Steady Thrust Research Articles

Optimal propulsion efficiency for NACA0012 foils with asymmetries in motion: A hybrid approach using the Taguchi method and artificial neural networks

Optimal propulsion efficiency for NACA0012 foils with asymmetries in motion: A hybrid approach using the Taguchi method and artificial neural networks

A Computational Examination of Side-by-Side Rotors in Ground Effect

This study investigates the interactional aerodynamics of hovering side-by-side rotors in ground effect. The 5.5-ft diameter, three-bladed fixed-pitched rotors are simulated using computational fluid dynamics at a targeted 5 lb/ft2 disk loading. Simulations are performed using the commercial Navier–Stokes solver, AcuSolve ®, with a delayed detached eddy simulation model. Side-by-side rotors are simulated at two heights above the ground (H/D = 0.5 and H/D = 1), and with two hub–hub separation distances (3R and 2.5R). The performance of side-by-side rotors in ground effect (IGE) is compared to isolated rotors out of ground effect. Between the side-by-side rotors IGE, a highly turbulent mixing region is identified where the wakes of each rotor collide. The flow fountains upwards, as well as exits outwards (along a direction normal to a plane connecting the two rotor hubs) with fountaining between the rotors reaching up to 0.75D above the ground. As blades at H/D = 0.5 traverse the highly turbulent flow, strong vibratory loading is induced and a thrust loss is observed over the outboard sections between the rotors that is large enough to negate any nominal ground effect benefits inboard. Side-by-side rotors at H/D = 0.5 with 2.5R hub–hub spacing produce peak-to-peak thrust oscillations up to 16% of the steady thrust. Rotors placed higher, at H/D = 1 are positioned above the turbulent mixing flow and produce significantly lower vibratory loads. The spacing between rotors at H/D = 0.5 and 3R hub–hub separation allows strong vortical structures to develop between the rotors which move from side to side over multiple revolutions. When the vorticity moves closer to one of the rotors, it produces a greater lift deficit over the outboard region and a stronger vibratory loading. For rotors closer together, at H/D = 0.5 and 2.5R separation, the vortical structures between rotors are constrained to a more concentrated area and show less side-to-side drift.

Визначення впливу внутрішніх та зовнішніх факторів на розкид тяги двигунної установки, що складається зі зв'язки кількох двигунів

The thrust spread of a stand-alone rocket engine caused by external (the pressure and temperature of the propellant components at the engine inlet) and internal (spread in the geometry and operating conditions of the engine units and assemblies) factors is known from experimental tests or can be computed by a known procedure. As a rule, liquid-propellant propulsion systems (LPPSs) of launch vehicle lower stages include a cluster of several engines, whose thrust spread cannot often be determined from firing tests due to limited capabilities of bench equipment. The aim of this work is to develop an approach to determining the thrust spread of an LPPS comprising a cluster of two and more engines. For a multiengine propulsion system, this methodological approach also includes the development of a mathematical model of engine interaction in an LPPS and calculations of an LPPS startup at different combinations of spread in the external and internal factors in cases where the parameter spreads of all engines are both identical and different. For an LPPS with two engines and a common oxidizer feed pipeline, the paper gives an example of calculating the effect of external and internal factors on the thrust spread of each engine and the LPPS as a whole during an LPPS startup. . It is shown that the calculated spread of the 90 percent thrust (combustion chamber pressure) time lies in the range – 0.0917 s to +0.0792 s (engine 1) and –0.0941 s to +0.0618 s (engine 2). The calculated variations of the combustion chamber pressure (engine thrust) from its nominal value lie in the range –6.2 percent to +7.0 percent (engine 1) and -6.8 percent to +6.3 percent (engine 2). The calculated spreads of the 90 percent thrust time and the thrust for the LPPS as a whole are far smaller (about by 40 percent) and lie in the range – 0.0733 s to +0.0457 s for the time and – 4.8 percent to +4.8 percent for the thrust (about the nominal thrust). Using Pearson’s chi-squared test, an estimate is obtained for the goodness of fit of the anticipated theoretical distributions of the 90 percent thrust time spread and the steady thrust spread to the obtained statistical ones both for the two engines and for the LPPS as a whole.

