Thrust Prediction Research Articles

Computational fluid dynamics analysis of the vertical axis wind turbine blade with tubercle leading edge

The performance of a vertical axis wind turbine (VAWT) blade with NACA0015 airfoil section has been investigated using the commercial computational fluid dynamics software ANSYS FluentTM. The Semi Implicit Method for Pressure Linked Equations algorithm is chosen to solve the incompressible Navier-Stokes equations. The k-ω shear stress transport turbulence model was selected for the turbulence flow simulations. The simulation results of lift and drag coefficients between angles of attack of 0° and 40° were first validated with the experimental data in order to confirm the boundary layer distributions. The grid numbers and time step sizes were then examined to confirm the simulation accuracy. To exam the 3D effect, a 2.5D model was additionally developed and compared with 2D model. Finally, the predictions of thrust obtained from the blade with tubercle leading edge were compared with the ones from the straight blade. Overall, the thrusts of VAWT with modified turbine blades were lower than the ones with straight blade. The values of the thrust decreased with increasing amplitudes and decreasing wavelengths, mainly due to the structure of the vortices generated at the leading edge of the turbine blade.

An unsteady vortex lattice method model of a horizontal axis wind turbine operating in an upstream rotor wake

An unsteady formulation of the vortex lattice method, VLM, is presented that uses a force- free representation of the wake behind a horizontal axis wind turbine, HAWT, to calculate the aerodynamic loading on a turbine operating in the wake of an upstream rotor. A Cartesian velocity grid is superimposed over the computational domain to facilitate the representation of the atmospheric turbulence surrounding the turbine and wind shear. The wake of an upstream rotor is modelled using two methods: a mean velocity deficit with superimposed turbulence, based on experimental observations, and a purely numeric periodic boundary condition. Both methods are treated as frozen and propagated with the velocity grid.Measurements of the mean thrust and blade root bending moment on a three bladed horizontal axis rotor modelling a 5 MW HAWT at 1:250 scale were carried out in a wind tunnel. Comparisons are made between operation in uniform flow and in the wake of a similarly loaded rotor approximately 6.5 diameters upstream. The measurements were used to validate the output from the VLM simulations, assuming a completely rigid rotor. The trends in the simulation thrust predictions are found to compare well with the uniform flow case, except at low tip speed ratios where there are losses due to stall which are yet to be included in the model. The simple wake model predicts the mean deficit, whilst the periodic boundary condition captures more of the frequency content of the loading in an upstream wake. However, all the thrust loads are over-predicted. The simulation results severely overestimate the bending moment, which needs addressing. However, the reduction in bending due to the simple wake model is found to reflect the experimental data reasonably well.

Experimental and Numerical Investigation of Radial Forces Acting on Centrifugal Pump Impeller

Abstract The paper presents the results of measurements and predictions of radial thrust in centrifugal pump with specific speed ns = 26. In the pump tested, a volute with rectangular cross-section was used. The tests were carried out for several rotational speeds, including speeds above and below the nominal one. Commercial code ANSYS Fluent was used for the calculations. Apart from the predictions of the radial force, the calculations of axial thrust were also conducted, and correlation between thrust and the radial force was found. In the range of the measured rotational speeds, similarity of radial forces was checked.

Mechanistic approach for prediction of forces in micro-drilling of plain and glass-reinforced epoxy sheets

Aerospace and automobile industries extensively use components made of plastics and fiber-reinforced plastics which require micro-machining operations including micro-drilling to be carried out. Various attempts are reported in the literature to study different strategies and model the forces in micro-drilling with a view to produce micro-holes having large aspect ratio and to reduce drill breakage. The force models are more statistical than mechanistic in approach. In the present work, an attempt is made to develop mechanistic models of thrust and torque in micro-drilling of plain epoxy sheets. Material model capturing strain rate and temperature-dependent yield strength of epoxy material and basic principles of machining are employed for this purpose. The mechanistic model for prediction of thrust and torque is validated using well-planned full factorial design of experiments. Experiments are carried out using a carbide drill of 0.5-mm diameter with three levels for speed and feed on a high-speed miniature machine tool specially developed at the laboratory. The material model is extended to glass-reinforced plastics (GRP), and drilling forces are predicted using the proposed mechanistic model. In both cases of plain and GRP sheets, the model predictions are close to the experimentally measured drilling forces.

