Patrick Hendrick

Acute Exposure to Diesel Exhaust Impairs Nitric Oxide–Mediated Endothelial Vasomotor Function by Increasing Endothelial Oxidative Stress

Exposure to diesel exhaust was recently identified as an important cardiovascular risk factor, but whether it impairs nitric oxide (NO)–mediated endothelial function and increases production of reactive oxygen species (ROS) in endothelial cells is not known. We tested these hypotheses in a randomized, controlled, crossover study in healthy male volunteers exposed to ambient and polluted air (n=12). The effects of skin microvascular hyperemic provocative tests, including local heating and iontophoresis of acetylcholine and sodium nitroprusside, were assessed using a laser Doppler imager. Before local heating, skin was pretreated by iontophoresis of either a specific NO–synthase inhibitor (L-N-arginine-methyl-ester) or a saline solution (Control). ROS production was measured by chemiluminescence using the lucigenin technique in human umbilical vein endothelial cells preincubated with serum from 5 of the subjects. Exposure to diesel exhaust reduced acetylcholine-induced vasodilation (P<0.01) but did not affect vasodilation with sodium nitroprusside. Moreover, the acetylcholine/sodium nitroprusside vasodilation ratio decreased from 1.51±0.1 to 1.06±0.07 (P<0.01) and was correlated to inhaled particulate matter 2.5 (r=−0.55; P<0.01). NO–mediated skin thermal vasodilatation decreased from 466±264% to 29±123% (P<0.05). ROS production was increased after polluted air exposure (P<0.01) and was correlated with the total amount of inhaled particulate matter <2.5 &mgr;m (PM2.5). In healthy subjects, acute experimental exposure to diesel exhaust impaired NO–mediated endothelial vasomotor function and promoted ROS generation in endothelial cells. Increased PM2.5 inhalation enhances microvascular dysfunction and ROS production.

Micropower generation with microgasturbines: A challenge

Abstract This paper describes the development of a microgasturbine with a rotor diameter of 20 mm. The target electrical power output lies around 1 kW. The total system fits in a cylinder with a diameter of 95 mm and a length of 120 mm. The system contains the same components as a large gasturbine generator: compressor, recuperator, combustion chamber, turbine, and electrical generator. Major challenges are the high rotational speed (500 000 r/min), high turbine inlet temperature (1200 K), and the efficiency of the components. Because of the small dimensions, the flow through compressor and turbine is characterized by relatively low Reynolds numbers. The higher flow losses and inherently lower efficiency require a higher blade tip speed (524 m/s) than for large turbines (300-400 m/s). To minimize wear and frictional losses, the rotor is mounted on aerodynamic bearings. To withstand the high centrifugal stresses, a high-strength steel is used for compressor and shaft. The turbine is made of a Si3N4-TiN ceramic composite to withstand the combination of elevated stress and temperature.

Wind tunnel testing of a VTOL MAV propeller in tilted operating mode

This paper presents experimental results of the full 3-axis force vector and 3-axis moment vector acting on a propeller, commonly used for a Vertical Take Off and Landing Micro Aerial Vehicle (VTOL MAV). Measurements were carried out in a wind tunnel using a high resolution 6-axis force/moment sensor embedded in a customized test rig at several wind speeds, propeller rotational speeds and angles of the propeller shaft with respect to the air stream. Results show strong moments acting on the propeller in forward flight and unstable conditions in descending flight. Power calculations reveal a decrease in power consumption during slow forward flight and how motor efficiency can be maximized.

Study of a Two-Phase Flow Pump and Separator System

The Aero-Thermo-Mechanics (ATM) Department of ULB (Universit Libre de Bruxelles) is developing an original system to pump and separate a two-phase flow. Many applications need to extract a certain phase of a multiphase flow: oil extraction, flow in nuclear pumps, flow in aircraft lubrication systems, pulp and paper processing, etc. The main objective of this study is to obtain a lightweight, compact, and efficient system that can both extract the gas of a two-phase flow and increase the pressure of the liquid phase. Prototypes with different designs were first tested at ULB on a specific test bench using water and air. The current prototype is a kind of axial-centrifugal pump. The axial part is used to separate the two phases of the flow and to collect, in the centrifugal part, the liquid phase only. The test results of the water-air prototypes have allowed to identify the key design and working parameters for efficient separation and pumping. A theoretical model has also been developed to describe the behavior of these prototypes. After successful tests with water-air mixtures, the technology has been implemented for a hot oil-air mixture. The tests with oil-air mixtures are performed on the aeroengine lubrication system test bench that the ATM Department developed and continues developing for other projects. At the same time, the flow field in the pump and separator system is being studied with commercial computational fluid dynamics software packages. Several two-phase flow models are considered for this particular application.