The effects of surge motion on the dynamics and wake characteristics of a floating tidal stream turbine under free surface condition

In this paper, a Computational Fluid Dynamics (CFD) code is used to investigate the tidal stream turbine performance under free surface condition and with surge motion: amplitudes of 1/24–1/4 rotor diameter and period of 3–12 s. The CFD model is evaluated against experiments of a piled turbine in a circulating flume, providing a difference of only 1.46% at rated TSR. The unsteady power and thrust follow the sum of a constant (similar to steady), velocity-induced, and acceleration-induced terms. In all tests, the damping term for the power response is approximately 3 times the steady power coefficient (Cp ∼ 0.33), whilst for the thrust, 1.6 times the steady thrust coefficient (Cz ∼ 0.77). Ignoring the small acceleration-induced coefficient leads to negligible simulation errors. Taken together, augmenting the surge amplitude and frequency increases the time-averaged and fluctuation of the power and thrust coefficient. Significant high- and low-pressure areas form around the blade edges, in function of the resultant velocity (sum of induced and inflow term), promoting peak and cavitation effects. From the ecological perspective, the induced-velocity develops a toroidal vortex near the wake, then mixes with the hub and tip vortexes, and propagates streamwisely toward the free surface. This effect is more pronounced with the surge amplitude rather than period, thereby exacerbating the wake deficit, and the wake structure is more sensitive to the variation of surge period so the restriction on the oscillation frequency should be considered as a priority in the designing phase. In the future, it will be important to explore the effects of blockage and depth immersion to assess extreme functioning and cavitation effects.

Методика визначення впливу внутрішніх та зовнішніх факторів на розкид тяги рідинного ракетного двигуна при його запуску

Despite of the package of measures to adjust a liquid-propellant rocket engine (LPRE) to a specified operating regime, minimum acceptable spreads in the geometrical parameters and operating conditions of its units and assemblies steel remain. These internal factors together with external ones (the pressure and temperature of the propellant components at the engine inlet) govern the engine thrust spread. To provide an acceptable engine thrust spread according to the engine requirements specification, it is important to know the spread value as early as at the stage of off-engine tryout of the engine units and assemblies. The aim of this work is to develop a procedure for calculating the effect of external and internal factors on the LPRE startup thrust spread. This paper presents a procedure for determining the effect of internal and external factors on the LPRE startup thrust spread. The procedure includes the development of a mathematical model of engine startup that accounts for the maximum number of internal factors, the choice of internal factors that produce the maximum effect on the LPRE startup thrust spread, the choice of a method for specifying the external and internal factor spread, engine startup calculations at different combinations of external and internal factor spread values, engine thrust spread determination, determining the statistical and the theoretical distributions of the 90 percent thrust time spread and the steady thrust spread, and assessing their goodness of fit using Pearson’s chi-squared test. The paper gives an example of calculating the effect of the external and internal factor spread on the LPRE startup thrust spread for a staged-combustion oxidizer-rich sustainer LPRE. Using the results of previous calculations, 12 internal factors that produce the maximum effect on the engine startup thrust spread are identified. It is shown that the calculated spread of the 90 percent thrust (combustion chamber pressure) time lies in the range – 0.08220s to +0.07300s about its nominal value, and the calculated steady engine thrust (combustion chamber pressure) spread lies in the range –6.4 percent to +6.6 percent of the nominal thrust. Using Pearson’s chi-squared test, an estimate is obtained for the goodness of fit of the anticipated theoretical distributions of the 90 percent thrust time spread and the steady thrust spread to the obtained statistical ones.

