New wind tunnel facility for icing experiments on models of turbofan compressor surfaces

Compressors of modern turbofan engines are often sensitive to ice crystal accretion which can occur if aircraft fly through cloud regions associated with storm complexes. Such flight paths are occasionally necessary, and if ice accretion within the compressor does occur, the ensuing engine performance degradation can range from a mild reduction of effciency through to a complete loss of power. Many parameters influence the initiation and rate of ice accretion but the physical processes and parameters governing the sensitivity of compressor surfaces to ice accretion are not fully understood. To develop reliable engineering models that can be used to aid the design and operation of compressors under icing conditions, further experimental data is needed. Existing icing wind tunnels around the world are very capable, but the operating costs for these wind tunnels are typically very high. The objective of this work is to establish a new icing wind tunnel that has modest operating costs and yet can also facilitate hardware testing, instrumentation development, and fundamental studies of ice crystal icing at compressor-relevant flow conditions. A wind tunnel arrangement was proposed involving water droplet freeze-out using liquid nitrogen evaporation followed by natural particle melting through dilution with warm air. The viability of the arrangement was demonstrated theoretically using a conservation of energy analysis. Thermodynamic performance of the facility is dictated largely by the availability of the liquid nitrogen and the proposed operating concept specified using a maximum of 20 litre of liquid nitrogen per run in the facility within 2 minutes to achieve the target operating conditions for the facility: flow speed around 50 m/s, temperatures around 0 degrees C, and total water content up to 10 g/m3 with melting ratio up to 0.2. The hardware developed for the facility includes an icing jet generator with nozzle exit diameter of 170 mm, and an open circuit wind tunnel. Ice particles are generated by injecting water from atomiser nozzles into a mixture of recently-evaporated liquid nitrogen and air which provides a low-temperature medium for the freezing process. A liquid nitrogen receiver and valve system was designed to supply the liquid nitrogen into the evaporator at a metered and controllable rate. The suspended ice particle mixture is then delivered to a diffuser with perforated walls through which further air is injected for the purpose of raising the temperature of the mixture, and generating some natural melting of the ice particles. The icing jet nozzle contraction, which is attached to the downstream end of the diffuser chamber increased the flow velocity and decreased the non-uniformity of the flow velocity at the exit of the jet. The performance targets for the facility have mostly been achieved, and this has been confirmed through experimentation with individual components and with the facility working as a combined unit. Experimental results have demonstrated a generally favourable agreement with the energy equation analysis, and with results from Computational Fluid Dynamics (CFD) simulations. The probe traversing system developed for the icing jet nozzle exit flow enabled quantification of the velocity uniformity at the exit of the icing jet generator. Within a core flow diameter of 140 mm, the flow speed was 28.1±1.1 m/s. This speed is somewhat lower than the target figure of 50 m/s, but it is expected that this can be readily rectified through installation of a higher power blower. The jet exit temperature uniformity was also reasonable: over the same jet core flow region at one particular operating condition, the temperature was -9:1±1.9 degrees C. However, results from the isokinetic total water content probe developed for this work indicate that improvements in the uniformity of the water distribution are needed. Initial experiments with a 12.7mm diameter cylindrical test article have demonstrated some ice accretion at glaciated conditions, and more significant accretion was registered with a non-zero melting ratio operating condition. However, additional improvements are needed in the facility and in the instrumentation used to quantify the facility performance. The introduction of humidity control, melting ratio control, temperature control, and more extensive instrumentation having a faster-response time is achievable in the near term and is expected to have significant impact on the quality of data derived from the new icing wind tunnel in the near future

Microwave technique for liquid water detection in icing applications

The partial melting of ingested ice crystals can lead to ice accretion in aircraft compressors, but accurately measuring the relatively small fraction of liquid water content in such flows is challenging. Probe-based methods for detecting liquid water content are not suitable for deployment within turbofan engines, and thus alternatives are sought. Recent research has described approaches based on passive microwave sensing. We present here an approach based on active microwave transmission and reflection, employing a vector network analyzer. Utilization of both transmission and reflection provides additional data over and above emission or transmission only, and permits a more controllable environment than passive sensing approaches. The paper specifically addresses the question of whether such an approach is viable within the context of representative icing wind tunnel and engine flow conditions. A quasi-thermal equilibrium approach is presented herein to estimate the melting ratio during microwave analysis of samples at 0 °C. Experimental results using microwaves in the 2.45GHz region are presented, and post-processing methods investigated. This is followed by an investigation of detection limits for ice accretion in the sub-gram range. The results indicate the potential of the technique, with a number of avenues evident for further research

