Kevin Knowles

• BSc, PhD
• retired at Cranfield University

Road transportation is a major source of air pollutants that contributes significantly to the exposure of people to poor air quality conditions that are harmful to human health. The present study aims to provide an in-depth insight into the turbulent phenomena of the near-wake of a 50% scaled square-back Ahmed body. Better understanding of these ae...

Air pollution is one of the most important risks to the environment and public health. Exposure to air pollutants can lead to health issues such as lung and heart diseases and even premature death. Human activities such as road transportation contribute significantly to the emission of pollutants into the atmosphere, particularly in urban areas whe...

Pollutant emissions generated by anthropogenic activities such as ground transportation worsen the air quality, particularly in densely populated regions such as urban areas. Due to inhalation of pollutants, people are exposed to health issues such as lung and heart diseases and even premature death. Joint efforts of the health authorities and the...

An experimental study on the processing techniques, bias correction and data convergence using LASER Doppler velocimetry (LDV) is carried out. 2D measurements were obtained in the wake of a 19% scaled square-back Ahmed body for three different incoming velocities (5, 10 and 25 m/s). The effects of commonly used rejection criteria on the presented L...

A ground-effect diffuser is an upwardly-inclined section of an automobile’s underbody which increases aerodynamic performance by generating downforce. To understand the diffuser flow physics (force behaviour, surface and offsurface flow features), we established the near-wake (within one vehicle width of the base) velocity profiles and flow structu...

The transition-sensitive, three-equation k-kL-ω eddy-viscosity closure model was used for simulations of three-dimensional, single-element and multi-element wing configurations operating in close proximity to the ground. The aim of the study was to understand whether the model correctly simulated the transitional phenomena that occurred in the low-...

In this experimental and computational study a novel application of aerodynamic principles in altering the pressure recovery behavior of an automotive-type ground-effect diffuser was investigated as a means of enhancing downforce. The proposed way of augmenting diffuser downforce production is to induce in its pressure recovery action a second pres...

The ground-effect diffuser has become a major aerodynamic device on open-wheel racing and sports cars. Accordingly, it is widely considered to be indispensable to their aerodynamic performance, largely due to its significant downforce contribution. However, the physics and characteristics that determine how it generates downforce and its applicatio...

A ground-effect diffuser is an upward-sloping section of the underbody of a racing car that enhances aerodynamic performance by increasing the downforce, thus improving tire grip. The downforce generated by a diffuser can be increased by geometric modifications that facilitate passive flow control. Here, we modified a bluff body equipped with a 17...

Path generation for mobile robotic manipulator arms is challenging in dynamic environments because high-speed calculations are required to deal with fast-moving obstacles. A novel path-planning algorithm has been developed which solves in quasi-real time the problem of path generation in confined environments for interconnected multi-body systems,...

The influence of the laminar boundary-layer state on a wing operating in ground effect has been investigated using experiments with a model that provides two-dimensional flow. The effect of a boundary-layer trip placed at varying distances from the leading edge was observed at various incidences in terms of on-surface characteristics, including pre...

The transition from a laminar to turbulent boundary layer on a wing operating at low Reynolds numbers can have a large effect on its aerodynamic performance. For a wing operating in ground effect, where very low pressures and large pressure gradients are common, the effect is even greater. A study was conducted into the effect of forcing boundary-l...

Linear first/second order fin direct current (DC) actuator model approximations for missile applications are currently limited to angular position and angular velocity state variables. Furthermore, existing literature with detailed DC motor models is decoupled from the application of interest: tail controller missile lateral acceleration (LATAX) pe...

This paper presents the development of a fourth-order finite difference computational aeroacoustics solver. The solver works with a structured multi-block grid domain strategy, and it has been parallelized efficiently by using an interface treatment based on the method of characteristics. More importantly, it extends the characteristic boundary con...

We report experimental measurements and preliminary analysis on a series of geometric modifications to a rectangular cavity, aimed at alleviating the severity of the aeroacoustic environment. The cavity had a length-to-depth ratio of 5 and a width-to-depth ratio of 1, and featured a simplified representation of a generic missile on the centre line....

The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV):...

In this paper a novel regenerative dual-braking strategy is proposed for utility and goods delivery unmanned vehicles on public roads, which improves their ability to recover regenerative energy and consequently improves the fuel use of parallel hybrid powertrain configurations for land unmanned vehicles where the priority is not comfort but extens...

