On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. There is increasing concern about potential differences between steady flow conditions that are typically used for development and the transient conditions that occur on-road. This work considers whether steady techniques are able to predict the unsteady results measured on-road, the impact of this unsteadiness on the noise perceived in the cabin and whether minor changes made to the geometry of the vehicle could affect this. Both external aerodynamic and acoustic measurements were taken using a full-size vehicle combined with measurements of the noise inside the cabin. Data collection took place on-road under a range of wind conditions to accurately measure the response of the vehicle to oncoming flow unsteadiness, with steady-state measurements taking place in full-scale aeroacoustic wind tunnels. Overall it was demonstrated that, using a variety of temporal and spectral approaches, steady techniques were able to predict unsteady on-road results well enough to assess cabin noise by correctly taking into account the varying on-road flow conditions. Aerodynamic admittance values remained less than unity in the sideglass region of the vehicle, with the exception of the the region nearest the A-pillar. The reducing unsteady energy at frequencies greater than 10 Hz, combined with the corresponding roll-off in admittance, implies that unsteady frequencies below 10 Hz affect the vehicle most, where the response remains quasi-steady. Quasi-steady cabin noise simulations allowed a subjective assessment of the predicted unsteady cabin noise, where the impact of cabin noise modulations were quantified and found to be important to perception. Minor geometry changes affected the sensitivity of cabin noise to changes in yaw angle, altering modulation and therefore having an important impact on the unsteady wind noise perceived on-road.

No description available.

Most heavy goods vehicles in service today are fitted with add-on aerodynamic devices. The most common of which is the cab-mounted roof deflector. Such devices provide appreciable drag savings, however, they are often not optimised for the trailer. When a wind yaw angle is present, their savings also diminish as the yaw angle increases. The work conducted within this thesis investigated the possibility of using an adjustable deflector for active flow control. The optimum deflector height for a given trailer height was initially investigated using wind tunnel testing. The variation of this optimum with yaw angle and container separation was then investigated. From the results a 3D look-up table was generated. A control scheme was proposed that used the 3D look-up table requiring only three measurable inputs. The three inputs required were: the wind yaw angle, the container height and the container separation. A pressure differential located on the deflector was found to linearly relate to the wind yaw angle. This relationship allowed on-road measurement of the wind yaw angle and therefore enabled the development of a prototype controller. Extensive on-road testing and unsteady computational simulation were conducted. The results obtained indicated a mean yaw angle magnitude of around 5 perturbed by four fundamental low frequencies. These frequencies were identified in the runs conducted over the test period and an average frequency established. Higher frequency disturbances were attributed to the wakes of leading heavy goods vehicles and were filtered by a suitably chosen numerical filter. Finally, an estimation of the efficiency of the active device was made using a combination of simulation and full scale testing. From the results obtained, an optimised deflector generated an average drag reduction of 7.4%. An estimated additional drag reduction of 1.9% over the optimised deflector was predicted through use of an active system.

Local air quality is one of the factors constraining the development of airports. In countries of the European Union where new, stricter regulations for emissions of nitrogen oxides (NOx) have been introduced since 2010, the limits of mean annual concentrations are already exceeded at certain ground monitoring locations of large airports. This research project investigates the possibility of abating the aircraft exhaust plume at take-off by placing an array of aerodynamic windbreaks (‘baffles’) in the runway end safety area close to the aircraft starting position. The undertaken experimental investigation comprised sub-scale wind tunnel tests and full-scale field trials with a BAe 146-301 aircraft, performing take-off and landing cycles at Cranfield Airport. The initial wind tunnel experiments investigated the effect of a solid baffle row, placed in the path of a buoyant nozzle jet, on the development of the plume downstream. Using flow visualisation, the positive effect of the baffle row of promoting buoyant rise of the plume away from the ground was demonstrated successfully without the presence of wind tunnel flow. The investigation highlighted the importance of the distance of the baffles relative to the jet source on their effectiveness. In the presence of wind tunnel flow, the baffles caused an increased vertical spread of the plume downstream, but the plume was not observed to separate from the ground. In preparation of the field trials, the spatial arrangement of the baffle array was investigated by means of wind tunnel drag measurements, performed with a skinfriction balance. The experiments focused on key parameters such as the baffle slope angle and row spacing, favouring a configuration of three rows of baffles of increasing height. Based on the wind tunnel measurements, full-scale baffle prototypes were designed and manufactured at Cranfield University and were deployed in the field trials. Lidar and point sampler measurements during the field trials suggested that the plume had risen away from the ground on one occasion when the aircraft was located close to the baffles. A positive effect was shown in terms of reduced concentrations downstream of the baffles. This result was not replicated when the aircraft was further away from the baffles. The subsequent wind tunnel experiments focused on replicating the field trials at 1:200 scale in Cranfield’s Atmospheric Boundary Layer Wind Tunnel. The aircraft was represented at sub scale with a single stationary nozzle while the jet speed and buoyancy were modelled using similarity parameters such as the Froude number and the ratio of ambient and jet density. Mean concentration measurements were performed using a Flame Ionisation Detector method releasing methane as tracer gas. The effect of the baffles was observed to be mainly local in terms of reduced concentrations close the ground due to their sheltering effect. A more prolonged effect was found to be the increase of the plume’s vertical spread resulting in an increase in mean concentrations away from the ground.

