Ad Henderson

Lab-on-a-Chip device with laser-patterned polymer electrodes for high voltage application and contactless conductivity detection

A laser-patterned microchip electrophoresis device with integrated polymer electrodes for DC high voltages and AC capacitively-coupled contactless conductivity detection was developed. Electrophoresis separations comparable to devices with metal electrodes were obtained, at approximately 20 times lower cost.

Drag force and surface roughness measurements on freshwater biofouled surfaces

The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m × 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.

The influence of turbulence on wake dispersion and blade row interaction in an axial compressor

The influence of free-stream turbulence on wake dispersion and boundary layer transition processes has been studied in a 1.5-stage axial compressor. An inlet grid was used to produce turbulence characteristics typical of an embedded stage in a multistage machine. The grid turbulence strongly enhanced the dispersion of inlet guide vane (IGV) wakes. This modified the interaction of IGV and rotor wakes, leading to a significant decrease in periodic unsteadiness experienced by the downstream stator. These observations have important implications for the prediction of clocking effects in multistage machines. Boundary layer transition characteristics on the outlet stator were studied with a surface hot-film array. Observations with grid turbulence were compared with those for the natural low turbulence inflow to the machine. The transition behavior under low turbulence inflow conditions with the stator blade element immersed in the dispersed IGV wakes closely resembled the behavior with elevated grid turbulence. It is concluded that with appropriate alignment, the blade element behavior in a 1.5-stage axial machine can reliably indicate the blade element behavior of an embedded row in a multistage machine.

Observations of Transition Phenomena on a Controlled Diffusion Compressor Stator With a Circular Arc Leading Edge

Laminar-turbulent transition behavior is studied near the leading edge of an outlet stator blade in a low-speed 1.5-stage axial-flow research compressor. The stator is a typical controlled diffusion design with a circular arc leading edge profile. Slow response surface pressure distribution measurements are compared with numerical predictions from the quasi two-dimensional flow solver, MISES. These both show a strong flow acceleration around each side of the circular arc, followed by a rapid deceleration near each blend point of the arc to the main surface profile. The relative magnitude of the localized overspeeds varies significantly over the wide range of stator flow incidence investigated. The unsteady boundary layer behavior on the stator is studied using a midspan array of surface-mounted hot-film sensors. On the suction surface, wake-induced transitional and turbulent strips are observed to originate close to the leading edge. The boundary layer approaches separation near the leading edge blend point on the suction surface, but this does not always lead to localized turbulent breakdown or continuous turbulent flow: a significant portion of the flow on the forward part of the surface remains laminar between the wake-induced transitional strips. At high positive incidence the wake-induced transitional strips originate near the leading edge blend point, but their growth is suppressed by the strong flow acceleration. On the pressure surface, a small separation bubble forms near the leading edge blend point resulting in almost continuous turbulent flow over the whole incidence range studied.

Compressed air energy storage: Thermodynamic and economic review

Compressed air energy storage (CAES) is one of the most promising mature electrical energy storage (EES) technologies. In this paper, recent technological and thermodynamic advances in CAES are examined. This review includes an examination of the three major thermodynamic approaches to CAES, an overview of air and thermal storage systems, and an examination of CAES in a distributed application. An economic analysis is then offered in order to determine the commercial viability of this technology.

Unsteady Transition Phenomena at a Compressor Blade Leading Edge

Wake-induced laminar-turbulent transition is studied at the leading edge of a C4-section compressor stator blade in a 1.5-stage axial compressor. Surface hot-film sensor observations are interpreted with the aid of numerical solutions from UNSFLO, a quasi-three dimensional viscous-inviscid flow solver. The passage of a rotor wake, with its associated negative jet, over the stator leading edge is observed to have a destabilizing effect on the suction surface boundary layer. This leads to transition closer to the stator leading edge than would have occurred under steady flow conditions. The strength of this phenomenon is influenced by the rotor-stator axial gap and the variability of individual rotor wake disturbances. A variety of transition phenomena is observed near the leading edge in the wake path. Wave packets characteristic of Tollmien-Schlichting waves are observed to amplify and break down into turbulent spots. Disturbances characteristic of the streaky structures occurring in bypass transition are also seen. Examination of suction surface disturbance and wake-induced transitional strip trajectories points to the leading edge as the principal receptivity site for suction surface transition phenomena at design loading conditions. This contrasts markedly with the pressure surface behavior, where transition at design conditions occurs remotely from leading-edge flow perturbations associated with wake chopping. Here, the local receptivity of the boundary layer to the wake passing disturbance and turbulent wake fluid discharging onto the blade surface may be of greater importance.