A comparative study of different passive control techniques was conducted on a cavity with a length of 320 mm with length-to-depth and length-to-width ratios of five and two, respectively. The tests were conducted at a freestream Mach number of 0.71. Both leading-edge and trailing-edge modifications were included in the studies. Results from surfac...

The influence of Reynolds number on the aerodynamic characteristics of various wing geometries was investigated through wind-tunnel experimentation. The test models represented racing car front wings of varying complexity: from a simple single-element wing to a highly complex 2009-specification formula-one wing. The aim was to investigate the influ...

An experimental study was conducted on the effectiveness of sawtooth spoilers at suppressing acoustic tones within a rectangular cavity with a length-to-depth ratio of five and a width-to-depth ratio of two, operating at a freestream Mach number of 0.71. Whereas previous research has focussed on the ratio of spoiler height to boundary-layer thickne...

Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean...

The influence of the yaw angle on a model representative of a monoposto racing car’s front wing and nose section operating in close proximity to the ground is discussed. The yawed condition is representative of a car operating in a crosswind or with side-slip while cornering. Because of the need for downforce in corners rather than on a straight, i...

An experimental investigation was conducted to characterise the gust environment generated by a cascade of sinusoidally oscillating vanes in the Cranfield University 1.52 m by 1.14 m low-speed, open-jet, closed-circuit wind tunnel operating at 7.5 ms−1 and 14.5 ms−1. Measurements were made at four stream-wise and three vertical positions in the flo...

Starting January 2015 the government of the United Kingdom will allow driverless cars on public roads. From a first glance this can and should be seen as a great step towards the adoption of autonomous vehicles. Yet as any new technology driverless vehicles carry with them many new risks and disadvantages that need to be understood and protected ag...

The shortest routing problem is revisited for the case of a dynamically changing environment in an Unmanned Aerial Vehicle (UAV) exploration mission. The latter is represented by energy graphs motivated by [1] and [2]. It is assumed that information about the map is received while on flight due to environmental events. In addition, UAVs are require...

Racing cars are developed in different conditions to those experienced when on track following another car. An experimental and computational study was conducted in order to understand the influence of a leading car on the performance of the front-wing of a trailing car. Force measurement, surface flow visualization and wake surveys allowed for a b...

A study into the effects of forcing boundary layer transition on the suction surface of a GA(W)-1 section wing was undertaken using roughness-type boundary-layer trips. The wing was tested at a range of ground clearances with trips placed at varying chordwise locations using both numerical and experimental techniques. It was shown that forcing tran...

Upon their arrival, Unmanned Autonomous Systems (UAS) brought with them many benefits for those involved in a military campaign. They can use such systems to reconnoiter dangerous areas, provide 24-hr aerial security surveillance for force protection purposes or even attack enemy targets all the while avoiding friendly human losses in the process....

A study was conducted on a GA(W)-1 wing in order to investigate the effect of testing inverted wings in ground effect at low Reynolds numbers. The wing was tested at a range of ground clearances and Reynolds numbers and results showed that the wing's performance was dependent on both these parameters. Surface flow-visualisation and numerical simula...

Energy management system designs for road vehicle applications have for some time considered the use of road data geospatial attributes such as elevation, speed limits and GPS derived online information, like traffic and position, to forecast the amount of fuel that could be consumed by a given vehicle on a specific route. This approach is especial...

This paper focuses on the design of the power management strategy as the key factor in improving the performance in terms of the efficiency, the range and the fuel consumption for a small-scale series hybrid electric vehicle. A complex hybrid vehicle system is considered, and a practically realisable and traceable neurofuzzy strategy for improving...

Particle image velocimetry data are presented from a scaled jet-lift aircraft ground vortex compressible flow. The scaled ground vortex is generated by a vertical compressible jet in cross-flow impinging on a moving ground plane. Particle image velocimetry is used to generate both transient and time-averaged flow statistics from the ground vortex r...

This article gives a novel trajectory generation algorithm which is suitable for operating in confined and dangerous environments. A technique is developed which can, in real time, calculate the existence of a safe path for navigating a robotic manipulator arm between obstacles without collision and accurately generating an efficient path between t...

The effects of scaling on cavity oscillations and control have been studied by measuring the unsteady pressure on the floor of three cavities of different scales. The cavities have a length-to-depth ratio of 5 and a length-to-width ratio of 2, and the corresponding linear dimensions are in the ratio 0.5 : 1 : 2. The experiments were conducted with...

