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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Flash Freeze Flow Tube to Vitrify Aerosol Particles at Fixed Relative Humidity Values

Development of methods to measure the phase transitions and physical properties of submicron atmospheric aerosol particles is needed to better model these systems. Here, we introduce a method to flash freeze submicron particles to measure phase transitions as a function of relative humidity (RH). Particles are equilibrated at a fixed RH, vitrified in a temperature-controlled flow tube, and imaged with cryogenic transmission electron microscopy (cryo-TEM). We demonstrate the use of the technique for measuring the efflorescence relative humidity (ERH) of potassium sulfate and potassium chloride aerosol as well as the separation RH for a multicomponent organic/inorganic system that undergoes liquid-liquid phase separation (LLPS). The location of phase transitions can shift between the micrometer and nanometer size regimes and particles in a given population may have a range of RH over which a phase transition occurs. This technique addresses these requirements by allowing for characterization of the phase transitions for individual particles in a population on the submicron scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2000

Experimental Development and Physical Analysis of Jet and Vortex Actuators

The Vortex generator consists of a cavity with a lightweight actuator plate. The actuator plate acts like a piston pumping air out of the cavity on the down-stroke and sucking air into the cavity on the upstroke. The actuator is placed asymmetrically over the cavity opening, forming narrow and wide slots when viewed from the top. The actuator depending on amplitude, frequency, and slot spacing produces several flow fields (free jet, wall jet, vortex flow). Computational simulation of the actuator-generated flows have been developed and applied to several actuator flow modes. The objectives of this paper are to study the physics of the actuator-induced flow and to develop computational simulations of the actuatorgenerated flows. This work should provide an impetus for designing similar active flow control systems suitable for aircraft applications. The computational simulation uses a time-accurate full Navier-Stokes (NS) solver known as FTNS3D (a full NS version of CFL3D solver). A Multi-block moving grid has been developed and used for the computational study of the flow fields produced by the vortex generator. For three-dimensional computations, ten multi-block grids are used and for two-dimensional computations, six multiblock grids are used. The grid blocks adjacent to the actuator plate move with the plate motion, and second-order interpolation is used along the block interfaces. Periodic response of the flow has been observed to develop after three cycles of the plate sinusoidal motion.

Kandil, Osama A.↗
NASA NTRS2007

Experimental Evaluation of an Isolated Synthetic Jet IN Crossflow

The second case for this workshop builds upon the isolated synthetic jet of Case 1 by adding a crossflow, with no streamwise pressure gradient, for the developing jet to interact with. Formally, Case 2 examines the interaction of a single, isolated, synthetic jet and a fully turbulent zero-pressure gradient boundary layer. The resulting flow has many of the characteristics that need to be modeled with fidelity if the results of the calculations are to serve as the basis for research and design with active flow control devices. These include the turbulence in the boundary layer, the time-evolution of the large vortical structure emanating from the jet orifice and its subsequent interaction with and distortion by the boundary layer turbulence, and the effect of the suction cycle on the boundary layer flow. In a synthetic jet, the flow through the orifice and out into the outer flowfield alternates between an exhaust and a suction cycle, driven by the contraction and expansion of a cavity internal to the actuator. In the present experiment, the volume changes in the internal cavity are accomplished by replacing one of the rigid walls of the cavity, the wall opposite the orifice exit, with a deformable wall. This flexible wall is driven by a bottom-mounted moveable piston. The piston is driven electro-mechanically. The synthetic jet issues into the external flow through a circular orifice. In the present experiment, this orifice has a diameter of 0.250 inches (6.35 mm). The flow is conceptually similar to that documented in Schaeffler [1]. To document the flow, several measurement techniques were utilized. The upstream boundary conditions (in-flow conditions), and several key phase-averaged velocity profiles were measured with a 3-component laser-Doppler velocimetry system. Phase-averaged velocity field measurements were made with both stereo digital particle image velocimetry and 2-D digital particle image velocimetry as the primary measurement system. Surface pressure measurements were made utilizing an electronically scanned pressure system.

