Thrust Reduction Research Articles

Thrust Reduction of Magnetic Levitation Vehicle Driven by Long Stator Linear Synchronous Motor

The propulsion technology of long stator linear synchronous motors is used to drive high-speed maglev trains. The linear synchronous motor stator is divided into sections placed on guideway. The electric power supplies to stator sections in which the train just passes in change-step mode for long-distance operation. However, a thrust drop will be caused by change-step machinery for driving magnetic vehicle. According to the train speed and vehicle data, the change-step mode has three types of operation, namely premature commutation, simultaneous commutation, and late commutation. Each type of operation has a different thrust drop which can be affected by several parameters such as jerk, running speed, motor section length, and vehicle data. This paper focuses on determining the thrust drop of the change-step mode. The study results of this paper can be used to improve the operation system of high-speed maglev trains.

Smart control of fast ships – Part 1: A setup for automated proactive control of the thrust used to increase the operability of a small planing monohull sailing in head seas

While sailing in head or bow quartering seas, operators on board of small planing boats try to avoid unacceptably large vertical peak accelerations, the main limiting factor for operability, by temporary speed reductions. The operators observe the incoming wave, roughly estimate whether or not the next impact might be too severe, and if so, they choose a certain amount of thrust reduction. Results of full scale trials suggested that an increase of operability may be realised using this so-called thrust control. In this paper the concept of smart control for small planing monohulls sailing in head seas has been introduced. The idea of smart control is that a solution for the increase of the operability of small planing monohulls may be found by using automated proactive control of the thrust. The main purpose of smart control is to keep the vertical accelerations below a predefined threshold value while striving at the highest possible average forward speed during a trip. Three elements are essential for such a control system: a shipboard wave measurement system, a computational model that predicts the response and a stable control system for the thrust.

Analysis of dual secondary injection for thrust vectoring

PurposeThe purpose of this paper is to analyze the flowfield structure and performance of dual secondary injection system for thrust vectoring in a convergent‐divergent nozzle and to compare it with a single secondary injection system.Design/methodology/approachDual secondary injection for thrust vectoring in a convergent‐divergent nozzle is studied by solving three‐dimensional Reynolds‐averaged Navier‐Stokes equations by the means of Fluent. Realizable k‐ε turbulent model with enhanced wall‐treatment approach is used for viscous model. Density‐based solver and explicit scheme are employed in the computational model. In order to study the effect of injection location on the flowfield, distance between ports is considered as the key variable.FindingsResults show that under some circumstances, dual secondary injection system is more effective than a single injection system with the same mass flow rate. The study shows that when the distance between two ports is 8.5 times of the injection port's diameter (or more) and in the same time the first injection port is at least 1 throat diameter far from the nozzle throat, this system will show a better performance. In addition, this system reduces the probability of bow shock impingement to the opposite wall and consequently, the side force production has less limitation.Practical implicationsDual secondary injection for thrust vector control (SITVC) needs less secondary flow and therefore it makes less reduction in the primary thrust. It means that for a specific primary thrust, less mass fuel is needed which makes it more economic regarding the traditional SITVC systems.Originality/valueThe paper's value lies in using a three‐dimensional model to study the effect of two ports distance on SITVC performance and comparison among the performance of dual and single injections when there is an impingement.

Hybrid adaptive ascent flight control for a flexible launch vehicle

For the purpose of improving trajectory tracking performance of a launch vehicle under adverse flight conditions, this article describes the development of a hybrid adaptive ascent flight control architecture. The hybrid adaptive control approach augments linear feedback signals with contributions from both direct and indirect adaptive control elements. In addition, signal filters are incorporated into the feedback loop to prevent harmful interaction between the flight control system and structural bending modes. The performance of the hybrid adaptive flight controller is compared to that of a typical gain-scheduled linear feedback controller in a high-fidelity Ares I ascent simulator obtained from the NASA Marshall Space Flight Center. Results from simulations which consider nominal flight conditions show that the hybrid adaptive controller is able to maintain a tracking error magnitude that is comparable to or lower than its classical proportional–integral–derivative (PID) counterpart for the vast majority of the ascent phase. However, when a 10 per cent thrust reduction is applied to the first-stage rocket motor, the PID controller experiences significantly elevated error that diverges rapidly at the end of the simulation. In contrast, the hybrid adaptive controller steadily maintains a tracking error magnitude that is frequently 50 per cent or less of the corresponding PID value during the latter stages of ascent.