Velocity measurements were made in the near wake of the front wheel of a Formula One car using a laser Doppler anemometer. Tests were carried out on a 50% scale in a closed-return three-quarter open-jet wind tunnel. Three configurations were investigated to determine the effect of both the car and an external wheel support strut on the wheel wake....

This paper presents an experimental investigation of the spanwise flow development on an impulsively started rotating rectangular wing at 45 deg angle of attack. Reynolds numbers of 500 and 15,000 were studied, which correspond to insect and flapping-wing micro-air-vehicle scales, respectively. Stereoscopic particle image velocimetry flowfield meas...

An experimental study incorporating the use of the Background-Oriented Schlieren (BOS) technique was performed to measure the density field of a rectangular supersonic jet. This technique is easier to set up than conventional schlieren since the optical alignment involving the various mirrors, lenses and knife-edge is replaced by a background patte...

A comparative study of different passive control techniques was conducted on a cavity of length 320 mm and L/D and L/W ratios 5 and 2 respectively. The tests were conducted at a freestream Mach number of 0.71. Both leading edge and trailing edge modifications were included in the studies. Results from the pressure measurements showed that leading e...

The incorporation of hydrogen fuel cells into heavy duty tactical mobility vehicles can bring about great opportunities in reducing the pollutant emissions of this kind of platforms (GVW < 30, 000 kg). Furthermore the transportation of fuel to operational areas has become a key aspect for any deployment therefore optimal use of this resource is of...

This paper presents an experimental investigation of the evolution of the leading-edge vortex and spanwise flow generated by an insect-like flapping-wing at a Reynolds number relevant to flapping-wing micro air vehicles (FMAVs) (Re = ~15,000). Experiments were accomplished with a first-of-its-kind flapping-wing apparatus. Dense pseudo-volumetric pa...

An experimental study was conducted to measure some of the turbulence characteristics of a twin-jet fountain-upwash flow using nonintrusive particle image velocimetry. The results show that the point at which the wall jets meet is an area of large horizontal turbulent stress. The largest values of vertical turbulent stress were found in the fountai...

With each passing day, new and more stringent emissions regulations are being introduced in all transportation sectors. The present day commercial airline sector is no stranger to that as exemplified by ICAO agreements signed in 2010; therefore reducing ground pollutant gas and noise emissions has become more important to a point where it has grown...

The incorporation of hydrogen fuel ceils into medium duty vehicles is a research area yet to be explored to its fullest. Although platforms of this weight class (8853 > x >3859 kg. gross vehicle weight rating) are less in number when compared to automobiles, when powered by IC engines they consume more fuel and emit more NOx/particulate matter in n...

Force and moment data are presented for an Ahmed reference model with backlight angles of 10°, 25° and 40° at various distances from a side wall. Tests were run at a freestream velocity of 25 m/s and a rolling road provided ground simulation. Six-component force data were recorded and compared with previous experimental data. It is found that the p...

Experimental work to study the effect of the scale of a model on the flow type within a cavity was carried out using three cavities of different scales. The cavities have a length-to-depth ratio of 5 and length-to-width ratio of 2 and the corresponding linear dimensions are in the ratio 0.5:1:2. Mean-pressure measurements were conducted on the cavi...

This paper proposes fuel cell based electric propul-sion system for Unmanned Aerial Vehicle. Due to high energy density of the fuel cell, the UAV has potential to increase the endurance capacity compared to the battery or combustion engine driven UAVs. The hybrid power plant which consists of proton exchange membrane fuel cell system and the Li-Ion...

Rectangular nozzles are increasingly used for modern military aircraft propulsion installations, including the roll nozzles on the F-35B vertical/short take-off and landing strike fighter. A peculiar phenomenon known as axis-switching is generally observed in such non-axisymmetric nozzle flows during which the jet spreads faster along the minor axi...

The effects of scaling on cavity oscillations and control have been studied by measuring the unsteady pressure on the floors of three cavities of different scales. The cavities have a length-to-depth ratio of 5 and length-to-width ratio of 2 and the corresponding linear dimensions are in the ratio 0.5:1:2. The experiments were conducted with clean...

Insect-like flapping flight offers a power-efficient and highly manoeuvrable basis for micro air vehicles for indoor applications. Some aspects of the aerodynamics associated with the sweeping phase of insect wing kinematics are examined by making particle image velocimetry measurements on a rotating wing immersed in a tank of seeded water. The wor...