Schaeffler, Norman W.↗
DOE OSTI2018

Runtime Scheduling Policies for Distributed Graph Algorithms

In this paper we explore scheduling and runtime system support for unordered distributed graph computations that rely on optimistic (speculative) execution. Performance of such algorithms is impacted by two competing trends: the higher degree of parallelism enabled by optimistic execution in turn requires substantial runtime support. To address the potentially high overhead and scheduling complexity introduced by the runtime, we investigate customizable scheduling policies that augment the scheduler of the underlying runtime to adapt it to a specific graph application. We present several implementations of Distributed Control (DC), a data-driven unordered approach with work prioritization and demonstrate that customizable scheduling policies result in the most efficient implementation, outperforming the well-known -stepping Single-Source Shortest Paths (SSSP) and Jones-Plassmann vertex-coloring algorithms. We apply two scheduling techniques, flow control and adaptive frequency of network progress, which allow application-level control over the balance of domain work and the runtime work. Experimental results show the benefit of such application-aware scheduling for irregular distributed graph algorithms.

Firoz, Jesun S.↗
NASA NTRS2006

Minnowbrook V: 2006 Workshop on Unsteady Flows in Turbomachinery

This volume contains materials presented at the Minnowbrook V 2006 Workshop on Unsteady Flows in Turbomachinery, held at the Syracuse University Minnowbrook Conference Center, New York, on August 20-23, 2006. The workshop organizers were John E. LaGraff (Syracuse University), Martin L.G. Oldfield (Oxford University), and J. Paul Gostelow (University of Leicester). The workshop followed the theme, venue, and informal format of four earlier workshops: Minnowbrook I (1993), Minnowbrook II (1997), Minnowbrook III (2000), and Minnowbrook IV (2003). The workshop was focused on physical understanding of unsteady flows in turbomachinery, with the specific goal of contributing to engineering application of improving design codes for turbomachinery. The workshop participants included academic researchers from the United States and abroad and representatives from the gas-turbine industry and U.S. Government laboratories. The physical mechanisms discussed were related to unsteady wakes, active flow control, turbulence, bypass and natural transition, separation bubbles and turbulent spots, modeling of turbulence and transition, heat transfer and cooling, surface roughness, unsteady CFD, and DNS. The workshop summary and the plenary discussion transcripts clearly highlight the need for continued vigorous research in the technologically important area of unsteady flows in turbomachines. This volume contains abstracts and copies of select viewgraphs organized according to the workshop sessions. Full-color viewgraphs and animations are included in the CD-ROM version only (Doc.ID 20070024781).

LaGraff, John E.↗
DOE OSTI2023

Particle Flow Distribution in a Fluidized-Particles Multitube Solar Receiver

A fluidized-particles two-tube solar receiver was tested at ambient temperature at PROMES Laboratory to investigate the influence of an inhomogeneous solar flux density on the particle mass flow rate between the tubes. The principle of this 3rd generation solar receiver is to fluidize the particles in a container, called dispenser, in which the tubes’ bottom are immersed. The fluidized particles are flowing upward the tubes by applying an overpressure in the dispenser. Air velocities are changed inside the tubes, thanks to air mass flow controllers, to represent temperature heterogeneity between the tubes. Air velocities from 0.05 up to 0.52 m/s were tested, both in homogeneous and heterogeneous conditions. In the heterogeneous ones, the differences in air velocity between the tubes aim to mimic a difference in temperature from 20 to 100 % with homogeneous air flow rates injected. The following conclusions were drawn. First, the particle mass flux in the tubes are the same with homogeneous air velocities, each one following a calibration map previously obtained. Second, different air velocities lead to different particle mass flux. Third, the rise of the total particle mass flux diminishes the pressure in the dispenser. Four, this diminution of pressure leads to a decrease of the particle mass flow rate of the tube with the lower air velocity. This influence can lead in some cases to the stop of the fluidized bed circulation in the affected tube.

Sahuquet, Guillaume (ORCID:0000000302752890)↗
NASA NTRS1984

An inerference assessment approach for a three-dimensional slotted tunnel with sparse wall pressure data

The various procedures referred to as wall interference assessment and correction procedures presume the existence of a surface distribution of data (usually static pressure) measured over a surface on or near the tunnel walls for each test point to be assessed. An alternative approach in which a reasonably sophisticated computer model of the test section flow would be fitted parametrically to a sparse set of measured data is presented. The measurements provides line distributions of static pressure near the center lines of the top, side and bottom walls. The development of a test section model incorporating explicit recognition of discrete slots of finite length with controlled flow reentry into the solid wall downstream portion of the tunnel is shown.