The Influence of University Entry Scores on Student Performance in Engineering Mechanics

Abstract An ongoing study into the causes of poor student performance in engineering mechanics has uncovered some intriguing data on the relationships between students’ university entry scores and their performance in engineering mechanics courses. Statistical analysis has shown that the expected correlations between this key measure, used to determine students eligibility for study, and engineering mechanics score either do not exist or are too weak to base educational interventions on. However, students’ entry scores have instead been shown to provide a “risk factor”, whereby students’ risk of failing the subject can be determined by entry score ranges. The tracking of changes in risk factors may be used to gauge the effectiveness of educational developments in the delivery of engineering mechanics.

The influence of bacteria-based biofouling on the wall friction and velocity distribution of hydropower pipes

Abstract Algae biofouling due to freshwater diatoms has been investigated thoroughly in open channel flows. Their presence has been shown to cause a significant increase in the local skin friction coefficient, the overall drag coefficient and can produce reductions in flow capacity of up to 10%. This study extends previous work to investigate bacteria-based biofouling that forms on the inside walls of pipelines and machinery that are not exposed to direct sunlight. The effect of biofouling on a 1.5 m long internally painted pipe section of diameter 101.6 mm was investigated. The pipe section was installed in a hydropower scheme for an extended period to allow the growth of flow conditioned biofilms at an average flow velocity of U = 1.3 ms-1. The pipe section was tested over a range of Reynolds numbers under fully-developed turbulent conditions. At each flow rate the head loss of the fouled pipe was measured as well as the complete velocity profile at the downstream end of the pipe to ensure the full effect of the biofouling was captured. These results were used to evaluate the pipe friction factor and sand equivalent surface roughness. Trends in the experimentally determined values of pipe friction factor with varying Reynolds number are significantly different from those predicted by empirically-based theory. Experimental velocity profiles show significant deviations from the theoretical prediction of flow through a rough pipe, with a higher maximum velocity observed in the centre of the pipe but a lower velocity in the near wall region.

A Comparative Investigation of Round and Fan-Shaped Cooling Hole Near Flow Fields

This study presents velocity and turbulence data measured experimentally in the near field of a round and a laterally expanded fan-shaped cooling hole. Both holes are fed by a plenum inlet, and interact with a turbulent mainstream boundary layer. Flow is Reynolds number matched to engine conditions to preserve flow structure, and two coolant to mainstream blowing momentum ratios are investigated experimentally. Results clearly identify regions of high shear for the round hole as the jet penetrates into the mainstream. In contrast, the distinct lack of high shear regions for the fan shaped hole point to reasons for improvements in cooling performance noted by previous studies. Two different CFD codes are used to predict the flow within and downstream of the fan shaped hole, with validation from the experimental measurements. One code is the commercially available ANSYS CFX 10.0, and the other is the density-based solver with low Mach number preconditioning, HYDRA, developed in-house by Rolls-Royce plc for high speed turbomachinery flows. Good agreement between numerical and experimental data for the center-line traverses was obtained for a steady state solution, and a region of reversed flow within the expansion region of the fan-shaped hole was identified.

Separation and Relaminarization at the Circular Arc Leading Edge of a Controlled Diffusion Compressor Stator

This paper investigates the influence of Reynolds Number and incidence on boundary layer development at the leading edge of a controlled diffusion (CD) stator blade with circular arc leading edge profile. Steady flow measurements were made inside a large scale 2D compressor cascade at Reynolds numbers of 260,000 and 400,000 for a range of inlet flow angles corresponding to both positive and negative incidence. Detailed static pressure measurements in the leading edge region show the time-mean boundary layer development through the velocity overspeed and following region of accelerating flow on the suction surface. Separation bubbles at the leading edge of the pressure and suction surfaces trigger the boundary layer to undergo an initial and rapid transition to turbulence. On the pressure surface, the bubble forms at all values of incidence tested, whereas on the suction surface a bubble only forms for incidence greater than design. In all cases the bubble length was seen to reduce significantly as Reynolds number is increased. These trends are supported by surface flow visualization results. Quasiwall shear stress measurements from hot-film sensors were interpreted using a hybrid threshold peak-valley-counting algorithm to yield time-averaged turbulent intermittency on each blade surface. These results in combination with raw quasi-wall shear stress traces show evidence of boundary layer relaminarization on the suction surface, downstream of the leading edge velocity overspeed in the favorable pressure gradient leading to peak suction. The relaminarization process is observed to become less effective as Reynolds number and inlet flow angle are increased. The boundary layer development is shown to have a large influence on the total blade pressure loss. At negative incidence, loss was seen to increase as Reynolds number is decreased, and in contrast at positive incidence, the opposite trend was displayed.