Operation of Unmanned Aerial Vehicles (UAVs) in civil airspace is restricted by the aviation authorities which require full compliance with regulations that apply for manned aircraft. This thesis proposes control algorithms for a collision avoidance system that can be used as an advisory system or a guidance system for UAVs that are flying in civil airspace under visual flight rules. An effective collision avoidance system for the UAV should be able to perform the different functionalities of the pilot in manned aircraft. Thus, it should be able to determine, generate, and perform safe avoidance manoeuvres. However, the capability to generate resolution advisories is crucial for the advisory systems. A decision making system for collision avoidance is developed based on the rules of the air. The proposed architecture of the decision making system is engineered to be implementable in both manned aircraft and UAVs to perform different tasks ranging from collision detection to a safe avoidance manoeuvre initiation. Avoidance manoeuvres that are compliant with the rules of the air are proposed based on pilot suggestions for a subset of possible collision scenarios. The avoidance manoeuvre generation algorithm is augmented with pilot experience by using fuzzy logic technique to model pilot actions in generating the avoidance manoeuvres. Hence, the generated avoidance manoeuvres mimic the avoidance manoeuvres of manned aircraft. The proposed avoidance manoeuvres are parameterized using a geometric approach. An optimal collision avoidance algorithm is developed for real-time local trajectory planning. Essentially, a finite-horizon optimal control problem is periodically solved in real-time hence updating the aircraft trajectory to avoid obstacles and track a predefined trajectory. The optimal control problem is formulated in output space, and parameterised by using B-splines. Then the optimal designed outputs are mapped into control inputs of the system by using the inverse dynamics of a fixed wing aircraft.