Mounting Troubles

This article analyzes the problems encountered in developing the first jumbo jet, the Boeing 747. In the 1960s, the jumbo jet—a wide-body aircraft with two aisles and up to 10 seats per row—was the logical next step in the progression of the airliner. For the Pratt & Whitney JT9D, which was causing the 747 trouble, the engine skin casing was both bending and ovalizing—exhibiting non-circular distortion—under thrust loading that could be as high as 43,500 pounds on takeoff. The ovalizing distortion resulted in turbine and compressor blade rubbing against the interior of the engine case and necessitated power-robbing increases in blade tip clearance gaps. The result was a serious reduction in thrust, and increased fuel consumption as much as 7 percent above guaranteed rates. Boeing chose to mount the JT9D engines well forward of the 747 wing leading edges. The successful resolution of ovalization problems encountered in mounting the JT9D to the first Boeing 747s has provided guidance for future installations of large fan commercial jet engines.

영구자석형 선형동기전동기의 단부효과에 의한 문제점 연구

A discontinuity of magnetic circuits according to the end effect is generated in PMLSM. And magnetic state of the 3 phase coils becomes unbalanced. Due to the unbalanced magnetic state, the unbalanced flux linkage, back electro-magnetic force and inductance of the 3 phase coils appear. In result, the circulating current is generated by unbalanced inductance even if the input voltages are in balanced state. Then the thrust and efficiency are decreased because of the circulating current. Therefore, in this paper, the unbalanced inductance and the thrust reduction according to discontinuity of magnetic circuits are analyzed by FEA(2D). To demonstrate the validity of the analysis results, the experiment results are compared with analysis results.

Numerical Analysis on Vibration Mitigation Effect of EPS Geofoam on Retaining Wall

The mitigation of earth force by placing expanded polystyrene (EPS) geofoam buffer between retaining wall and backfill soil under dynamic loading is a topic worth consideration. In this paper, the effects of EPS geofoam buffer on the reduction of thrust wall force are numerically studied to simulate three reduced-scale models of rigid walls using a large shaking table. Numerical simulation technique using the finite element program Abaqus is described. The paper shows that the numerical Abaqus models are able to capture the trend in earth forces with increasing base acceleration for all three models. The use of the EPS geofoam as a compressible buffer yields obviously reduction of the lateral seismic thrust against retaining wall. The quantitative dynamic load–time response of the numerical simulations was in good agreement with measured physical test values.

Helicopter Tail Rotor Thrust and Main Rotor Wake Coupling in Crosswind Flight

The tail rotor of a helicopter with a single main rotor configuration can experience a significant reduction in thrust when the aircraft operates in crosswind flight. Brown’s vorticity transport model has been used to simulate a main rotor and tail rotor system translating at a sideslip angle that causes the tail rotor to interact with the main rotor tip vortices as they propagate downstream at the lateral extremities of the wake. The tail rotor is shown to exhibit a distinct directionally dependent mode during which tail rotors that are configured so that the blades travel forward at the top of the disk develop less thrust than tail rotors with the reverse sense of rotation. The range of flight speeds over which this mode exists is shown to vary considerably with the vertical location of the tail rotor. At low flight speeds, the directionally dependent mode occurs because the tail rotor is immersed within not only the downwash from the main rotor but also the rotational flow associated with clusters of largely disorganized vorticity within the main rotor wake. At higher flight speeds, however, the tail rotor is immersed within a coherent supervortex that strongly influences the velocity field surrounding the tail rotor.

Jet Entrainment Theory for Vertical Takeoff and Landing Aircraft Suckdown

The suckdown induced on a vertical takeoff and landing aircraft by the lift jets and the equal but opposite reduction of jet thrust have been studied to develop a physics-based model for predicting these forces. Static pressure distributions and jet velocity profiles have been computed and compared to surface pressure and jet survey measurements to understand the origin ofthe forces on the aircraft and jet. It is concluded that the suckdown force on the aircraft in the absence of flow separation is caused by the acceleration of the flow entrained by the jet; this acceleration reduces the static pressure on the bottom of the fuselage more than on the top of the fuselage. The equal but opposite reduction of jet thrust is due to the increased loss of jet kinetic energy to turbulence in the high-pressure region created at the nozzle exit by the turning of the entrained flow. It is shown that both forces can be computed correctly if the static pressure at the nozzle exit is allowed to adjust to the local static pressure imposed by the entrained flow.