Kemp, W. B., Jr.↗
NASA NTRS1999

Development of a flow feedback pulse duplicator system with rhesus monkey arterial input impedance characteristics

An in vitro pulsatile pump flow system that is capable of producing physiologic pressures and flows in a mock circulatory system tuned to reproduce the first nine harmonics of the input impedance of a rhesus monkey was developed and tested. The system was created as a research tool for evaluating cardiovascular function and for the design, testing, and evaluation of electrical-mechanical cardiovascular models and chronically implanted sensors. The system possesses a computerized user interface for controlling a linear displacement pulsatile pump in a controlled flow loop format to emulate in vivo cardiovascular characteristics. Evaluation of the pump system consisted of comparing its aortic pressure and flow profiles with in vivo rhesus hemodynamic waveforms in the time and frequency domains. Comparison of aortic pressure and flow data between the pump system and in vivo data showed good agreement in the time and frequency domains, however, the pump system produced a larger pulse pressure. The pump system can be used for comparing cardiovascular parameters with predicted cardiovascular model values and for evaluating such items as vascular grafts, heart valves, biomaterials, and sensors. This article describes the development and evaluation of this feedback controlled cardiovascular dynamics simulation modeling system.

Non-NASA Center↗
NASA NTRS2008

Scalability of Localized Arc Filament Plasma Actuators

Temporal flow control of a jet has been widely studied in the past to enhance jet mixing or reduce jet noise. Most of this research, however, has been done using small diameter low Reynolds number jets that often have little resemblance to the much larger jets common in real world applications because the flow actuators available lacked either the power or bandwidth to sufficiently impact these larger higher energy jets. The Localized Arc Filament Plasma Actuators (LAFPA), developed at the Ohio State University (OSU), have demonstrated the ability to impact a small high speed jet in experiments conducted at OSU and the power to perturb a larger high Reynolds number jet in experiments conducted at the NASA Glenn Research Center. However, the response measured in the large-scale experiments was significantly reduced for the same number of actuators compared to the jet response found in the small-scale experiments. A computational study has been initiated to simulate the LAFPA system with additional actuators on a large-scale jet to determine the number of actuators required to achieve the same desired response for a given jet diameter. Central to this computational study is a model for the LAFPA that both accurately represents the physics of the actuator and can be implemented into a computational fluid dynamics solver. One possible model, based on pressure waves created by the rapid localized heating that occurs at the actuator, is investigated using simplified axisymmetric simulations. The results of these simulations will be used to determine the validity of the model before more realistic and time consuming three-dimensional simulations are conducted to ultimately determine the scalability of the LAFPA system.

Brown, Clifford A.↗
NASA NTRS1976

Development of a fluidic rudder

Wind tunnel tests were performed to examine the concept of aircraft controls without moving parts, and aircraft stabilization by means of scoop-fed slots. Results of wind tunnel tests, in the framework of a NASA program, to determine the force-control characteristics of a symmetrical airfoil with scoop-fed slots are discussed. Further tests showed that a fluidic amplifier could be built into the airfoil and operate with ram air. A fluidic rudder was then developed, consisting of cascaded fluidic amplifiers necessary to couple low-level fluidic sensors with slot flow control of the aerodynamic force on the vertical tail.

Belsterling, C. A.↗
NASA NTRS2011

Spacecraft Radiator Freeze Protection Using a Regenerative Heat Exchanger

An active thermal control system architecture has been modified to include a regenerative heat exchanger (regenerator) inboard of the radiator. Rather than using a radiator bypass valve a regenerative heat exchanger is placed inboard of the radiators. A regenerator cold side bypass valve is used to set the return temperature. During operation, the regenerator bypass flow is varied, mixing cold radiator return fluid and warm regenerator outlet fluid to maintain the system setpoint. At the lowest heat load for stable operation, the bypass flow is closed off, sending all of the flow through the regenerator. This lowers the radiator inlet temperature well below the system set-point while maintaining full flow through the radiators. By using a regenerator bypass flow control to maintain system setpoint, the required minimum heat load to avoid radiator freezing can be reduced by more than half compared to a radiator bypass system.