Air-Hydrogen Heat Exchangers for Advanced Space Launchers

This paper deals with air-hydrogen heat exchangers intended to provide in-flight oxygen collection capability to a reusable or semireusable two-stages-to-orbit launcher with an oxygen collection phase in supersonic cruise at Mach 2.5. It aims to present a theoretical but mainly technological and experimental feasibility study of heat exchangers sufficiently efficient and reliable to suit the extreme requirements of this application. Two precoolers of two different types (shell and tubes, and plate and fins) have been selected and designed with the objective of fulfilling all constraints of the concept in terms of performance, leak tightness, reliability, compactness, etc. This design process has been validated with four subscaled breadboards (two of each type) tested on two test benches (for performance and leak tightness), developed by Belgium and Spain, in on-design and off-design conditions. All these results highlight the suitability of the new technologies given the extreme requirements of the concept. An optimum design for each technology is recommended considering its proper advantages and disadvantages. An innovative precooler technology is presented and tested.

Integration of vehicle, propulsion system and separation unit designs for a launcher using in-flight oxygen collection

The use of in-flight Oxygen Collection has shown to significantly improve space launcher performance. The conceptual approach followed by the Royal Military Academy of Brussels (RMA) has tried to widen the available design margins in order to reduce the required technological leap and limit the economical risk associated with such a development. The aim of the ESA-funded theoretical and experimental study on an air separation device is to demonstrate the possibility of performing efficient air distillation in a compact rotating column. An integration of the vehicle, propulsion system and separation unit designs is presented aiming to optimise the overall vehicle performance while keeping technological difficulty and system complexity at a reasonable level. Reference vehicles are presented in their specific mission profiles with an emphasis on TSTO’s. Different layouts of the internal energy and mass flowsheets are compared, in order to make best use of the refrigeration capacity of the hydrogen fuel running though the propulsion system during the first phase of the flight considering the separator as a classical distillation column. This analysis provides the requirements in terms of heat exchange capacity, compression ratios and number of so-called transfer units needed in the separator. Here, the system is intentionally kept simple, to limit complexity, but the analysis is thorough and accurate, including, for example, the effect of the presence of argon. An analysis of the separation unit to reach those requirements is proposed. That includes internals, practical building with estimates of pressure drop, separation performance and flow limitation. Analysis of size reduction of the distillation unit from usual 1-g column to the high-g unit is provided as well as the scale up methodology of laboratory results. First experimental results obtained with our centrifugally enhanced distillation separation system are presented and perspectives for a larger on-board operational unit proposed.

Preliminary Design of an ACES TSTO Air Launch Vehicle

This paper addresses a detailed preliminary design study of a twin fuselage semi-reusable TSTO launch vehicle. This double fuselage carrier, which would use hydrogen as a fuel, also collects the liquid oxygen (LOX), needed afterwards to propel the all-rocket orbiter. This collection takes place during an extended subsonic cruise phase that precedes the air launch of the orbiter. The concept of this 3 generation semi-reusable launch vehicle will be explained and the results from a detailed preliminary design with the AAA (Advanced Aircraft Analysis) software from Darcorp (USA) will also be given. The results for the aircraft weight distribution will be given as well as performance, aerodynamics and longitudinal stability indications for two reference missions. Besides that, the influence of the collection ratio obtained with the LOX collection plant upon the design of the launch vehicle is also addressed.

