Search Results

The flow around a circular cylinder is a classical problem of fluid dynamics, and its study is of great importance since the cylinder is one of the most commonly occuring shapes in engineering structures. The current experimental investigation examines both the mean drag and the unsteady flow parameters (in the form of a nondimensional eddy-shedding frequency) at critical, supercritical, and transcritical Reynolds numbers (Re > 3 × 105). The tests were conducted in the NASA Langley Low Turbulence Pressure Tunnel over a Reynolds number range of 2.5 × 105 to 6.2 × 106 and a Mach range of 0.05 to 0.40. The unsteady flow phenomena was measured in the wake and on the test section walls with miniature pressure transducers. The determination of the Strouhal number in the supercritical regime was complicated by the presence of broadband signatures in the frequency domain.

High capacity honeycomb panel heat pipes were investigated as heat rejection radiators on future space platforms. Starting with a remnant section of honeycomb panel measuring 3.05-m long by 0.127-m wide that was originally designed and built for high-efficiency radiator fins, features were added to increase thermal transport capacity and thus permit test evaluation as an integral heat transport and rejection radiator. A series of subscale panels were fabricated and reworked to isolate individual enhancement features. Key to the enhancement was the addition of a liquid sideflow that utilizes pressure priming. A prediction model was developed and correlated with measured data, and then used to project performance to large, space-station size radiators. Results show that a honeycomb panel with 5.08-cm sideflow spacing and core modification will meet the design load of a 50 kW space heat rejection system.

Variable pressure, variable displacement hydraulic pumps are described and their capability to increase the efficiency of advanced aircraft hydraulic systems is discussed. Potential methods of interfacing with the hydraulic system are also discussed and the dynamic response is analyzed.

A test program was initiated to study the effects of improved lubrication delivery on the total heat rejection of an aircraft accessory drive gearbox. The goal of this program was to reduce the overall gearbox heat rejection by minimizing the viscous drag and churning losses. The most practical heat sink available to secondary power subsystems on supersonic aircraft is the fuel supply; and due to its limited capacity, reduced heat rejection from these systems is very desirable. A model of gearbox cooling requirements will be presented and compared with the lube distribution of a baseline gearbox and subsequent modified configurations. The effects of oil-in temperature, and lube gallery pressure on heat rejection are shown, with emphasis placed on minimizing this heat rejection.

Hydrogen-air heat exchanger (HEX) and condensor in the engines with air precooling amount to, by various estimations, (in different schemes) 20-40% of total engine mass. The influence of some heat transfer increase methods on cooler mass and size is discussed. Atmospheric air cooling may result in frost formation on cooled surfaces and heat exchanger characteristics deterioration. The location of probable frost formation zones in different conditions may be determined by using two- dimensional mathematical model of heat exchanger. The model experimental study of frost formation was carried out. The quantitative parameters of this process are discussed. It was found that both reduction and increase of heat transfer may be obtained according to flow regime. Significant instability of flow with air condensation accompanied by large pressure pulsations was obtained. Methods to prevent the phenomenon are under study.

Aerodynamic effects induced from vectoring an exhaust jet are investigated using a well established thin-layer Reynolds averaged Navier-Stokes code. This multiple block code has been modified to allow for the specification of jet properties at a block face. The applicability of the resulting code for thrust vectoring applications is verified by comparing numerically and experimentally determined pressure coefficient distributions for a jet-wing afterbody configuration with a thrust-vectoring 2-D nozzle. Induced effects on the body and nearby wing from thrust vectoring are graphically illustrated.

A summary of an ESA/ESTEC sponsored technology research programme is given aiming at the development of a CO2 partial pressure sensor suitable for monitoring the PP CO2 inside the oxygen ventilation loop of the EVA life support module. At first, a trade-off of candidate sensor concepts is presented. As result, the infrared optical sensor concept has been selected. In the frame of a discussion on basic facts of IR absorption the rationale for the selected configuration of the IR sensor is given. A breadboard model of the PP CO2 sensor together with a test set-up has been established. The sensor was subjected to a test programme consisting of two separate test periods. The main results are given. Finally, the findings are discussed in the light of the development of future flight hardware.