A Computational Investigation of Icing Effects on an S-Duct Inlet

The effects of a typical glaze ice accretion shape on the performance of the M2129 S-duct inlet are computationally investigated for a range of flight Mach numbers. A Reynolds-Averaged Navier-Stokes (RANS) code with k-o> turbulence model is used to simulate the compressible viscous flow in the S-duct inlet. The glaze ice accretion on the cowl lip is modeled on a steady-state basis from NASA LEWICE3D code. The results show that the total pressure recovery is reduced and the compressor face distortion level is increased with flight Mach number. A reduction of 22.8% in total pressure recovery is calculated for a flight Mach number of 0.85 in fully-developed glazed ice condition. The massive flow separations in the inlet induced by the glaze ice horn shapes also create a mass flow reduction in the inlet between 27 and 33% as compared to clean inlet for flight Mach numbers of 0.13 and 0.475, respectively. The combined effects of reduced total pressure recovery and the reduced mass flow rate results in a reduction of engine thrust between ~30 and 60% from low speed flight to Mach 0.85.

Performance and emission characteristics of biofuel in a small-scale gas turbine engine

Performance and emissions characteristics of a 30 kW gas turbine engine burning Jet A, soy methyl ester, canola methyl ester, recycled rapeseed methyl ester, hog-fat biofuel, and their 50% (volume) blends in Jet A were studied over a range of throttle settings. The addition of biofuel resulted in a reduction in static thrust and thrust-specific fuel consumption, and increased thermal efficiency. The CO and NO emissions from the turbine were reduced with the biofuel blends. The results suggest that an optimum mixture may be found that reduces pollutant emissions while producing the desired thrust. This study demonstrates that biofuels may serve as viable supplements to petroleum-based fuels.

Effects of incidence angle in bird strike on integrity of aero-engine fan blade

The possibilities of blade deformation and even fracture, the need for subsequent containment and reduction in thrust and power supply make bird strikes to aero-engine fan blades very serious events. Due to the different bird–plane flight paths and the different types of turbofan engines, the incidence angle between the bird and the engine fan blade can vary within a wide range. The present explicit non-linear three-dimensional finite-element analyses examine in detail the effect of the incidence angle when a canonical 4-lb bird strikes a typical engine fan blade, using the commercial code LS-DYNA. Both the bird and the blade are simulated in a Lagrangian framework. The homogenised fluidic constitutive equation of the bird follows the Brockman hydrodynamic model, while the blade is modelled as a viscoplastic material of the Perzyna type. It was found that normal incidence results in maximum impact forces and plastic strains leading to severe deformation. For the case in which the incidence angle is equal to or larger than 60°, the impact forces are significantly reduced, and the blade deformation remains within the elastic range. In addition, this work also provides a theoretical calculation for the bird Hugoniot pressure by assuming it as a high-speed soft-body impactor, thus providing a means for obtaining a quick conservative upper bound solution.

Experimental evaluation of azimuth thruster for tanker scale model with dynamic positioning system

Abstract The thrust-propeller shaft speed relationship is required to calibrate control parameters in order to perform experimental tests with dynamic positioning system (DPS) installed in the scale model. In general, actuators of a DPS are main propeller, side and azimuth thrusters and their characteristic curves are quite difficult to be obtained theoretically. Therefore, tests in laboratory are necessary to evaluate the performance of those propellers, so tests carried out with azimuth thruster with nozzle are presented. The focuses are twofold: the first one is to evaluate the bollard pull varying the propeller shaft speed and the azimuth angle, as well; the second purpose is to evaluate the thrust while the azimuth is swiveling. In order to do it, the thruster is installed in a captive container and forces and moments in horizontal plane are measured by the load and torque cells connected in a vertical beam. The preliminary bollard pull test results indicate some influence in the thrust due to the relative angle between the azimuth propeller and hull. Swiveling tests results show some thrust reduction in comparison to the bollard pull tests for the some azimuth angle and a difference between clockwise and counterclockwise is observed, albeit not relevant.