Structural Design Optimisation and Aerothermoelastic Analysis of LAPCAT A2 Mach 5 Cruise Vehicle

Structural design of hypersonic aircraft is highly affected by their non-conventional shapes and dimensions, and especially by the very high temperature loads encountered during flight. Indeed, compared to classical aircraft, the non-conventional configurations may lead to largely different internal structural stresses, and the temperatures would lead to high thermal stresses and a significant reduction in material strength and stiffness, resulting in innovative concepts. Moreover, the reduction in structural rigidity requires a stronger focus on aerothermoelastic deformations in the design and optimisation of the aircraft structure. This imposes the need for a closer coupling of the aerodynamic and structural tools than current practice. The current paper presents how the different sizing, analysis, design and optimisation tools are coupled in the design of the structure for the LAPCAT A2 vehicle and gives results of the optimisation of the A2 canard and wing. A wing structure with 6 spars and 6 ribs with cross-grid stiffeners, and a movable canard structure with 3 spars and 7 ribs and an ortho-grid stiffened skin lead to the lightest solutions. Buckling has been identified as the main weight driver for both cases, regardless of the number of ribs and spars used. The design and optimisation of the fuselage (ring frames, longerons and skin) is in progress. The aerothermoelastic module has also been implemented and applied successfully to the A2 wing, leading to the static aerothermoelastic solution after only 4 iterations.

New Approach of Gas–Liquid Computational Fluid Dynamics Simulations for the Study of Minimum Quantity Cooling With Airblast Plain-Jet Injectors

Due to the complexity of multiphase flows, they are often studied with numerical simulations. These simulations must be validated with experimental results. This paper introduces a new approach to initialize the continuous phase of gas–liquid flows generated by airblast nozzles for microlubrication applications with a recently modified commercial computational fluid dynamics (CFD) code FINE™/Open. Microlubrication is a technology used in metal machining where the coolant flow rate is lower than with conventional flood cooling. In this paper, single-phase gas and two-phase liquid–gas flows are studied. The continuous phase is simulated using Reynolds-averaged Navier–Stokes (RANS) equations coupled with a k–e turbulence model and the dispersed phase is simulated using a Lagrangian method. To validate these simulations, particle image velocimetry (PIV) and particle dynamics analysis (PDA) measurements have been performed. This study illustrates the possibility of performing complex two-phase simulations with the help of single-phase studies to initialize the continuous phase of the flow (i.e., the gas). The single-phase flow also helps in estimating the magnitudes of the droplet velocities.

Analysis of Minimal In-Flight Oxygen Collection Cycle for Two Stage Launchers

[Abstract] In the context of an ESA-funded study on an air separation device intended to provide in-flight Oxygen Collection capability to future launchers, experimental and system level investigations are performed. Formerly hosted by the Belgian Royal Military Academy, it is now sustained by the Universite Libre de Bruxelles. Looking at the world wide picture of space launcher studies, oxygen collection is seldom studied by space researchers and engineers. There are few really rational causes to this situation. Aerospace engineers are often reluctant to invest themselves in very different fields, which is strongly required here. Besides, the research projects are often cornered by funding constraints towards very high technology options. This often pushes resulting preliminary studies away from practically and economically viable new applications. To make design trades more accessible over such an heterogeneous set of concepts, simple models are required. The work provided here is the result of simplifying both the cycle, to limit technological constraints while retaining most of the performance, and to provide an approximate modelling while retaining a sensible analysis and sufficiently accurate predictions. The vehicle considered here has been presented in previous articles, but the result has a wider scope. Strong beneficial effects comes from combining the propulsion cycle of the first stage (possibly subsonic) with the separation process, leading to both oxygen collection and even improved propulsion efficiency for the first stage. This approach attempts to draw a reasonable bottom line for the separation plant performance and for the required system complexity. Simplified, but widely accepted, methods are presented for analysing the various aspects of the separation plant performance. Although the model has some drawbacks that can be corrected using a limited set of more accurate predictions, the mass and energy balance can be solved accurately. Options that have a strong impact on performance –mainly expressed by the collection ratioare analysed: use of significant hydrogen pressurisation and use of para-ortho conversion that improves cooling capacity of hydrogen. Although the system is brought to minimal complexity and some hydrogen capacity is wasted for system heat integration simplicity, the retained performance are found well within minimal requirements to sustain operation and are consistent with previous more accurate computations. The analysis therefore allows to assess a viable bottomline for the propulsion system complexity and technological level and to predict performance of oxygen collecting two stage to orbit vehicles with a rather simple analysis.