Interaction mechanisms for a laser-induced metallic boiling front

This thesis is about fundamental interaction mechanisms of laser remote fusion cutting, RFC, which is based on the formation of a quasi-stationary laser-induced boiling front that causes drop ejection, preferably downwards. Laser cutting of metals, invented in 1967, has developed from a niche to a well established high quality cutting technique in the manufacturing industry. Usually a gas jet is employed concentric to the laser beam, to eject the molten metal. One technique option, interesting though hardly applied yet because of usually low quality and speed, is remote laser cutting. Two techniques are distinguished, remote ablation cutting, grooving down through a sheet, layer-by-layer, and the here addressed remote fusion cutting, by a single pass through the sheet. For the latter, the ablation pressure from laser-induced boiling at the cutting front continuously accelerates and ejects the melt downwards. Advantages of remote laser cutting, facilitated by high brilliance lasers during the last decade, are the possibility of a larger working distance along with the avoidance of cutting gas and of a gas jet nozzle.   The review paper of the thesis surveys different laser remote cutting techniques, including their modelling, as well as the transition to keyhole welding, owing to similarities particularly from the boiling front and from root spatter ejection. The six Papers I-VI that compose the thesis address fundamental mechanisms of laser remote fusion cutting, theoretically and experimentally. In Paper I a simplified mathematical model of the RFC cutting front enables to estimate the geometrical and energetic conditions of the process. By evidence and post-modelling from high speed imaging, HSI, the simplified smooth cutting front model is developed further to a wavy topology in Paper III, for more sophisticated absorption analysis. As a systematic support, Paper II categorizes and analyses for the first time the different wavy topologies observed at the front, from HSI. The melt dynamics induced by a pulsed laser beam was studied in Paper IV, again from HSI. Apart from other interesting transient melt phenomena it was demonstrated that the ablation pressure can push the melt to a certain pending position during the laser pulse while the melt retreats by surface tension during the pulse break. To engage remote fusion cutting with additive manufacturing, Paper V introduces a novel technique where the drops ejected from RFC are transferred to a substrate, about a centimetre underneath, on which a continuous track forms. This technique can even be applied as an efficient recycling approach. In Paper VI a variant of the technique is presented, to develop a boiling front along the edge of a metal sheet from which the drop transfer takes place, in a different manner. This enables to systematically machine-off the entire sheet, which can be converted to a new shape and product.   Summarizing, the thesis provides a variety of analysis of fundamental mechanisms of a laser-induced boiling front that bear a certain simplicity and in turn controllability, of interest for established as well as for new applications, in manufacturing and in other sectors, including remote fusion cutting

A new wind tunnel facility for ice crystal icing experiments

The design and characterization of a new ice crystal icing wind tunnel facility is introduced through this work. The arrangement proposed in this work involves water droplet freeze-out using liquid nitrogen evaporation followed by natural particle melting through dilution with warm air. The viability of the concept was first demonstrated theoretically using a conservation of energy analysis. Thermodynamic performance of the facility is dictated largely by the availability of the liquid nitrogen, and in order to establish a facility with modest operating costs, the proposed operation specified using a maximum of 20 liter of liquid nitrogen per run with a maximum duration of two minutes. The target operating conditions for the facility were: flow speed around 50 m/s, temperatures around 0 ºC, and total water content up to 10 g/m3 with melting ratio up to 0.2. Experimental results have demonstrated a generally favorable agreement with the energy equation analysis, and with results from Computational Fluid Dynamics (CFD) simulations. Experiments have demonstrate sufficient uniformity of flow speed and temperature for the facility to be regarded as a viable wind tunnel for ice crystal icing experimentation. Although the measured flow speed was around 28 m/s, this can be readily increased to achieve the target condition in future work

Ethno-medicinal Survey for Some Wild Plants of Muzaffarabad, Azad Jammu & Kashmir, Pakistan

Wild plants have always held economic, nutritional and medicinal value for human beings. Present work is the study of local information of some wild plants being used for remedial purposes in District Muzaffarabad, Azad Jammu and Kashmir, Pakistan. The indigenous knowledge of local conventional uses was collected through survey and personal interviews during field trips. A total of 50 plant species were identified by taxonomic description using field guides and locally by medicinal knowledge of people living in the area. About 150 informers were interviewed randomly to record local names and ethno-medicinal uses of different plant species