Large Scale PIV for confined fires

Fire safety engineering, including knowledge of fire dynamics and fire-related hazards is crucial for securing people as well as rescue teams during interventions. One of the main critical aspects remains in determining the smoke dynamics at openings where fresh air and hot fumes mix. This particular phenomenon, encountered in many enclosures fires can reveal either well ventilated or under-ventilated fires. The response techniques of rescue teams are different depending on the ventilation status. Merci et al. (2016), Bengtsson et al. (2001) and Pretrel et al. (2012) have studied fire in enclosures that occur in oxygen-limited conditions. Generally, smoke dynamics are studied by using different devices or techniques. These include, among others, Pitot probes and bidirectional probes or McCaffrey probes, McCaffrey and Heskestad (1976). However, these probes are intrusive and potentially affecting the smoke dynamics. Moreover, only one-point data are evaluated. To overcome this difficulty, laser techniques such as PIV can be set up, see Tieszen et al. (2002) , Hou et al. (1996) or Koched et al. (2012). PIV technique has already been used in case of well-ventilated and under-ventilated fires conditions. A natural extension of this technique remains in applying the PIV technique close to the outlet of the container in order to highlight exchanges between hot exhaust fumes and fresh incoming air. The objectives of the paper remain threefold:1. First, we propose a specific design of enclosure fire to ensure large scale PIV measurements inside the enclosure.2. Second, the transition from ventilated to under ventilated fire conditions is evaluated

Inventive nesting behaviour in the keyhole wasp Pachodynerus nasidens Latreille (Hymenoptera: Vespidae) in Australia, and the risk to aviation safety

The keyhole wasp (Pachodynerus nasidens Latreille 1812), a mud-nesting wasp native to South and Central America and the Caribbean, is a relatively recent (2010) arrival in Australia. In its native range it is known to use man-made cavities to construct nests. A series of serious safety incidents Brisbane Airport related to the obstruction of vital airspeed measuring pitot probes on aircraft possibly caused by mud-nesting wasps, prompted an assessment of risk. An experiment was designed to determine the species responsible, the types of aircraft most affected, the seasonal pattern of potential risk and the spatial distribution of risk on the airport. A series of replica pitot probes were constructed using 3D-printing technology, representing aircraft with high numbers of movements (landings and take-offs), and mounted at four locations at the airport. Probes were monitored for 39 months. Probes blocked by mud nesting wasps were retrieved and incubated in mesh bags. Emerging wasps were identified to species. Results show that all nests in probes were made by P. nasidens, and peak nesting occurs in the summer months. Nesting success (as proportion of nests with live adult emergents) was optimal between 24 and 31°C and that probes with apertures of more than 3 mm diameter are preferred. Not all areas on the airport are affected equally, with the majority of nests constructed in one area. The proportion of grassed areas within 1000 m of probes was a significant predictor of nesting, and probe volume may determine the sex of emerging wasps.

Inventive nesting behaviour in the keyhole wasp Pachodynerus nasidens Latreille (Hymenoptera: Vespidae) in Australia, and the risk to aviation safety

The keyhole wasp (Pachodynerus nasidens Latreille 1812), a mud-nesting wasp native to South and Central America and the Caribbean, is a relatively recent (2010) arrival in Australia. In its native range it is known to use man-made cavities to construct nests. A series of serious safety incidents Brisbane Airport related to the obstruction of vital airspeed measuring pitot probes on aircraft possibly caused by mud-nesting wasps at prompted an assessment of risk. An experiment was designed to determine the species responsible, the types of aircraft most affected, the seasonal pattern of potential risk and the spatial distribution of risk on the airport. A series of replica pitot probes were constructed using 3D-printing technology, representing aircraft with high numbers of movements (landings and take-offs), and mounted at four locations at the airport. Probes were monitored for 39 months. Probes blocked by mud nesting wasps were retrieved and incubated in mesh bags. Emerging wasps were identified to species. Results show that all nests in probes were made by P. nasidens, and peak nesting occurs in the summer months. Nesting success (as proportion of nests with live adult emergents) was optimal between 24 and 31°C and that probes with apertures of more than 3 mm diameter are preferred. Not all areas on the airport are affected equally, with the majority of nests constructed in one area. The proportion of grassed areas within 1000 m of probes was a significant predictor of nesting, and probe volume may determine the sex of emerging wasps.