Weather radar has been widely used in hydrologic forecasting and decision making; nevertheless, there is increasing attention on its unceltainties that propagates through hydrologic models. These unceltainties are not only caused by radar itself in measuring and estimating rainfall (such as attenuation, extrapolation of the rainfall measured aloft to the ground, sampling methods and pmtial beam blocking, etc.), but also come from the complicated synoptic regimes (such as air motion, vertical variability of temperature, and conversion to and from different hydrometeors). This thesis aims to improve the quality of radar rainfall and describe its uncertainty. The Brue catchment (135 sq. km) in Southwest England covering 28 radar pixels and 49 rain gauges and a hilly area to the east and south of Manchester with around 5000 sq . km and 50 rain gauges are chosen as the experimental domains for this thesis. The studies are composed of three main pmts: Firstly, I propose a fully formulated uncertainty model that can statistically quantify the characteristics of the radar rainfall errors and their spatial and temporal structure, which is a novel method of its kind in the radar data unceltainty field. The uncertainty model is established based on the distribution of gauge rainfall conditioned on radar rainfall (GRJRR). Its spatial and temporal dependences are simulated based on the copula function. With this proposed uncertainty model, a Multivariate Distributed Ensemble Generator (MDEG) driven by the copula and autoregressive filter is designed. The products from MDEG include a time series of ensemble rainfall fields with each of them representing a probable true rainfall. As wind is a typical weather factor that influences radar measurement, this thesis introduces the wind field into the unceltainty model and designs the radar rainfall uncertainty model under different wind conditions. In addition, I also propose an Empirically-based Ensemble Rainfall Forecasts (ERFEM) model to measure and quantify the combined effect of all the error sources in the radarrainfall forecasts .. The essence of the unceltainty model is formulated into an empirical relation between the radar rainfall forecasts and the corresponding 'ground truth' represented by the rainfall field from rain gauges. In modelling the radar rainfall unceltainty, I find that the wind has a huge impact on radar-gauge comparison. Due to the wind effects, the raindrops observed by the radar do not always fall veltically to the ground, and the raindrops arriving at the ground cannot all be caught by the rain gauge. This thesis proposes a practical approach to simulate the movement of raindrops in the air and adjust the aforementioned wind-induced errors on radar bias correction procedure. This scheme is based on the numerical simulation of raindrop movements in the three-dimensional ' wind field. The Weather Research and Forecasting (WRF) model is used to downs.cale the reanalysis data ERA-40 to obtain the wind field with high spatial and temporal resolutions. A normalized gamma model is adopted to estimate the raindrop size distribution (DSD). This work is the first study to tackle both wind effects on radar and rain gauges, which could be considered as one of the essential components in processing radar observation data, which should be undertaken after the aforementioned physical processes and before bias correction. Finally, this thesis analyzes how the radar rainfall uncertainty propagates through a hydrological model (the Xinanjiang model) and investigates which features of the uncertainty model have significant impacts on flow simulation. The generated ensemble rainfall values by MDEG are input into the Xinanjiang model to produce uncertainty bands of the ensemble flows. Five important indicators are used to describe the characteristics of uncertainty bands. It is concluded that the Gaussian marginal distribution and spatio-temporal dependence using Gaussian copula is considered to be the preferred configuration of the MDEG model for hydrological model unceltainty analysis in the Brue catchment. Keywords: Multivariate Distributed Ensemble Generator (MDEG); Copula; flow simulation; Radar-Rainfall Estimates; Hydrological Model Uncertainty; wind-induced error; drop size distribution; WRF; wind-drift.

The full autonomous control of a rotary-wing Micro Aerial Vehicle (MAV) relies on measurement inputs from sensors to allow the vehicle to maintain a constant position in a 3D environment. Monocular Visual SLAM (VSLAM) is a particularly efficient sensing method in terms of payload cost. A single camera can be used to provide a full 6-DOF pose measurement, however, this is at the cost of increased communication bandwidth and computational requirements, often resulting in low-rate and delayed feedback measurements. This thesis presents an investigation into the use of VSLAM feedback to stabilise the full 3D position of a MAV. To reach this goal, experimental work is conducted using small rotary-wing platforms in indoor environments. Platforms include the static 3-DOF Quanser and the 6-DOF AR.Drone2.0 quadrotor. Theoretical dynamic models are developed and simplified into decoupled linear sub-systems. The sensing properties of VSLAM are also experimentally identified for both static and dynamic flight scenarios. The control challenge of low-rate delayed measurements is overcome by applying discrete-time LQG control design methods. A discretisation method is detailed which can represent arbitrary delays in a discrete state-space form whilst preserving the dynamic behaviour. A method of tuning the LQG to preserve the reference tracking response is presented, making use of the discrete delayed model structure. Initially the presented control design is experimentally applied to SISO systems to assess the performance, making use of high accuracy external tracking systems. The result is then extended to the full 6-DOF helicopter where free flight is demonstrated, using VSLAM as the only pose measurement, with no additional sensors required to initialise VSLAM.

No description available.