In this paper, flow control effectiveness of a passive device in relation to open cavity flowfield is investigated computationally and compared with experimental work. Specifically the modification in the cavity flowfield due to the presence of a spoiler is studied in details to explain the physics behind the flow control effects. A combination of...

In this paper, the results of computational studies on the unsteady flow features in three-dimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer a...

The method of characteristics is used to implement the various boundary conditions (e.g. wall and interface) in a high-order computational aeroacoustic (CAA) code developed by the first author. Most characteristic methods do not satisfy Pfaff's condition (which needs to be satisfied for any mathematical relation to be valid). A mathematically consi...

The possible use of a simple methodology to study laser-beam propagation in a transonic flow and observe the aero-optical effects was investigated. The experimental setup consisted the DIRCM pod, the wind tunnel, and the image acquisition system. A steady-state CFD model of the experiment was developed using a commercial finite volume code. The num...

A power management system is introduced to control the current flow between a Polymer Exchange Membrane fuel cell and a Li-Ion battery. Depending on the load current and the battery state of charge, the power management system decides the amount of the load power shared with each power source. The hybrid system operating power is divided into three...

The aim of this work is to include the navigation step for the waypoint-based guidance of a UAV system and to illustrate aspects such as tracking of the reference trajectory under wind presence, while conserving total energy requirements. The mission is represented utilising graph theory tools. The mathematical modelling of an aircraft controlled b...

In this article, the fuzzy-hybrid modelling (FHM) approach is used and compared to the input–output system Takagi–Sugeno (TS) modelling approach which correlates the drivetrain power flow equations with the vehicle dynamics. The output power relations were related to the drivetrain bounded efficiencies and also to the wheel slips. The model relates...

An experimental investigation of the effects of varying flapping kinematics on the mean lift produced by an insect-like flapping wing in hover is presented. This was performed with application to flapping-wing micro-air vehicles (FMAVs) in mind. Experiments were accomplished with a first-of-its-kind mechanical flapping-wing apparatus capable of rep...

This chapter provides an introduction to Volume 5, Part 22. It introduces some basic concepts of flight control, and static and dynamic stability. Some particular features of vertical or short take-off and landing (V/STOL) aircraft flight control, not covered elsewhere in this part, are discussed briefly. The other chapters in this part are introdu...

An experimental investigation was performed to observe the effects of Reynolds number and stroke amplitude (number of degrees swept over a half stroke) on the leading-edge vortex (LEV) of an insect-like flapping wing in hover. This was performed with application to flapping-wing micro air vehicles (FMAVs) in mind. Experiments were accomplished with...

Deceleration rate and terrain adhesive coefficient are critical factors, which are drastically diminishing the regenerative energy enhancement in the hybrid electric vehicle. In addition to that, sizing the electric propulsion system also very important to increase the acceleration performance and regenerative braking efficiency. For example, overs...

Unmanned aerial vehicle (UAV) electric propulsion is a modern aviation concept that has long endurance capacity compared to the conventional IC engines. The polymer exchange membrane (PEM) fuel cell and Li-Ion battery hybrid power plant shows a great potential to replace the IC engines from UAVs due to high energy and power densities of the power s...

An experimental investigation of the effects of planform shape on the flow structures generated by an insect-like flapping wing in hover are presented.This was performed with application to flapping-wing micro air vehicles (FMAVs) in mind.Experiments were accomplished with a first-of-its-kind mechanical flapping-wing apparatus capable of reproducin...

Intelligent power management (IPM) strategy is presented to control the fuel cell (FC)/battery-powered hybrid unmanned electrical aerial vehicle propulsion system. The IPM system shares the propulsion power demand between two power sources, by allowing the FC system to operate in maximum net power output. The IPM system, which manages FC system pow...

Insect-like flapping flight offers a power-efficient and highly manoeuvrable basis for micro air vehicles for indoor applications. Some aspects of the aerodynamics associated with the sweeping phase of insect wing kinematics are examined by making particle image velocimetry measurements on a rotating wing immersed in a tank of seeded water. The wor...

In this paper, flow control effectiveness of a passive device in relation to open cavity flowfield is investigated computationally and compared with experimental work. Specifically the modification in the cavity flowfield due to the presence of a spoiler is studied in details to explain the physics behind the flow control effects. A combination of...