Ungar, Eugene K.↗
NASA NTRS2011

Numerical Investigation of the Interaction of Counterflowing Jets and Supersonic Capsule Flows

Use of counterflowing jets ejected into supersonic freestreams as a flow control concept to modify the external flowfield has gained renewed interest with regards to potential retropropulsion applications pertinent to entry, descent, and landing investigations. This study describes numerical computations of such a concept for a scaled wind-tunnel capsule model by employing the space-time conservation element solution element viscous flow solver with unstructured meshes. Both steady-state and time-accurate computations are performed for several configurations with different counterflowing jet Mach numbers. Axisymmetric computations exploring the effect of the jet flow rate and jet Mach number on the flow stability, jet interaction with the bow shock and its subsequent impact on the aerodynamic and aerothermal loads on the capsule body are carried out. Similar to previous experimental findings, both long and short penetration modes exist at a windtunnel Mach number of 3.48. It was found that both modes exhibit non-stationary behavior and the former is much more unstable than the latter. It was also found that the unstable long penetration mode only exists in a relatively small range of the jet mass flow rate. Solution-based mesh refinement procedures are used to improve solution accuracy and provide guidelines for a more effective mesh generation procedure for parametric studies. Details of the computed flowfields also serve as a means to broaden the knowledge base for future retropropulsion design studies.

Venkatachari, Balaji Shankar↗
NASA NTRS2017

An Autonomous System for Experimental Evolution of Microbial Cultures: Test Results Using Ultraviolet-C Radiation and Escherichia Coli.

At its core, the field of microbial experimental evolution seeks to elucidate the natural laws governing the history of microbial life by understanding its underlying driving mechanisms. However, observing evolution in nature is complex, as environmental conditions are difficult to control. Laboratory-based experiments for observing population evolution provide more control, but manually culturing and studying multiple generations of microorganisms can be time consuming, labor intensive, and prone to inconsistency. We have constructed a prototype, closed system device that automates the process of directed evolution experiments in microorganisms. It is compatible with any liquid microbial culture, including polycultures and field samples, provides flow control and adjustable agitation, continuously monitors optical density (OD), and can dynamically control environmental pressures such as ultraviolet-C (UV-C) radiation and temperature. Here, the results of the prototype are compared to iterative exposure and survival assays conducted using a traditional hood, UV-C lamp, and shutter system.

Microbial Cultures↗
NASA NTRS2001

Innovative Airbreathing Propulsion Concepts for Access to Space

This paper will present technologies and concepts for novel aeropropulsion systems. These technologies will enhance the safety of operations, reduce life cycle costs, and contribute to reduced costs of air travel and access to space. One of the goals of the NASA program is to reduce the carbon-dioxide emissions of aircraft engines. Engine concepts that use highly efficient fuel cell/electric drive technologies in hydrogen-fueled engines will be presented in the proposed paper. Carbon-dioxide emissions will be eliminated by replacing hydrocarbon fuel with hydrogen, and reduce NOx emissions through better combustion process control. A revolutionary exoskeletal engine concept, in which the engine drum is rotated, will be shown. This concept has the potential to allow a propulsion system that can be used for subsonic through hypersonic flight. Dual fan concepts that have ultra-high bypass ratios, low noise, and low drag will be presented. Flow-controlled turbofans and control-configured turbofans also will be discussed. To increase efficiency, a system of microengines distributed along lifting surfaces and on the fuselage is being investigated. This concept will be presented in the paper. Small propulsion systems for affordable, safe personal transportation vehicles will be discussed. These low-oil/oilless systems use technologies that enable significant cost and weight reductions. Pulse detonation engine-based hybrid-cycle and combined-cycle propulsion systems for aviation and space access will be presented.