A tool based on a Techno-economic and Environmental Risk Assessment (TERA) framework is useful at the preliminary stage of an aero engine design process, to conceive and assess engines with minimum environmental impact and lowest cost of ownership, in a variety of emission legislation and taxation policy scenarios. This research was performed as part of the EU FP6 New Aero engine Core concepts (NEWAC) programme which was established to assess the potential of innovative gas turbine core technologies to enhance thermal efficiency thereby reducing CO2 emissions and fuel consumption. A representative prediction of engine life and mission fuel burn at the earliest possible design stage is a crucial task that can provide an indication of the approximate overall engine direct operating costs. Two aero engines, a conventional turbofan and a conceptual intercooled turbofan, were assessed and optimised using the TERA approach to identify the designs that provided the maximum time between overhaul (and therefore the minimum maintenance costs). In order to perform these assessments (which included sensitivity and parametric analyses, and optimisation studies) several models were developed and integrated in an optimisation framework. A substantial effort was devoted to the development of a detailed lifing model that calculates the engine life with a reasonable level of accuracy by integrating physics based oxidation, creep and fatigue models. The results obtained from the study demonstrate that an engine optimised for maximum time between overhaul requires a lower overall pressure ratio and specific thrust but this comes at the cost of lower thermal efficiency and therefore higher mission fuel burn. The main contribution to knowledge of this work is a multidisciplinary TERA assessment of a novel intercooled conceptual aero engine. Particular emphasis is placed on the design space exploration and optimisation studies to identify the designs that may offer the largest time between overhaul. The consequent implications therefore this may have on mission fuel burn and direct operating costs. In addition to refining the various TERA models, one of the main recommendations for further work is to optimise the engines for minimum direct operating cost to identify the best economic compromise between engine life and mission fuel burn. This can be done by considering different fuel prices and under a variety of hypothetical emission taxation scenarios, to identify the circumstances in which intercooled engine technology may become economically viable.

The life and performance of axial compressors are limited by the occurrence of instabilities such as rotating stall and surge. Indeed, in the course of the design phase a great effort is usually devoted to guarantee an adequate safety margin from the region of instabilities’ onset. On the other hand, during its operating life, an axial compressor can be subjected to several conditions that can lead to the inception of stall and its dynamics. A few examples of possible stall causes, for the specific case of an axial compressor embedded in an aircraft engine, are inlet flow distortion, engine wear or shaft failure. The shaft failure case can be seen as an exception, as a matter of fact, after this event surge is a desirable outcome since it can potentially decelerate the over-speeding turbine by reducing the mass flow passing through the engine. The possible occurrence of surge and stall should be predicted and controlled in order to avoid severe damage to the compressor and its surroundings. A lot of research has been carried out in the past years to understand the inception and development of stall to achieve the capability for predicting and controlling this severe phenomenon. Nonetheless, this problem is still not well understood and unpredictable outcomes are still a great concern for many axial compressor’s applications. The lack of knowledge in what concerns inception and development of stall and surge reflects in a lack of tools to investigate, predict and control these unstable phenomena. The tools available to study stall and surge events are still not highly reliable or they are very time consuming as 3D CFD simulations. The doctoral research described herein, aimed at the investigation of the rotating stall phenomenon and the derivation of the compressor characteristic during this unstable condition. Following a detailed analysis of the tools and techniques available in the public domain and the identification of their limitations, the development of a FORTRAN through-flow tool was the methodology chosen. A distinctive feature of the developed tool is the independency from steady state characteristics which is a limitation for the majority of the available tools and its computational efficiency. Particular attention was paid to capture various viscous flow features occuring during rotating stall through the selection and implementation of appropriate semiempirical models and correlations. Different models for pressure loss, stall inceptions and stall cell growth/ speed were implemented and verified along with different triggering techniques to achieve a very close to reality simulation of the overall phenomenon, from stall inception to full development. lel compressors’ technique that allows the correct modeling of asymmetric phenomena. The methodology implemented has proved promising since several simulations were run to test the tool adopting different compressor geometries. Verifications were performed in terms of overall compressor performance, with simulations in all the three possible operating regions (forward, stall and reverse flow), in order to verify the tool’s capability in predicting the compressor characteristics. In terms of flow field, the ability to capture the right circumferential trends of the flow properties was checked through a comparison against 3D CFD simulations. The results obtained have demonstrated the ability of the tool to capture the real behavior of the flow across a compressor subjected to several different unstable conditions that can lead to the onset of phenomena such as rotating stall, classic and deep surge. Indeed, the tool has shown ability to tackle steady and transient phenomena characterized by asymmetric and axis-symmetric flow fields. This document provides several examples of investigations emphasizing the flexibility of the developed methodology. As a matter of fact, within this dissertation, many examples can be found on the effect of the plenum size, on the different transient phenomena experienced by the compressor when subjected to multiple regions of inlet distortion instead of a localized region of low or high flow, on the differences between temporary and stationary inlet disturbances and so on. This document describes in detail the methodology, the implementation of the tool, its verification and possible applications and the recommended future work. The work was funded by Rolls-Royce plc and was carried out within the Rolls-Royce UTC in Performance Engineering at Cranfield as three-year Ph.D. program that started in October 2010.