A successful thermal storage system, useful in the 115 K to 120 K temperature range, has been designed and demonstrated in a typical IR sensor satellite environment. Because of its high heat of fusion, chemical stability, compatibility with aluminum, and its low room temperature vapor pressure, 2-methylpentane (2-MP) appeared to be the best phase change material (PCM ) in this temperature range. The pure material, however, exhibited severe supercooling that depresses the temperature at which freezing occurs by as much as 30 K below its normal 119.3 K freeze point, thereby making it totally unsuitable. Other hydrocarbons tested exhibited the same behavior. An extensive investigation found that supercooling was significantly reduced with the addition of 3% acetone which acts as a nucleation catalyst that aids crystallization.

Extensive development testing to support the design of the Space Station Freedom (SSF) Carbon Dioxide (CO2) Reduction Assembly (CReA) has been conducted. Both dual and single reactor eight-person capacity systems, supported by experimental test setups, have been used to broaden the design data base. Multiple catalysts were evaluated. Of significant importance was data that showed that operation of the Bosch reaction at elevated pressure 150-205 kPa (7-15 psig) provides significant increases in process efficiency. These improvements significantly reduce the recycle gas rate necessary to achieve a 99%+ CO2 reduction efficiency. Data presented illus-trates the improvements realized and defines the benefits that the new technology offers in terms of savings in power, weight and volume as illustrated by the SSF CReA.

A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested on the F-18 High Alpha Research Vehicle at the NASA Dryden Flight Research Facility. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports. The high-angle-of-attack flush airdata sensing system was calibrated and demonstrated using reference airdata generated by way of minimum variance estimation techniques which blended airdata measurements from two wingtip airdata booms with inertial velocities, aircraft angular rates and attitudes, precision radar tracking, and meteorological analyses. Calibration results are presented.

Hydraulic power requirements of military aircraft have increased significantly over the years. This has brought to the surface such issues as how best to manage the higher power requirements, which in many cases exist for only a small part of the duty cycle duration, and also how to minimize the system losses (heat rejection), which in turn can result in reduced cooling requirements. This paper summarizes some of the available data on the power requirements of military aircraft, discusses the inefficiencies of higher pressure systems being considered for high horsepower requirements, and describes the available approaches for better management of the high pressure/horsepower requirements, with respect to improving the operating efficiency of such systems.

In diesel engines with EGR and VGT, the gas flow dynamics has significant nonlinear effects. This is shown by analyzing DC-gains in different operating points showing that these gains have large variations. To handle these nonlinear effects, a nonlinear state dependent input transformation is investigated. This input transformation is achieved through inversion of the models for EGR-flow and turbine flow. It is shown that the input transformation handles the nonlinear effects and decreases the variations in DC-gains substantially. The input transformation is combined with a new control structure that has a pumping work minimization feature and consists of PID controllers and min/max-selectors for coordinated control of EGR-fraction and oxygen/fuel ratio. The EGR flow and the exhaust manifold pressure are chosen as feedback variables in this structure. Further, the set-points for EGR-fraction and oxygen/fuel ratio are transformed to set-points for the feedback variables.

Air Force Research Laboratory (AFRL) is pursuing development of advanced, distributed, intelligent, adaptive engine controls and engine health monitoring systems. The goals this pursuit are enhancing engine performance, safety, affordability, operability, and reliability while reducing obsolescence risk. The development of smart, high-bandwidth, high-temperature-operable, wide-range, pressure/temperature multi-sensors, which addresses these goals, is discussed. The resulting sensors and packaging can be manufactured at low cost and operate in corrosive environments, while measuring temperatures up to 2,552 °F (1,400 °C) with simultaneous pressure measurements up to 1,000 psi (68 atm). Such a sensor suite provides unprecedented monitoring of propulsion, energy generation, and industrial systems. The multi-sensor approach reduces control system weight and wiring complexity, design time, and cost, while increasing accuracy and fault tolerance.