A computational fluid dynamics study was performed to understand the effects of changing the upstream nozzle geometry on a rectangular free jet. A method is proposed, involving the formulation of an equation based upon a statistical model for a rectangular nozzle with an exit aspect ratio (AR e) of 4; the variables under consideration (for a consta...

Experiments and computations are presented for transonic flows over cavities having lengthto- depth ratios of 4. Front and rear end walls were yawed 15° and 30°, both parallel and staggered; 3 different saw-tooth spoilers were tested on the rectangular cavity upstream lip. Cavity tones were completely eliminated with 30o yawed walls or with the lar...

Intelligent power management (IPM) strategy is presented to control the fuel cell/ battery powered hybrid unmanned electrical aerial vehicle propulsion system. The IPM system shares the propulsion power demand between two power sources, by allowing the fuel cell (FC) system to operate in maximum net power output. The IPM system which manages the FC...

Fuel cell (FC)/ battery hybrid system power management is a decision making process which controls the power flow between each power sources. Intelligent power management (IPM) is an innovative power handling concept that can actively control the hybrid system power flow according to the load power changes and the battery state of charge variations...

Hybrid electric vehicle and electric vehicles are employing electric motor as one of the major propulsion medium. As a result of the higher performance requirement and to manipulate the variety of driving circumstances, sizing of the electric motor is crucial in this particular drivetrain systems. In addition to that, since the electric motor is as...

Because of their large operational potential, unmanned aerial vehicles (UAVs) may be required to perform over long periods of time, which might lead to potential degradation or even failure of their electrical or/and mechanical control surfaces and components. Consequently, the least failure can degrade the performance of the process and might lead...

This paper presents an investigation of a transonic flow (M(infinity) = 0.85) over a rectangular cavity having a length-to-depth ratio of 5. Velocities were measured inside the cavity on the central plane and two off-centre planes using a two-component particle image velocimetry system. These measurements were supported by surface flow visualizatio...

For a significant portion of the wingbeat cycle in insect-like flapping, the wing sweeps at more or less constant speed and angle of attack. The aerodynamics associated with this phase of insect-like wing kinematics are investigated by making 2D-2C particle image velocimetry measurements on a rotating wing immersed in a tank of seeded water. In an...

The interaction of multiple jets with the ground is of great importance for the design and operation of short takeoff, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry. Measurements were mad...

The aerodynamics of insect-like flapping are dominated by the production of a large, stable, and lift-enhancing leading-edge vortex (LEV) above the wing. In this paper the phenomenology behind the LEV is explored, the reasons for its stability are investigated, and the effects on the LEV of changing Reynolds number or angle-of-attack are studied. A...

The interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry and laser Doppler vel...

In this paper, the results of a computational study on the unsteady flow features in three-dimensional empty cavities and a cavity with a store are presented. Flow simula-tions with a turbulence model based on a hybrid method, which behaves as a standard RANS model within the attached boundary layer and as a LES Sub-Grid Scale model in the rest of...

The aerodynamic design of a flapping-wing micro air vehicle requires a careful study of the wing-design space to ascertain the best combination of parameters. Here, such wing design for hovering insectlike flapping flight is studied using a nonlinear unsteady aerodynamic model developed by the authors. The work is characterized, in particular, by t...

The aerodynamic design of a flapping-wing micro air vehicle requires a careful study of the wing design space to ascertain the best combination of parameters. A nonlinear unsteady aerodynamic model developed by the authors is used to make such a study for hovering insectlike flapping wings. The work is characterized, in particular, by the insights...

In this paper potential causes that lead to a failure are investigated through a digraph analysis utilizing graph theory tools and pseudo boolean expressions. A generic scenario of a multi-layered scheme for fault assessment for a UAV application, illustrates the proposed methodology. The resulting solution is obtained by the use of shortest path a...

In general, the minimum path problem is concerned with finding shortest paths between a start to an end node in the minimum distance sense. There are many interesting algorithms which may be utilized for that purpose, that fall under the category of the Euclidian travelling salesman problem [1] and [2]. Although these methodologies determine the op...

This paper presents power control strategies for the propulsion of unmanned arial vehicle (UAV) which is driven by fuel cell/battery hybrid system. UAV propulsion system has different power requirements in order to complete its mission successfully. The different power stages in propulsion system introduce in flight taxing, take off, cruising and l...

The interaction of multiple jets with the ground is of great importance for the design and operation of short take off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane, was studied using laser-based particle image velocimetry and laser Doppler ve...