Impacts of low-pressure (LP) compressors’ fouling of a turbofan upon operational-effectiveness of a military aircraft

Some in-service deterioration in any mechanical device, such as an aircraft’s gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. As a result of experiencing deterioration (of the engine as a whole or any of its components individually), an engine will seek a different steady operating point relative to that for an engine with no deterioration. This results in changes in the available thrust from the engine(s) at the same TETs and/or rotational-speeds. Any reduction in the available thrust at specified engine settings, especially maximum available thrust from the engines, will have a significant adverse effect upon the aircraft’s operational-performance. These adverse effects can be reduced by having a better knowledge of the effects of each such deterioration on the aircraft’s operational-performance. Subsequently improvements can be made in the design and manufacture of adversely-affected components as well as in maintenance and repair practices. For a military aircraft’s mission-profile (consisting of several flight-segments), using a bespoke computer simulation, the consequences of low-pressure compressors’ fouling of a turbofan upon the aircraft’s mission operational-effectiveness have been predicted. This will help in making wiser management decisions, such as whether to remove the aero-engines from the aircraft for maintenance or to continue using them with some changes in the aircraft’s mission-profile, or planning different take-off times and/or carrying different fuel/weapon loads for aircraft with the various extents of low-pressure compressors’ fouling. Hence improved engine utilization and the optimal mission operational-effectiveness for a squadron of aircraft can be achieved.

Reduction of the lateral thrust of masonry arches and vaults with FRP composites

Fiber-reinforced polymer (FRP) composites are being increasingly used for rehabilitation and strengthening of masonry structures and, in particular, to strengthen masonry arches and vaults against their most critical failure mechanisms. The FRP reinforcement, introducing tension resistance, allows the line of thrust to fall outside the thickness of the arch. This fact has two important consequences: the capacity of the arch itself is increased, and the lateral thrust transmitted to the piers is reduced, thereby increasing the capacity of the “arch + piers” system. While the first effect has been stressed by existing research, less attention has been paid to the second effect, which nevertheless is very important for practical applications. In this paper, the effect of bonding an FRP sheet to the intrados of a circular arch on the minimum value of the lateral thrust is evaluated analytically. The model is then applied in particular to the four lateral arches of an edge vault. Edge vaults are a valuable part of the architectural and cultural heritage of some regions of Italy, and are structurally similar to cross-vaults except for the presence of a double-curvature shell portion in the middle of four barrel webs. These vaults are usually subjected to symmetric loading, as a result of the large dead-to-live load ratio. Hence, collapse of a vault typically occurs when no tie-rods or tie-beams are adopted and the piers are unable to bear the thrust of the vault. The paper also illustrates results of an experimental investigation on masonry edge vaults strengthened with FRP composites and subjected to uniform loading with measurement of the lateral thrust. Test results and theoretical predictions are presented and discussed.

06/00805 Lignite-water interactions studied by phase transition-differential scanning calorimetry: Fei, Y. et al. Fuel, 2005, 84, (12–13), 1557-1562.

Some in-service deterioration in any mechanical device, such as an aircraft’s gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. As a result of experiencing deterioration (of the engine as a whole or any of its components individually), an engine will seek a different steady operating point relative to that for an engine with no deterioration. This results in changes in the available thrust from the engine(s) at the same TETs and/or rotational-speeds. Any reduction in the available thrust at specified engine settings, especially maximum available thrust from the engines, will have a significant adverse effect upon the aircraft’s operational-performance. These adverse effects can be reduced by having a better knowledge of the effects of each such deterioration on the aircraft’s operational-performance. Subsequently improvements can be made in the design and manufacture of adversely-affected components as well as in maintenance and repair practices.For a military aircraft’s mission-profile (consisting of several flight-segments), using a bespoke computer simulation, the consequences of low-pressure compressors’ fouling of a turbofan upon the aircraft’s mission operational-effectiveness have been predicted. This will help in making wiser management decisions, such as whether to remove the aero-engines from the aircraft for maintenance or to continue using them with some changes in the aircraft’s mission-profile, or planning different take-off times and/or carrying different fuel/weapon loads for aircraft with the various extents of low-pressure compressors’ fouling. Hence improved engine utilization and the optimal mission operational-effectiveness for a squadron of aircraft can be achieved.

Optimization Design for Thrust Reverser Cascade with a View to Reduce Noise

reverser considered in this paper uses the natural blockage concept, with only the fan duct flow being reversed. This paper focuses on the study of the aerodynamic performance of the cascade within a cold stream thrust reverser. Aerodynamic simulations are carried out using realistic operating conditions, for idealized cascade models representing three design options. The aim of this work is to investigate whether the aerodynamic performance of the thrust reverser cascade has been improved while minimizing weight of the cascade. In addition, t1his is the first attempt of us to considering noise reduction during design of the thrust reverse. The numerical simulations show that despite a reduction in total reverse thrust for the weight reduced designs, the supersonic flow regime, which existed in the original design, was eliminated after changing vane configurations made with the 5% and 10% weight reductions. The aerodynamic performance around the cascade and in the fan duct within the thrust reverser has been improved. Moreover, the acoustic characteristics of the thrust reverser are improved too. The total reverse thrust is not significantly affected with the modified cascade.