Design and research of magnetically levitated testbed with composite superconductor bearing for micro thrust measurement

A high temperature superconducting (HTS) magnetically levitated testbed has been developed for the steady thrust measurement of miniature ion electrospray thruster. The structure of the testbed mainly consists of an HTS composite bearing, a magnetic shielding plate, an active electromagnetic brake and a laser displacement sensor. The steady thrust is described as a function of the equilibrium angle displacement of the floating frame. Furthermore, the mechanical behaviors of HTS composite bearing were studied via finite element simulation and experiments, which include the load capacity, levitation stiffness and background noise. The results show that the thrust testbed can keep in low noise and have a load capacity up to 4 kg. According to the ignition testing of the electrospray thruster, the thrust force of 25.2 was measured by the testbed, which is close to the design value of miniature ion electrospray thruster.

Experimental and numerical study of a 10MW TLP wind turbine in waves and wind

This paper presents tests on a 1:60 version of the DTU 10MW wind turbine mounted on a tension leg platform and their numerical reproduction. Both the experimental setup and the numerical model are Froude-scaled, and the dynamic response of the floating wind turbine to wind and waves is compared in terms of motion in the six degrees of freedom, nacelle acceleration and mooring line tension. The numerical model is implemented in the aero-elastic code Flex5, featuring the unsteady BEM method and the Morison equation for the modelling of aerodynamics and hydrodynamics, respectively. It was calibrated with the tests by matching key system features, namely the steady thrust curve and the decay tests in water. The calibrated model is used to reproduce the wind-wave climates in the laboratory, including regular and irregular waves, with and without wind. The model predictions are compared to the measured data, and a good agreement is found for surge and heave, while some discrepancies are observed for pitch, nacelle acceleration and line tension. The addition of wind generally improves the agreement with test results. The aerodynamic damping is identified in both tests and simulations. Finally, the sources of the discrepancies are discussed and some improvements in the numerical model are suggested in order to obtain a better agreement with the experiments.

A thrust balance for low power hollow cathode thrusters

A hanging thrust balance has been designed, manufactured and tested at the University of Southampton. The current design allows for direct steady thrust measurements ranging from 0.1 to 3 mN but this can be easily extended to measure thrust in a different range. Moreover the chosen balance design and the thrust measurement procedure allow for the cancellation of thermal drifts. The thrust balance was tested with a T6 hollow cathode thruster providing measurements with an uncertainty of about 9.7%. The thrust data were compared to those obtained with another direct thrust balance and they are in quantitative agreement—the maximum difference being only 6%.

Static characteristics of a bellows-type flow regulator for the thrust control of a liquid rocket engine

A novel bellows-type flow regulator was designed with the ability to maintain a steady thrust level and to adjust the thrust of a liquid rocket engine. The flow regulator showed good performance not only in maintaining the flow rate despite changes in the pressure difference across the flow regulator, but also in adjusting the flow rate in response to a changing shaft angle. A mathematical static model of the flow regulator was developed. A design criterion for ideal performance of the flow regulator was derived by theoretical analysis of the mathematical model. It was established that the main design parameters of the flow regulator affecting flow rate maintenance were the number and the width of ports in the 2nd throttle. The static characteristics predicted by the mathematical model show good agreement with experimental results, thus validating the mathematical model.

Impulsively started planar actuator surfaces in high-Reynolds-number steady flow

AbstractThe characteristics of unbounded flow past an impulsively started planar energy extracting device, such as a wind or tidal turbine, are studied theoretically, numerically and experimentally. The initial thrust on an impulsively started device, which can be more than double the steady thrust, is an important consideration for design and safe operation. The energy sink is modelled here as an ‘actuator surface’ which imposes a uniform pressure discontinuity in the fluid proportional to the square of the fluid speed normal to the surface, the fluid density, and a dimensionless resistance coefficient. The flow past the actuator is studied theoretically for the case of weak resistance using an unsteady model which recovers steady linear momentum theory in the limit of long time. For the case of strong resistance the flow is studied numerically using the point vortex method. Experimental measurements of thrust on a mesh towed through static water are compared to the numerical results and show good agreement. The thrust on an impulsively started device is estimated, for a typical installation, to fall to within 10 % of the steady value within ∼1 min. The numerical model is also used to simulate the gradual startup of a device, yielding estimates of the time constant necessary in a control system in order to reduce peak thrusts in practice.