Numerical Study of Helicopter Rotors in a Ship Airwake

Operating helicopters in a naval environment is challenging because it imposes a pilot workload significantly higher than that during land-based operations. The aerodynamic interaction between the aircraft and the ship wake is known to play an important role in increasing the pilot workload, hence reducing the aircraft capability as a result of maintaining safety. As a further step toward numerical prediction of ship/helicopter operational limitations, computational-fluid-dynamics simulations are conducted for the Canadian Patrol Frigate. The effect of the rotor is included in the simulation, first using an actuator-disc method together with steady calculations, then using rotor blades and the unsteady Reynolds-averaged Navier–Stokes equations. Results using the actuator-disc method demonstrate the importance of coupling effects on the wake and rotor inflow when the rotor is operating close to the ship and therefore the invalidity of superposition methods. The case of a Sea King helicopter main rotor hovering above the deck just before touchdown is reproduced to overcome the limitations of steady calculations and the actuator-disc method. Predictions of rotor thrust compare well with the experimental data available and give confidence in the results. The findings highlight the differences in rotor loading between forward flight and near-deck operation. The possibility of using such simulations for determining safe flight envelopes is discussed as part of the future work.

Comparison of aerodynamic models for Vertical Axis Wind Turbines

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple streamtube model, a double-multiple streamtube model, the actuator cylinder model, a 2D potential flow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models, which explicitly model the wake as a system of vorticity, show mostly differences due to the instantaneous or time averaged formulation of the loading and flow, for which further research is needed.

Semiempirical Thrust Model of Dielectric Barrier Plasma Actuator for Flow Control

AbstractAsymmetric dielectric barrier discharge plasma generating a wall-bounded jet without mechanical moving parts was studied as a flow control device. A reliable model providing thrust value of the plasma actuator is difficult to develop without incurring a heavy calculation cost attributable to its unsteady characteristic and asymmetric electric field distribution. In this paper, a new semiempirical thrust prediction model was developed based on the one-dimensional electrohydrodynamic effect. It is implemented in a computational fluid dynamics solver as a body force term. We determined that the thrust of the plasma actuator is proportional to the energy consumed in the actuator, which is regarded as a capacitor in the alternating current (AC) circuit. An analytic estimation of the capacitance of the actuator is performed, and the sensitive design parameters dielectric constant, thickness and the upper electrode thickness are considered in the capacitance value. The thrust value from the model is inse...

Inverse Analysis and Modeling for Tunneling Thrust on Shield Machine

With the rapid development of sensor and detection technologies, measured data analysis plays an increasingly important role in the design and control of heavy engineering equipment. The paper proposed a method for inverse analysis and modeling based on mass on-site measured data, in which dimensional analysis and data mining techniques were combined. The method was applied to the modeling of the tunneling thrust on shield machines and an explicit expression for thrust prediction was established. Combined with on-site data from a tunneling project in China, the inverse identification of model coefficients was carried out using the multiple regression method. The model residual was analyzed by statistical methods. By comparing the on-site data and the model predicted results in the other two projects with different tunneling conditions, the feasibility of the model was discussed. The work may provide a scientific basis for the rational design and control of shield tunneling machines and also a new way for mass on-site data analysis of complex engineering systems with nonlinear, multivariable, time-varying characteristics.

Computational and Experimental Simulations of the Flow Characteristics of an Aerospike Nozzle

Single Stage To Orbit (SSTO) missions which require its engines to be operated at varying back pressure conditions, use engines operate at high combustion chamber pressures (more than 100bar) with moderate area ratios (AR 70~80). This ensures that the exhaust jet flows full during most part of the operational regimes by optimal expansion at each altitude. Aero-spike nozzle is a kind of altitude adaptation nozzle where requirement of high combustion chamber pressures can be avoided as the flow is adapted to the outside conditions by the virtue of the nozzle configuration. However, the thrust prediction using the conventional thrust equations remains to be a challenge as the nozzle plume shapes vary with the back pressure conditions. In the present work, the performance evaluation of a new aero-spike nozzle is being carried out. Computational studies are carried out to predict the thrust generated by the aero-spike nozzle in varying back pressure conditions which requires the unsteady pressure boundary conditions in the computational domain. Schlieren pictures are taken to validate the computational results. It is found that the flow in the aero-spike nozzle is mainly affected by the base wall pressure variation. The aerospike nozzle exhibits maximum performance in the properly expanded flow regime due to the open wake formation.