Chisel edge and cutting lip shape optimization for improved twist drill point design

This paper investigates the optimization of twist drill point geometries in order to minimize thrust and torque in drilling. A point geometry parameterization based on the drill grinding parameters is used to ensure manufacturability of the optimized geometry. Three commonly used drill point geometries, namely, conical, Racon ® and helical, are optimized for drilling forces while maintaining the inherent characteristics of each of the profiles. A significant reduction is shown in the drilling forces for the optimized drills. Drills with the optimized conical point profile are produced and tests run to validate the reduction in thrust and torque.

Effects of Auxiliary Lift and Propulsion on Helicopter Vibration Reduction and Trim

This paper examines the vibration reductions caused by the introduction of auxiliary lift and propulsion, individually, as well as in combination, on a light [5800-lb (2640 kg)] helicopter with a four-bladed hingeless rotor, at flight speeds close to the maximum cruise velocity of the baseline helicopter. The changes in trim (vehicle orientations and control settings) because of auxiliary lift and propulsion are also examined in detail, and the fundamental mechanisms that produce the changes in trim and associated vibration reductions are identified. Based on results using a comprehensive aeroelastic analysis, it was concluded that auxiliary lift, alone, produces relatively small reductions in vibration. On the other hand, significant vibration reductions were obtained through auxiliary propulsion alone. A combination of lift and propulsion was most effective and reduced the vibration index by over 90%. It was also observed that auxiliary lift significantly reduces the main rotor thrust but increases the nose-down pitch attitude and tip-path-plane forward tilt to provide the required propulsive force. This increases the downwash through the rotor disk and requires a larger rotor longitudinal cyclic pitch input. In contrast, auxiliary propulsion that minimizes vibration produces little reduction in main rotor thrust, but results in a slightly nose-up pitch attitude (the auxiliary propulsion exceeds vehicle drag) along with a backward tilt of the tip-path plane. This decreases the downwash through the rotor disk and requires a smaller rotor longitudinal cyclic pitch input. A combination of auxiliary lift and propulsion minimizes vibration results in an even larger backward tilt of the tip-path plane and a net upwash through the rotor disk. The rotor collective pitch undergoes little change as a result of auxiliary lift, even though the main rotor thrust is decreased. In contrast, for auxiliary propulsion it decreases significantly even though the rotor thrust undergoes only small reductions. This counterintuitive observation is explained. The reduced downwash with auxiliary propulsion, or upwash with combined lift and propulsion, puts the rotor in a partial autorotation state, drastically reducing the induced drag, main rotor torque, and power. Auxiliary lift produces modest reductions in main rotor power, primarily because of a reduced profile drag associated with lower rotor loading. Because the rotor loading is lower with auxiliary lift than with auxiliary propulsion, but larger vibration reductions are produced with the latter, it can be deduced that vibration reductions are less a result of “unloading” of the rotor per se and more because of overall changes in trim, especially the reduction in longitudinal cyclic pitch (seen with auxiliary propulsion).

Facility Effects on Performance Measurements of Micropropulsion Systems that Utilize Gas Expansion

Facilities can affect the measurement of spacecraft propulsion system performance in a variety of ways. In this study an underexpanded freejet is used to simulate experimentally a micropropulsion system such as those thatoperate on the expansion of propellant gases through nozzle geometries. Facility effects on the thrust measured by a torsion thrust stand installed in two facilities with distinctly different characteristics have been quantified over a steady-state thrust range from 10 to 480 μN. The two facilities varied in dimension and pumping capacity with background pressures ranging from 10 - 6 to 10 - 4 torr. In both facilities the measured thrust decreased with increasing facility background pressure. At a thrust level of 10 μN, the thrust decreased by approximately 20% at a facility background pressure of 2 x 10 - 4 torr relative to the thrust measured at 2 x 10 - 6 torr; however, a similar background pressure only resulted in a 4% reduction in thrust at 120 μN. The larger percent decrease in measured thrust for a given background pressure in the low thrust range has implications for the design of micropropulsion test facilities. The facility background pressure effect contributes to less than 2% error for the thrust range from 10 to 480 μN at background pressures less than 10 - 5 torr, suggesting that low background pressures are necessary for accurate thrust measurements below 500 μN. An empirical formulation based on background-plume penetration theory provides estimates of the thrust degradation as a function of facility background pressure. The empirical model fits the experimental data reasonably well for jet centerline values of the background gas radius of penetration into the freejet plume.