Human Performance Envelope Model Study Using Pilot’s Measured Parameters

Taking into consideration that nowadays the aerospace industry focuses a lot on safety, more durable and stable systems are developed. While the system itself is safer, there is another element that can have a high impact on the overall safety of a flight, namely the human factor. Pilot physiological parameters were measured during a full flight in a fixed cockpit environment using application-specific equipment. The recorded or calculated parameters are used to compute a performance envelope model with the scope of determining the degradation of the pilot’s condition during different flight phases or events. Several standardized tests were realized/performed on subjects who were given flight instructions before the test, without knowing beforehand the scenario and events that will occur/take place. This study helps in identifying the limits of pilots in different flight scenarios and the impact on their presumed performance.

Rotary Compressor Performance at Low Ambient Temperatures

Small rotary compressors are used in domestic heat pump appliances, for example, in domestic dehumidifiers and heat pump clothes dryers. Compressor performance curves provided by the manufacturer can be based on testing at relatively high ambient temperatures, in some cases as high as 35∘C. This can be much higher compared with the ambient temperature in which the compressor operates when, for example, it is installed in a domestic dehumidifier which can operate in ambient temperatures as low as 10∘C. We have developed a compressor calorimeter to test a small R134a rotary compressor extracted from a commercial domestic dehumidifier and use this to measure compressor performance parameters including the isentropic and volumetric efficiencies and the compressor heat loss fraction. The performance testing has been carried out at ambient temperatures 10∘C, 15∘C, 20∘C and 25∘C for a fixed relative humidity of 70% to compare how the compressor performance varies with the ambient temperature, and to determine how well the compressor performs outside of the performance envelope provided by the manufacturer. The results show that isentropic and volumetric efficiency of these small compressors is relatively insensitive to variation in ambient temperature, even outside of the performance envelope provided by the manufacturer. However, the compressor heat loss fraction can, on average, double from 15% to 30%, between operation at ambient 25∘C and ambient 10∘C. The data obtained in this work is used to construct compressor sub-models for certain ambient temperatures. We show how these sub-models can be used to improve a domestic dehumidifier model for operation at low ambient conditions within the evaporator frosting regime and good agreement is obtained between experimental and simulated data. The authors are not aware of a domestic dehumidifier model designed to work at ambient temperatures within the frosting regime.

Alcids ‘fly’ at efficient Strouhal numbers in both air and water but vary stroke velocity and angle

Birds that use their wings for ‘flight’ in both air and water are expected to fly poorly in each fluid relative to single-fluid specialists; that is, these jacks-of-all-trades should be the masters of none. Alcids exhibit exceptional dive performance while retaining aerial flight. We hypothesized that alcids maintain efficient Strouhal numbers and stroke velocities across air and water, allowing them to mitigate the costs of their ‘fluid generalism’. We show that alcids cruise at Strouhal numbers between 0.10 and 0.40 – on par with single-fluid specialists – in both air and water but flap their wings ~ 50% slower in water. Thus, these species either contract their muscles at inefficient velocities or maintain a two-geared muscle system, highlighting a clear cost to using the same morphology for locomotion in two fluids. Additionally, alcids varied stroke-plane angle between air and water and chord angle during aquatic flight, expanding their performance envelope.

Pipeline Compressors Dry Gas Seal Retrofits

Methane emissions are classed as one of the most important contributors to climate change. This greenhouse gas has a global warming potential 21 times that of Carbon Dioxide. In the Oil and Gas industry, pipeline compressor emissions have been identified as an important source of methane released into the atmosphere. Wet seals (oil seals) technology will not meet new targets being set for methane emissions. John Crane has therefore developed a new dry gas seal design with a significantly narrower cross section to allow historically high value compressor assets to continue to function without the need for extensive redesign or replacement. This dry gas seal has been specifically engineered to replace wet seals within older centrifugal pipeline compressors. The main reasons associated with conversion from wet seals to dry gas seals include: moving to non-contacting technology which reduces seal wear issues, reduced operating costs from removal of oil seal supporting systems including degassing equipment, lower energy consumption due to the shear losses associated with oil seals, reduced maintenance costs by having a simpler supporting system and less frequent routine maintenance, and reduced emissions. Wet seals are typically compact in nature and are therefore very flexible in how they can be installed into a compressor. Traditional dry gas seals occupy a larger cross-sectional footprint and therefore it was necessary to develop a brand new gas seal that can retrofit into the same cavity without the need for expensive and prohibitive machining of the compressor shaft or housing. The resulting gas seal design is significantly compact when compared to a standard gas seal, yet provides sealing at maximum pipeline compressor duties of up to 120barg and 100m/s. In order to create a compact seal, John Crane has significantly reduced the cross section of the rotating (mating) and stationary (primary) sealing faces. This change brings about an increased level of complexity associated with dry gas seal design. In-house FEA and CFD simulations have been used to optimize the seal design and groove patterns. Results documenting the extensive design and simulation activities will be presented to demonstrate effective separation of the sealing faces throughout the entire seal performance envelope. A number of tests were specifically designed to thoroughly validate the seal design by simulating compressor field conditions. The product has undergone a series of testing through its entire performance envelope for pressure, speed and temperature. Specific accelerated tests were also designed to replicate the seal lifetime. The paper will describe the test setup and present the validation results.