scholarly journals Deep space optical communications (DSOC) downlink simulation with varying PPM order

2021 ◽  
Vol 53 (10) ◽  
Author(s):  
Emmanuel Domfeh Aboagye ◽  
Shun-Ping Chen
Keyword(s):  
Power Level ◽  
Space Mission ◽  
Operating Conditions ◽  
Communication Link ◽  
Noise Power ◽  
Deep Space ◽  
Data Rates ◽  
Wide Range ◽  
Error Probabilities ◽  
Operating Points

AbstractDuring the course of a typical deep space mission like the Mars Earth mission, there exist a wide range of operating points, due to the different changes in geometry that consequently cause different link budgets in terms of received signal and noise power. These changes include distance range, Sun-Earth-Probe angle, zenith angle and atmospheric conditions. The different operating points, with different losses (background noise, pointing losses and atmospheric losses), lead to different capacities and data rates over the course of a typical deep space mission. Consequently, different engineering parameters are adjusted and optimized to combat some of these varying losses in order to get acceptable data rates and bit error probabilities. This is a useful reason to analyze and simulate various operating conditions that occur with the varying spatial orbital time periods of the resulting received signal power level, noise power level, capacity, data rates and bit error probabilities. This paper details results of simulations of typical deep space optical communication link operation.

scholarly journals Deep Space Optical Communications (DSOC) Downlink Simulation with Varying PPM Order

2021 ◽  
Author(s):  
Emmanuel Domfeh Aboagye ◽  
Shun-Ping Chen
Keyword(s):  
Power Level ◽  
Space Mission ◽  
Operating Conditions ◽  
Communication Link ◽  
Noise Power ◽  
Deep Space ◽  
Data Rates ◽  
Wide Range ◽  
Error Probabilities ◽  
Operating Points

Abstract During the course of a typical deep space mission like Mars Earth mission, there exist a wide range of operating points due to the different changes in geometry that consequently cause different Link Budgets in terms of received signal and noise power. These changes include: Distance Range, Sun-Earth-Planet Angle, Zenith Angle and Atmospheric conditions. The different operating points with different losses (background noise, pointing losses and atmospheric losses) lead to different capacities and data rates over the course of a typical Deep Space mission. Consequently, different engineering parameters are adjusted and optimized to combat some of these varying losses in order to get an acceptable data rate and bit error probabilities. This provides a good basis to undertake analysis and simulations of the various operating conditions that occur with the varying spatial orbital time periods on the resulting received signal power level, noise power level, capacity, data rates and bit error probabilities. This paper details results of simulations done in a typical Deep Space Optical Communication link operation.

Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

2018 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Klaus Helbig
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Time Step ◽  
Hot Air ◽  
Wide Range ◽  
Vortex Systems ◽  
Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

Modeling heavy-duty diesel engines using tabulated kinetics in a wide range of operating conditions

2020 ◽  
pp. 146808741989616 ◽  
Author(s):  
Qiyan Zhou ◽  
Tommaso Lucchini ◽  
Gianluca D’Errico ◽  
Gilles Hardy ◽  
Xingcai Lu
Keyword(s):  
Diesel Engines ◽  
Operating Conditions ◽  
Scalar Dissipation ◽  
Cylinder Pressure ◽  
Heavy Duty ◽  
Variable Model ◽  
Progress Variable ◽  
Wide Range ◽  
Heavy Duty Diesel ◽  
Operating Points

Fast and high-fidelity combustion models including detailed kinetics and turbulence chemistry interaction are necessary to support design and development of heavy-duty diesel engines. In this work, the authors intend to present and validate tabulated flamelet progress variable model based on tabulation of laminar diffusion flamelets for different scalar dissipation rate, whose predictability highly depends on the description of fuel–air mixing process in which engine mesh layout plays an important role. To this end, two grids were compared and assessed: in both grids, cells were aligned on the spray direction with such region being enlarged in the second one, where the near-nozzle and near-wall mesh resolution were also improved, which is expected to better account for both spray dynamics and flame–wall interaction dominating the combustion process in diesel engines. Flame structure, in-cylinder pressure, apparent heat release rate, and emissions for different relevant operating points were compared and analyzed to identify the most suitable mesh. Afterwards, simulations were carried out in a heavy-duty engine considering 20 operating points, allowing to comprehensively verify the validity of tabulated flamelet progress variable model. The results demonstrated that the proposed approach was capable to accurately predict in-cylinder pressure evolution and NO x formation across a wide engine map.

