Je Sargison

A Converging Slot-Hole Film-Cooling Geometry—Part 1: Low-Speed Flat-Plate Heat Transfer and Loss

This paper presents experimental measurements of the performance of a new film cooling hole geometry - the Converging Slot-Hole or Console. This novel, patented geometry has been designed to improve the heat transfer and aerodynamic loss performance of turbine vane and rotor blade cooling systems. The physical principles embodied in the new hole design are described, and a typical example of the console geometry is presented. The cooling performance of a single row of consoles was compared experimentally with that of typical 35° cylindrical and fan-shaped holes and a slot, on a large-scale, flat-plate model at engine representative Reynolds numbers in a low speed tunnel with ambient temperature main flow. The hole throat area per unit width is matched for all four hole geometries. By independently varying the temperature of the heated coolant and the heat flux from an electrically heated, thermally insulated, constant heat flux surface, both the heat transfer coefficient and the adiabatic cooling effectiveness were deduced from digital photographs of the colour play of narrowband thermochromic liquid crystals on the model surface. A comparative measurement of the aerodynamic losses associated with each of the four film-cooling geometries was made by traversing the boundary layer at the downstream end of the flat plate. The promising heat transfer and aerodynamic performance of the console geometry have justified further experiments on an engine representative nozzle guide vane in a transonic annular cascade presented in Part 2 of this paper [1].

A Converging Slot-Hole Film-Cooling Geometry: Part 2 — Transonic Nozzle Guide Vane Heat Transfer and Loss

This paper presents the first experimental measurements on an engine representative nozzle guide vane, of a new film-cooling hole geometry, a convergingslot-hole or console. The patented console geometry is designed to improve the heat transfer and aerodynamic performance of turbine vane and rotor blade cooling systems. These experiments follow the successful validation of the console design in low-speed flat-plate tests described in Part 1 of this paper. Stereolithography was used to manufacture a resin model of a transonic, engine representative nozzle guide vane in which seven rows of previously tested fan-shaped film-cooling holes were replaced by four rows of consoles. This vane was mounted in the annular vane ring of the Oxford cold heat transfer tunnel for testing at engine Reynolds numbers, Mach numbers and coolant to mainstream momentum flux ratios using a heavy gas to simulate the correct coolant to mainstream density ratio. Heat transfer data were measured using wide-band thermochromic liquid crystals and a modified analysis technique. Both surface heat transfer coefficient and the adiabatic cooling effectiveness were derived from computer-video records of hue changes during the transient tunnel run. The cooling performance, quantified by the heat flux at engine temperature levels, of the console vane compares favourably with that of the previously tested vane with fan-shaped holes. The new console film-cooling hole geometry offers advantages to the engine designer due to a superior aerodynamic efficiency over the fan-shaped hole geometry. These efficiency measurements are demonstrated by results from midspan traverses of a four-hole pyramid probe downstream of the nozzle guide vane.

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.

A Stochastic Fluid Flow Model of the Operation and Maintenance of Power Generation Systems

A tool to inform strategic decision making on electricity market bidding prices, based on prediction of long-term system operation, degradation, and maintenance, is described. The operation and maintenance of a hydro-power generation system is modeled using a bounded stochastic fluid flow model with special behavior at the boundaries. The stationary distribution for the model and useful time-dependent performance measures are derived. The application potential of the model is illustrated through a practical industry-derived example modeling the operation of a hydro-power generator, in which a number of operation strategies are compared using several performance measures.

Characterizing the roughness of freshwater biofilms using a photogrammetric methodology.

The physical roughness of a surface changes when freshwater biofilms colonize and grow on it and this has significant implications for surfaces enclosing water conveying systems such as pipelines and canals. Plates with surfaces initially artificially roughened with varying grit size were deployed in an open channel system and biofilms were allowed to grow on the exposed surface. The plates were retrieved at intervals in time and their surfaces mapped using close range photogrammetry. For a fine grit surface (0.5–4 mm particles), diatom-dominated biofilms initially grew between the roughness elements; they subsequently developed as a mat to create a physically smoother outer surface than the underlying rough surface. For a coarse grit surface (2–4 mm), biofilms colonized faster; in one instance, larger clumps of biofilm were observed as transverse ripples across the plate.

Numerical and experimental studies of the flow field in a cyclone dryer

The performance of a newly developed cyclone dryer is investigated using RANS-based single-phase computational fluid dynamics (CFD) and experimental model studies. The cyclone dryer is a cylindrical tower, divided by conical orifices into several chambers; recirculation of the flow within individual chambers ensures adequate retention time for drying of the transported solid material. Numerical calculations are performed using the commercial CFD code CFX5.7 for different mesh types, turbulence models, advection schemes, and mesh resolution. Results of the simulation are compared with data from experimental model studies. The RNG k- turbulence model with hexahedral mesh gives satisfactory results. A significant improvement in CFD prediction is obtained when using a second order accurate advection scheme. Useful descriptions of the axial and tangential velocity distributions are obtained, and the pressure drop across the cyclone dryer chamber is predicted with an error of approximately 10%. The optimized numerical model is used to predict the influence of orifice diameter and chamber height on total pressure drop coefficient.

DIATOM FOULING PROBLEMS IN A TASMANIAN HYDRO CANAL, INCLUDING THE DESCRIPTION OF GOMPHONEMA TARRALEAHAE SP. NOV.

Open air freshwater hydrocanals in Tarraleah, Tasmania, Australia, exhibit significant diatom biofouling which leads to economic losses in hydroelectricity generation. These fast-flowing (flow velocity 2 m s−1) canals produce between 2 and 18 tonnes dry weight of fouling and 1–5 mg chlorophyll a/m 2 over a 20 km long course, with the canal surface area being 192,000 m2. Mostly monospecific diatom communities of Tabellaria flocculosa occur in canal sections with reduced flow, whereas a stalk-forming (up to 200 μm long) Gomphonema species dominates the majority of canal fouling in fast flowing areas. Gomphonema tarraleahae Perkins et Hallegraeff is newly described, the species differing from its close relative, G. angustatum (Kützing) Rabenhorst in its extreme stalking habit and distinctive head and footpoles. Low numbers of G. subclavatum (Grunow) Grunow and two other undescribed Gomphonema species were also present in fouling. Seasonal changes in biofouling are most likely related to temperature (5–15°C annually) and light intensity variation, with shaded, south-facing walls exhibiting higher fouling densities. Implications for fouling mitigation strategies are discussed.

Design and Calibration of a Water Tunnel for Skin Friction Research

Abstract A new water tunnel facility has been designed for application in skin friction and boundary layer research. The closed loop, recirculating facility with working section 200 χ 600 χ 2400 mm and test surface 600 χ 1000 mm has been designed to operate at working section flow speeds of up to 2 ms-1 (Reynolds number based on test surface length 2.2 χ 106). A force balance enables the direct measurement of drag on test surfaces. Hot film, pitot and multi-hole pressure probes are used to investigate the near wall flow.

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.