Diesel fuel injection systems are operating at increasingly higher pressure (up to 250 MPa) with smaller clearances, making them more sensitive to diesel fuel contaminants. Most liquid particle counters have difficulty detecting particles <4 μm in diameter and are unable to distinguish between solid and semi-solid materials. The low conductivity of diesel fuel limits the use of the Coulter counter. This raises the need for a new method to characterize small (<4 μm) fuel contaminants. We propose and evaluate an aerosolization method for characterizing solid particulate matter in diesel fuel that can detect particles as small as 0.5 μm. The particle sizing and concentration performance of the method were calibrated and validated by the use of seed particles added to filtered diesel fuel. A size dependent correction method was developed to account for the preferential atomization and subsequent aerosol conditioning processes to obtain the liquid-borne particle concentration.

Calibration of internal combustion engines at different altitudes, above or below sea level, is important to improve engine performance and to reduce fuel consumption and emissions in these conditions. In this work, a flow test rig that reproduces altitude pressure variation is presented. The system stands out by its altitude range, compactness, portability and easy control. It is based on the use of turbomachinery to provide the target pressure to the engine intake and exhaust lines. The core of the system is composed of a variable geometry turbine (VGT) with a waste-gate (WG) and a mechanical compressor. Given a set of turbomachinery systems, the operation pressure and the air mass flow are controlled by the speed of the mechanical compressor and the VGT and WG position. A simple modification in the installation setup makes possible to change the operating mode from vacuum to overpressure. So that simulating altitude increase or decrease with the same flow test rig components.

The Exploration of Venus and the atmospheres of the giant planets is a part of NASA's program for Solar System Exploration which seeks to answer fundamental questions about the Solar System. The development of high specific energy supplies which can function at high temperature and high pressure is critical to the successful execution of this exploration. A primary need is power supplies that can function within the environment of the atmospheres of these planets and provide power to in situ measurement and imagery equipment. This includes instruments that can move on the surface or within the atmosphere to evaluate more than just point locations. An example of the conditions which may be encountered is provided in an analysis of the atmosphere of Venus which features an atmosphere of dense carbon dioxide covered with clouds of sulfuric acid aerosols, a surface temperature of 486°̠C and a surface pressure of 90 atmospheres. Mobile Energy Products Inc.

Aircraft generators are usually installed on an engine-mounted gearbox pad. In this type of installation, the speed range can be adjusted to match available generator speeds, and the installation environment is not as harsh as the engine operating environment. On the other hand, mounting the generator directly to the engine main shaft provides significant advantages, such as eliminating the generator gearbox pad, yielding major weight and cost savings. Furthermore, the low-pressure turbine spool might have excess power that could be used to power the generator, thus enhancing the overall engine performance. The obvious disadvantage is the hot environment inside the tail cone, which can exceed 700°F. In this installation, heat transfers to the generator by convection from the surrounding air, conduction through the mounting interface, and radiation from the 1200°F tail cone.

This technical paper will address advancements in automatic riveting machine design, control, and process. VME based motion control combined with new component designs have produced a very flexible, state of the art, riveting system. This flexibility allows use of the fully programmable squeeze/squeeze III slug process, and variable upper tooling clearance heights to decrease cycle times. This state of the art technology includes infinitely positionable high speed double acting servo pressure foot, drill and shave spindles, upper buck cylinder, lower ram, and lower clamp assemblies.

Resonance frequencies and the associated pressure amplifications of a typical hydraulic brake system have been studied. Solutions to suppress the pipeline natural frequencies and pressure amplifications were obtained. Preventing the natural frequencies of a brake hydraulic pipeline from matching with the landing gear natural frequencies would minimize landing gear related accidents and avoid brake hydraulic system performance at abnormal resonance conditions. Prevention of the matching frequencies will reduce the aircraft stopping distance.

The paper presents the results of the analysis of the simulation tests of the flow of fuel through the fuel rail for the designed radial aircraft engine. A 3D model has been developed for CFD calculations including the fuel rail and elements supplying the fuel to the injectors. Simulation tests were carried out using Star-CD software. The objective of simulation tests has been to determine flow characteristics of the fuel rail design. This design is atypical due to: the shape of the rail - a torus with internal diameter 630 mm, and the fuel flow rate of approximately 30 l/min. Analysis covered flow velocity and pressure at selected points of the design. The tests were conducted for two cases. The first covered constant fuel flow from all injectors; the second covered dynamic states that take place when the injector is opened. The purpose of these tests was to check the possibility of using this solution for prototype purposes.