CONCEPT CONSIDERATIONS FOR A DEEP SPACE GRAVITY PROBE BASED ON LASER-CONTROLLED FREE-FLYING REFERENCE MASSES

2007 ◽  
Vol 16 (12a) ◽  
pp. 2297-2307
Author(s):  
ULRICH A. JOHANN
Keyword(s):  
State Of The Art ◽  
Space Mission ◽  
Laser Ranging ◽  
Communication Link ◽  
Deep Space ◽  
Radio Communication ◽  
Light Pressure ◽  
Small Test ◽  
Gravity Probe ◽  
Mission Operation

Concept considerations for a space mission with the objective of precisely testing the gravitational motion of a small test mass in the solar system environment are presented. In particular, the mission goal is an unambiguous experimental verification or falsification of the Pioneer anomaly effect. A promising concept is featuring a passive reference mass, shielded or well modeled with respect to nongravitational accelerations and formation flying with a rather standard deep space probe. The probe provides laser ranging and angular tracking to the reference mass, ranging to Earth via the radio-communication link and shielding from light pressure in the early parts of the mission. State-of-the-art ranging equipment can be used throughout, but requires in part optimization to meet the stringent physical budget constraints of a deep space mission. Mission operation aspects are briefly addressed.

scholarly journals Ion Engine and Hall Thruster Development at the NASA Glenn Research Center

2002 ◽  
Author(s):  
Matthew T. Domonkos ◽  
Michael J. Patterson ◽  
Robert S. Jankovsky
Keyword(s):  
High Power ◽  
Electric Propulsion ◽  
Power Level ◽  
Operating Conditions ◽  
Hall Thruster ◽  
Research Center ◽  
Central Feature ◽  
Beam Diameter ◽  
Deep Space ◽  
Number Of Customers

NASA’s Glenn Research Center has been selected to lead development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability. The NASA Hall thruster program currently supports a number of tasks related to high power thruster development for a number of customers including the Energetics Program (formerly called the Space-based Program), the Space Solar Power Program, and the In-space Propulsion Program. In program year 2002, two tasks were central to the NASA Hall thruster program: 1.) the development of a laboratory Hall thruster capable of providing high thrust at high power; 2.) investigations into operation of Hall thrusters at high specific impulse. In addition to these two primary thruster development activities, there are a number of other on-going activities supported by the NASA Hall thruster program. These additional activities are related to issues such as thruster lifetime and spacecraft integration.

scholarly journals Evaluating the Use of Leaned Stator Vanes to Produce a Non-Uniform Flow Distribution Across the Inlet Span of a Mixed Flow Turbine Rotor

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Richard Morrison ◽  
Stephen Spence ◽  
Sung In Kim ◽  
Thomas Leonard ◽  
Andre Starke
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Operating Point ◽  
Mixed Flow ◽  
Design Performance ◽  
Turbine Performance ◽  
Percentage Points ◽  
Wide Range ◽  
Turbine Rotors ◽  
Operating Points

Abstract Current trends in the automotive industry have placed an increased emphasis on downsized turbocharged engines for passenger vehicles. The turbocharger is increasingly relied upon to improve power output across a wide range of engine operating conditions, placing a greater emphasis on turbocharger off-design performance. An off-design condition of significant importance is performance at low turbine velocity ratios, since it is relevant to engine transient response and also to efficient energy extraction from pressure pulses in the unsteady exhaust flow. An increased focus has been placed on equipping turbochargers with mixed flow turbine rotors instead of conventional radial flow turbine rotors to improve off-design performance and to reduce rotor inertia. A recognized feature of a mixed flow turbine is the spanwise variation of flow conditions across the blade leading edge. This is a consequence of the reduction in leading edge radius from shroud to hub, coupled with the increasing tangential velocity of the flow due to conserved angular momentum as the radius decreases. The result is increasingly positive incidence toward the hub side of the leading edge. The resulting region of highly positive incidence at the hub produces separation from the suction surface and generates significant loss within the rotor passage. The aim of this study was to determine if the losses in a mixed flow turbine (MFT) could be reduced by the use of leaned stator vanes, which deliberately created a significant spanwise variation of flow angle between hub and shroud at rotor inlet, to reduce the positive incidence at the hub. The turbine performance with a series of leaned vanes was compared against that of a straight vane using a validated computational fluid dynamics (CFD) model. It was found that increasing vane lean improved turbine performance at all operating points considered. An increase of 3.2 percentage points in stage total-to-static efficiency was achieved at a key off-design operating point. Experimental testing of a set of leaned vanes and the baseline vanes confirmed the advantage of the leaned vanes at all operating points, with an increase in measured efficiency of 2.6 percentage points at the key off-design condition. Unsteady CFD models confirmed the same level of improvement at this operating point. The CFD and experimental results confirmed that the losses in an MFT can be reduced by the use of leaned stator vanes to shape the flow at rotor inlet.

scholarly journals Numerical analysis of the flow rig for UWS spray examination in exhaust system-relevant conditions

