 m/s on the lower deck and 8.9 m/s on the upper one. One drawback of this analysis method is that it does not consider ventilation efficacy within the interior. In order to address this, two additional methods are proposed to identify ventilation rates using (i) passive scalars and (ii) a particle tracking algorithm. The former method suggests that the greatest residence time is 30.0 s with the latter indicating a value of 19.5 s; both of these occur in the vicinity of one animal muzzle, in a stagnant airflow region of the lower deck. All three analysis methods are compared to EU-specified regulatory ventilation rates in the form of a ventilation coefficient. Overall, ventilation is shown to be significantly better on the upper deck of the trailer, satisfying current livestock transport regulations at moderate to high vehicle speeds, whereas ventilation is markedly less on the lower deck and potentially below the regulatory threshold

Dealing with numerical noise in CFD-based design optimization

Numerical noise is an inevitable by-product of Computational Fluid Dynamics (CFD) simulations which can lead to challenges in finding optimum designs. This article draws attention to the issue, illustrating the difficulties it can cause for road vehicle aerodynamics simulations. Firstly a benchmark problem is used to assess a range of turbulence models and grid types. Large noise amplitudes up to 22% are evident for solutions computed on unstructured tetrahedral grids whereas computations on hexahedral and polyhedral grid structures exhibit substantially less noise. The Spalart Allmaras turbulence model is shown to be far less susceptible to noise levels than two other commonly-used models for this application. Secondly, multi-objective aerodynamic shape optimization is applied to a fairing for a practical road vehicle which is parameterised in terms of three design variables. Moving Least Squares (MLS) metamodels are constructed from 50 high-fidelity CFD solutions for two objective functions. Subsequent optimization is successful for the first objective, however numerical noise levels in excess of 7% give rise to difficulties for the second one. A revision to the problem leads to success and the construction of a small Pareto Front. Further analysis underlines the inherent capability of MLS metamodels in dealing with noisy CFD responses

A review of Hyperloop aerodynamics

Evacuated tube transport, also known as Hyperloop, is a proposed mode of ground transport that uses depressurised tubes to transport passengers and cargo at high-speeds. The aerodynamic flow regime of a Hyperloop system combines the characteristics of low Reynolds number, high Mach number, and confined/choked flow. This makes it unique compared to more commonly studied aerodynamic problems, and as such it is not yet well understood. This review aims to evaluate the current state of Hyperloop aerodynamics research. First, the effects of low Reynolds number and compressibility in confined flows are explored. Next, 1D analysis is used to determine the theoretical flow characteristics of the Hyperloop. Analytical expressions are derived for the isentropic and Kantrowitz limits, which divide the state-space of the flow into choked and unchoked regimes. The use of Computational Fluid Dynamics to model the flow in the system is then discussed. This is by far the most active area of Hyperloop research, and results from the literature are evaluated and combined here to give further predictions for the expected flow states, which depend on the blockage ratio and Mach number. Finally, aerodynamic design considerations are explored, including the pod and tube geometry, boundary layer transition, ground proximity, ambient temperature, tube breaches and mitigating flow choking using bleed systems