Experimentally Measured Effectiveness of Different Shroud Swirl Brake Profiles in a Centrifugal Compressor

As centrifugal compressors are pushed to operate at higher pressures and higher power levels, destabilizing gas forces often increase the challenge of designing a stable rotordynamic system. While technical innovations like damper seals, swirl brakes, and damper bearings that help stabilize compressors are numerous, predicting the impact that these improvements will have on a specific system is somewhat of an art form. To this end, researchers are constantly improving the depth of knowledge on these features so that the impact of these improvements is well defined. In the current work, the authors experimentally measured the impact of different swirl brake/vane concepts on the flow characteristics of a centrifugal compressor shroud cavity. The eye seal configuration studied here is a tooth on rotor labyrinth eye seal. The different shroud swirl vane geometries considered consist of various castellated features, each having the intent to reduce swirl velocity in the shroud cavity prior to entering the seal. The purpose of the testing was to determine whether a significant reduction in swirl velocity entering or exiting the seal could be measured with the different anti-swirl vane profiles over a conventional shroud cavity that was tested with the same setup. The metrics that determine the effectiveness of the swirl brake were based on upstream and downstream measurements of swirl velocity using pitot-probes at different depths in the shroud cavity, and measurements of seal exit angle and velocity using a traversing cobra-probe. The test data presented herein show definitively that the different swirl brake designs, including a slotted seal, a long vane, and a short vane, have a major impact on swirl velocities relative to the conventional shroud design. The most effective at reducing swirl entering/leaving the seal is the slotted seal, while the concepts employing shroud vanes were more effective at reducing swirl in the shroud cavity.

Numerical and experimental characterisation of an aeronautic Pitot probe

Aeronautic Pitot probes (PPs) are extremely important for airspeed and altitude measurements in aviation. Failure of the instrument due to clogging caused by ice formation can lead to dangerous situations. In this work, a commercial aeronautic PP was characterised experimentally regarding its inner composition, material properties and its thermal performance in a climatic wind tunnel. Performance runs were taken out in order to analyse the thermal response of the PP under various operating conditions with a particular emphasis on the cooling process in the case of a heating element failure. Data for the thermal conductivity, diffusivity and specific heat for each material forming the PP were obtained. A numerical model to simulate the thermal behaviour of the PP was created using Comsol Multiphysics (CM). Experimental data were compared with their numerical counterparts for model validation purposes. After the model was validated, the operation of the PP in flight conditions was simulated. The failure of the conventional heating system was analysed to obtain the time until the PP reaches a tip temperature where ice formation can be expected. The tip temperature undercut the zero degrees Celsius mark 165 seconds after the heating element was switched off. The data collected in this work can be used to implement and validate mathematical models in order to predict the thermal performance of Pitot probes in flight conditions.

Parasitic Loss due to Leading Edge Instrumentation on a Low Pressure Turbine Blade

During the testing of development engines and components, intrusive instrumentation such as Kiel head Pitot probes and shrouded thermocouples are used to evaluate gas properties and performance. The size of these instruments can be significant relative to the blades and their impact on aerodynamic efficiency must be considered when analysing the test data. This paper reports on such parasitic losses for instruments mounted on the leading edge of a stator in a low pressure turbine, with particular emphasis on understanding the impact of probe geometry on the induced loss. The instrumentation and turbine blades have been modeled in a low Mach number cascade facility with an upstream turbulence grid. The cascade was designed so that the leading edge probes were interchangeable in-situ, allowing for rapid testing of differing probe geometries. RANS calculations were performed to complement the experiments and gain more understanding about the flow behaviour. A horseshoe vortex-like system forms at the join of the probe body and blade leading edge, generating pairs of streamwise vortices which convect over the blade pressure and suction surfaces. These vortices promote mixing between the freestream and boundary layer fluid, and promote the transition of the boundary layer from laminar to turbulent flow. The size and shape of the leading edge probes relative to the blade varies significantly between applications. Tests with realistic probe geometries demonstrate that the detailed design of the shroud bleed system can impact the loss. A study of idealised cylinders is performed to isolate the impact of probe diameter, aspect ratio and incidence.