2021 ◽  
Author(s):  
Krzysztof Górka ◽  
Bartosz Kaźmierski ◽  
Łukasz Kapusta
Keyword(s):  
Gas Flow ◽  
Water Solution ◽  
Exhaust System ◽  
Operating Conditions ◽  
Flow Conditions ◽  
Spray Formation ◽  
Wide Range ◽  
Mass Flow Rates ◽  
Operating Points ◽  
Highly Uniform

In the present study, a flow rig with optical access intended for spray investigations in exhaust system-relevant conditions was analysed in terms of flow and temperature in the spray area using numerical simulations. The operation of the rig was examined for a wide range of exhaust mass flow rates, temperatures and various forms of UWS (urea-water solution) spray plumes. The locations of the injector and thermocouple were verified. Both conventional and flash-boiling injections were considered to assess the effect of the interaction of sprays with a gas flow. The results showed a highly uniform flow in the visualisation area, with only minor fluctuations near the walls. A similar observation was carried out for the temperature distribution. It was found that the extreme operating conditions caused substantial deformations of the spray plumes. However, the selected injector location allowed us to properly observe the spray formation regardless of the flow conditions. The study showed that the examined test rig enabled reliable spray investigations for a wide range of operating points.

Transient Power Operation of a Supercritical Carbon Dioxide Brayton Cycle

2017 ◽  
Author(s):  
Eric M. Clementoni ◽  
Timothy L. Cox ◽  
Martha A. King ◽  
Kevin D. Rahner
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Control Strategy ◽  
Power Level ◽  
Integrated System ◽  
Operating Conditions ◽  
System Response ◽  
Brayton Cycle ◽  
Wide Range ◽  
Supercritical Carbon

The Naval Nuclear Laboratory has been operating the Integrated System Test (IST) with the objective of demonstrating the ability to operate and control a supercritical carbon dioxide (sCO2) Brayton power cycle over a wide range of conditions. The IST is a two shaft recuperated closed sCO2 Brayton cycle with a variable speed turbine-driven compressor and a constant speed turbine-driven generator designed to output 100 kWe. This paper presents a thermal-hydraulic lead control strategy for operation of the cycle over a range of operating conditions along with predicted and actual IST system response to power level changes using this control strategy.

Experimental and Numerical Assessment of the Impact of Part-Span Connectors on Turbine Efficiency and Flow Field

2019 ◽  
Author(s):  
C. Brüggemann ◽  
M. Schatz ◽  
D. M. Vogt ◽  
F. Popig
Keyword(s):  
Flow Field ◽  
Detailed Comparison ◽  
Operating Conditions ◽  
Free Standing ◽  
Aerodynamic Loss ◽  
Turbine Efficiency ◽  
Numerical Assessment ◽  
Wide Range ◽  
The Impact ◽  
Operating Points

Abstract This study presents the results of measurements in an industrial steam turbine test rig operated at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) in Stuttgart, Germany. In order to ensure safe operation over a wide range of operating conditions the last and penultimate rotor blade rows of this turbine feature Part-Span Connectors (PSC). The PSC provide additional coupling and mechanical damping during operation, however, they present a major obstacle to the flow, thus causing additional aerodynamic loss. The focus of the present work is on the aerodynamic impact of the PSC on the flow field of the last stage. To capture this impact, an extensive measurement campaign over a wide range of operating points was performed using two last blade row configurations that are identical with regard to the blade design, except for the fact that one features free-standing blades while the second is equipped with PSC. A performance assessment of these two configurations based on detailed probe measurements and overall turbine efficiency is presented. Additionally, a detailed comparison of 3D CFD-results employing an equilibrium steam (EQS) model and a non-equilibrium steam (NES) model for both configurations is shown with good agreement to the test data. However, comparing the two models reveals major differences whenever there is condensation occurring close to the evaluation plane, thus the advantage of applying the NES model is presented.

scholarly journals A New Approach to the Description of the Off-Design Losses in Radial-Inflow Turbine Rotors

1993 ◽  
Author(s):  
M. Schölch
Keyword(s):  
Pressure Ratio ◽  
Operating Conditions ◽  
Wide Range ◽  
Ratio Speed ◽  
Design Behaviour ◽  
Nozzle Position ◽  
Satisfactory Approximation ◽  
Radial Inflow Turbine ◽  
Rotor Losses ◽  
Operating Points

The off-design behaviour of a radial-inflow turbine with pivotable nozzle vanes was measured. The turbine geometry is presented in figure 1. The losses produced in the rotor were determined over a wide range of operating conditions which were established by varying pressure ratio, speed of rotation of the rotor and the nozzle vane position. Loss correlations proposed by other authors were used to approximate the measured losses. All correlations were only able to fit the results for a single nozzle position. None of the equations used gave a satisfactory approximation for all the operating points investigated. Therefore a new way of describing the rotor losses is presented and a physical explanation for the new correlation is given.

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