Whitlow, Jr., Woodrow↗
NASA NTRS2002

Adaptive Identification and Control of Flow-Induced Cavity Oscillations

Progress towards an adaptive self-tuning regulator (STR) for the cavity tone problem is discussed in this paper. Adaptive system identification algorithms were applied to an experimental cavity-flow tested as a prerequisite to control. In addition, a simple digital controller and a piezoelectric bimorph actuator were used to demonstrate multiple tone suppression. The control tests at Mach numbers of 0.275, 0.40, and 0.60 indicated approx. = 7dB tone reductions at multiple frequencies. Several different adaptive system identification algorithms were applied at a single freestream Mach number of 0.275. Adaptive finite-impulse response (FIR) filters of orders up to N = 100 were found to be unsuitable for modeling the cavity flow dynamics. Adaptive infinite-impulse response (IIR) filters of comparable order better captured the system dynamics. Two recursive algorithms, the least-mean square (LMS) and the recursive-least square (RLS), were utilized to update the adaptive filter coefficients. Given the sample-time requirements imposed by the cavity flow dynamics, the computational simplicity of the least mean squares (LMS) algorithm is advantageous for real-time control.

Kegerise, M. A.↗
NASA NTRS2009

Root Cause Assessment of Pressure Drop Rise of a Packed Bed of Lithium Hydroxide in the International Space Station Trace Contaminant Control System

The trace contaminant control system (TCCS) located in the International Space Station s (ISS) U.S. laboratory module employs physical adsorption, thermal catalytic oxidation, and chemical adsorption to remove trace chemical contamination produced by equipment offgassing and anthropogenic sources from the cabin atmosphere. The chemical adsorption stage, consisting of a packed bed of granular lithium hydroxide (LiOH), is located after the thermal catalytic oxidation stage and is designed to remove acid gas byproducts that may be formed in the upstream oxidation stage. While in service on board the ISS, the LiOH bed exhibited a change in flow resistance that leading to flow control difficulties in the TCCS. Post flight evaluation revealed LiOH granule size attrition among other changes. An experimental program was employed to investigate mechanisms hypothesized to contribute to the change in the packed bed s flow resistance. Background on the problem is summarized, including a discussion of likely mechanisms. The experimental program is described, results are presented, and implications for the future are discussed.

Aguilera, Tatiana↗
DOE OSTI2019

Functional compartmentalization in the hemocoel of insects

The insect circulatory system contains an open hemocoel, in which the mechanism of hemolymph flow control is ambiguous. As a continuous fluidic structure, this cavity should exhibit pressure changes that propagate quickly. Narrow-waisted insects create sustained pressure differences across segments, but their constricted waist provides an evident mechanism for compartmentalization. Insects with no obvious constrictions between segments may be capable of functionally compartmentalizing the body, which could explain complex hemolymph flows. Here, we test the hypothesis of functional compartmentalization by measuring pressures in a beetle and recording abdominal movements. We found that the pressure is indeed uniform within the abdomen and thorax, congruent with the predicted behavior of an open system. However, during some abdominal movements, pressures were on average 62% higher in the abdomen than in the thorax, suggesting that functional compartmentalization creates a gradient within the hemocoel. Synchrotron tomography and dissection show that the arthrodial membrane and thoracic muscles may contribute to this dynamic pressurization. Analysis of volume change suggests that the gut may play an important role in regulating pressure by translating between body segments. Overall, this study suggests that functional compartmentalization may provide an explanation for how fluid flows are managed in an open circulatory system.

Science & Technology - Other Topics↗
NASA NTRS1993

On the aerodynamics and performance of active vortex generators

As a building block in the development of smart lift-enhancement devices, a new concept for flow control using active vortex generators (AVGs) is presented. Ramp, wedge, and doublet wedge (Wheeler) VG configurations are investigated. The AVGs are designed to conform to the surface of the wing section at low alpha. As the section approaches the stall, they are deployed and accordingly, alpha(stall) and C(lmax) are increased. A qualitative analysis of the flow around the various VG configurations was conducted in a low speed wind tunnel at 1.6 ft/s and a Reynolds number of approximately 3400. The results demonstrate that ramp VGs produce vortices that have the longest distance at breakdown. The VGs were also applied to a 25-in. span, 8-in. chord NACA 4415 wing section. Optimization studies were conducted on the spanwise spacing, chordwise position, and size of statically deployed VGs. The test results demonstrate a 14-percent increase in C(lmax) while increasing alpha (stall) by up to 3.

Barrett, Ron↗