Prediction Measurement of a Low-Frequency Harmonic Noise of Hovering Model Helicopter Rotor

Far-field acoustic data for a model helicopter rotor have been gathered in a large open-jet, acoustically treated wind tunnel with the rotor operating in hover and out of ground-effect. The four-bladed Boeing 360 model rotor with advanced airfoils, planform, and tip shape was run over a range of conditions typical of today's modern helicopter main rotor. Near in-plane acoustic measurements were compared with two independent implementations of classical linear theory. Measured steady thrust and torque were used together with a free-wake analysis (to predict the thrust and drag distributions along the rotor radius) as input to this first-principles theoretical approach. Good agreement between theory and experiment was shown for both amplitude and phase for measurements made in those positions that minimized distortion of the radiated acoustic signature at low-frequencies.

Hover Testing of Active Rotor Blade-Tips Using a Piezo-Induced Bending-Torsion Coupled Beam

This paper presents the development of an active on-blade vibration-reduction system using smart active blade tips (SABT), that are driven by a piezo-induced, bending-torsion coupled actuator. The actuator beam has a graphite substructure with surface bonded piezoceramic elements. A spanwise variation in both the bending-torsion coupling and the piezo element phasing is used to generate a pure tip twist. A small scale rotor, with 10% span active tips, was tested on the hover stand, at a reduced tip speed of Mach 0.25. At a mean thrust loading (CT/σ) of 0.07, and for an activation of 100 Vrms, SABT deflection amplitudes from 1.8 deg at 2/rev to 2.25 deg at 4/rev were achieved (half peak-to-peak). The rotor normal force measurements show a distinct coupling of the activation with the first and second flap frequencies of the rotor. The corresponding dynamic thrust, generated by a single active tip, relative to the steady thrust, ranges from 4.5% at 2/rev to 8.3% at 5/rev. For a 1/rev excitation, the single active tip generates a dynamic lift amplitude of 15% of the steady rotor thrust. The same actuator beam was used to test a rotor with controllable twist blades. The active twist blades used the same main blade section as the rotor blades with the active tips, and hence were not optimized for active twist configuration. Nonetheless, in hover, at a mean thrust loading (CT/σ) of 0.07, and with an activation of 100 Vrms, dynamic tip-twist amplitudes of 0.4 deg at 4/rev and 0.5 deg (at 5/rev) were achieved (half peak-to-peak).

Computer-aided Control Engineering Environments: Architecture, User Interface, Data-base Management, and Expert Aiding

Abstract Modern CAD environments for control systems engineering have begun to support substantial functionality beyond modeling, numerical analysis, and simulation. Three major areas that have emerged in the last five years are advanced interfaces, data-base management, and expert-systems support (expert aiding), In addition, there has been a steady thrust to integrate more completely the various functionalities and software that comprise computer-aided control engineering (CACE). These trends have produced CACE environments which have relatively modest improvements in numerical quality but a vastly different feel in terms of integration, support, and user friendliness. The basic considerations and requirements for a CACE interface (UI), data-base manager (DBM), and expert aicling are discussed in detail. In many cases, these will be illustrated by examples based on various CACE software suites including the new GE MEAD CACE environment; the basic thrust will be to define needs and show how these can be met. The GE MEAD Project involves the integration of powerful CACE packages under a supervisor which coordinates the execution of these packages with a modern UI, a CACE-oriented DBM, and an expert system. The interface is designed to facilitate access to the CACE package capabilities by users with widely different levels of familiarity with the environment. The data-base manager keeps track of system models that evolve over time and associates each analysis or design result with the correct model instance. The expert system supplies the machinery for expert aiding complicated or heuristic procedures to free the from low-level detail and tedium. This system thus exemplifies the trends mentioned above

Dynamic behavior of a 2-port pilot-operated solenoid valve for pneumatic use.

In this study, the dynamic behavior and operating condition of a 2-port pilot-operated solenoid valve were examined. The experiments were done by changing the upstream or the diameter of the pilot orifice. Steady or unsteady thrusts of the valve were analyzed by the control volume determined y the discharge chamber. From comparison of the experimental results with the calculated value, the following conclusions were obtained. The pressure p2o and p2s defined by eq. (5), (6) gave an indication of the design for the operation of the valve. As a time-lag response of p3, the characteristics of unsteady thrust which significantly affects the dynamic behavior of the valve is different from that of steady thrust. The dynamic behavior was considerably affected by the pressure distribution at the valve seat when the displacement of the valve was very small.

Numerical Prediction of Typical Articulated Rotor Impedance

The authors proposed a rotor impedance calculation procedure for articulated rotors in hovering and in forward flight, respectively, in Refs. 1 and 2. Sample calculations in these papers, however, used a rather simplified blade model, since the purpose was to show the essential characteristics of the rotor impedances. This paper conducts a more detailed numerical study of the rotor impedances for a typical articulated blade in practical use. The intent of this paper is to show that the detailed numerical analysis results in essentially the same characteristics as those obtained in Refs. 1 and 2 with a simplified blade model, and also that the effects of collective pitch on the impedances are not so significant in the practical articulated rotors. Contents I N the numerical calculations in Refs. 1 and 2, the chordwise center of gravity of the blade was assumed to be located on the elastic axis and that no elastic coupling existed between the flapwise bending, chordwise bending, and torsion. Moreover, when solving blade motion, a nonzero collective pitch, as well as a coning angle, were assumed in the generalized force calculations. Although this was done intentionally to estimate the effects of the steady thrust and the in-plane Coriolis force, it is inconsistent with the assumption of no elastic coupling. To remove these ambiguities, the exact mode shapes corresponding to each specific collective pitch setting are used with a consistent coning angle in the blade aeroelastic response calculations. The standard Holzer-Mykelstad method is used to conduct modal analysis. Major assumptions contained in the impedance analyses are: 1) The airloads are based on the linearized two-dimensional quasisteady theory and are integrated with the strip theory. 2) The effects of preceding and returning wakes are neglected. 3) The radial displacements of a blade are caused by the blade segments' flapping (around a steady coning) projected on a radial axis. 4) The blade spatial deformations are composed of / coupled natural modes (a total of /x3 modes), where / = 8 in this study. 5) The blade motions are represented in terms of the complex Fourier expansions of the generalized coordinates, and are truncated at the /zth harmonic, where h = 5 in this study. The H-34 helicopter rotor is selected as a sample. This is a four-bladed rotor having fully articulated rectangular blades of 28.0-ft radius and 1.366-ft chord. The spanwise characteristics are given in Ref. 3 in 18 spanwise segments.

Broadband and discrete frequency radiation from subsonic rotors

A unified analytical technique is presented for the prediction of both the discrete frequency and broadband acoustic signatures generated by aerodynamic rotors. While present applications deal with dipole (force) type radiation from circularly shaped source regions, the approach is formally applicable to other order multipoles and arbitrarily shaped source distributions. The prediction of broadband radiation from a hovering rotor due to inflow turbulence/blade interaction has been analyzed by using this approach. By working in co-ordinates fixed with respect to the observer rather than the blades, the appropriate blade-to-blade load correlations can be handled correctly. A direct relationship between the acoustic and turbulence spectra results. The most important parameter affecting the shape and magnitude of the acoustic spectrum is shown to be the ratio of the time taken by the rotor to complete one revolution to the time needed to convect one integral scale of turbulence through the rotor face. The result indicates no direct dependence of broadband noise on steady thrust level, except through whatever influence it may have on the mean velocity through the rotor face. The method is applied first to a simplified point dipole, quasi-steady aerodynamic blade model for a B -bladed rotor, providing a convenient upper bound estimate to the noise one can expect in a given situation. The principal effects of compressible unsteady aerodynamics and of distributed loading are analyzed and shown to result in reductions in high frequency radiation. The influence of chordwise distributed loading is found to be highly directional in nature, the radiation near the rotor plane being most affected. Comparisons between the present theory and the limited available experimental spectral data are presented, and exhibit reasonable agreement. It appears likely that some noise previously interpreted as discrete tones may actually be the result of interactions with large scale turbulence. Various means to effect reductions in turbulent interaction noise are discussed.