Boundary-element method for the prediction of performance of flapping foils with leading-edge separation

AbstractA numerical model based on a boundary-element method is developed to predict the performance of flapping foils for the general cases where vorticities are shed near the leading edge as well as from the trailing edge. The shed vorticities are modelled as desingularized thin shear layers which propagate with the local flow velocity. Special treatments are developed to model the unsteady and alternating leading-edge separation (LES), which is a main element of difficulty for theoretical and numerical analyses of general flapping foils. The present method is compared with existing experiments where it is shown that the inclusion of LES significantly improves the prediction of thrust and efficiency, obtaining excellent agreement with measurements over a broad range of flapping frequencies (Strouhal number) and motion amplitudes (maximum angle of attack). It is found that the neglect of LES leads to substantial over-prediction of the thrust (and efficiency). The effects of LES on thrust generation in terms of the circulation around the foil, the steady and unsteady thrust components, and the vortex-induced pressure on the foil are elucidated. The efficiency and robustness of the method render it suitable for design optimization which generally requires large numbers of performance evaluations. To illustrate this, we present a sample problem of designing the flapping motion, with the inclusion of higher harmonic components, to maximize the efficiency under specified thrust. When optimal higher harmonic motions are included, the performance of the flapping foil is appreciably improved, mitigating the adverse effects of LES vortex on the performance.

A HOLISTIC APPROACH TO UNCERTAINTY QUANTIFICATION WITH APPLICATION TO SUPERSONIC NOZZLE THRUST

In modeling and simulation (MS i.e., a p-box. Implications of sampling over interval versus probabilistic uncertainties in the outer loop are discussed and examples are given showing the effects of the choice of uncertainty propagation and characterization methods. In addition to the uncertainties in model inputs, uncertainties also arise due to modeling deficiencies and numerical approximations. Modeling uncertainties can be reduced by performing additional experiments and numerical uncertainties can be reduced by using additional computational resources; thus, both sources of uncertainty can be modeled as epistemic and can be characterized as intervals and included in the total predictive uncertainty by appropriately broadening the prediction p-box. A simple example is given for the M&S predictions of supersonic nozzle thrust that incorporates and quantifies all three sources of uncertainty.

Open-Water Thrust and Torque Predictions of a Ducted Propeller System with a Panel Method

This paper discusses several modelling aspects that are important for the performance predictions of a ducted propulsor with a low-order Panel Method. The aspects discussed are the alignment of the wake geometry, the influence of the duct boundary layer on the wake pitch, and the influence of a transpiration velocity through the gap. The analysis is carried out for propeller Ka4-70 operating without and inside a modified duct 19A, in which the rounded trailing edge is replaced by a sharp trailing edge. Experimental data for the thrust and torque are used to validate the numerical results. The pitch of the tip vortex is found to have a strong influence on the propeller and duct loads. A good agreement with the measurements is achieved when the wake alignment is corrected for the presence of the duct boundary layer.

Effect of steady and transient wind shear on the wake structure and performance of a horizontal axis wind turbine rotor

ABSTRACTThis paper presents an investigation of the effect of steady and transient free‐stream wind shear on the wake structure and performance characteristics of a horizontal axis wind turbine rotor. A new three‐dimensional unsteady vortex‐panel method potential flow solver based on a free‐vortex wake methodology, AeroSIM+, is used for this purpose. The code is validated using the experimental data from the National Renewable Energy Laboratory Unsteady Aerodynamics Experiments. The effects of vortex core model, core size, expansion, and filament stretching on torque and thrust predictions are investigated. Three‐different wind shear cases, i.e., uniform inflow (no wind shear), steady vertical wind shear that uses a power law velocity profile (Normal Wind Profile, NWP) and transient Extreme Wind Shear (EWS), are investigated. The results show that the existence of wind shear can create a very complex wake structure with substantial asymmetries, streamwise vorticity generation, and non‐periodicities downstream of the turbine rotor. In addition, the blades are subjected to asymmetrical surface pressure variations that in turn result in high amplitude fluctuations in power and thrust levels generated by the turbine. Copyright © 2011 John Wiley & Sons, Ltd.

Prediction of thrust and torque requirements of TBMs with fuzzy logic models

For successful tunnel excavations, selection of proper tunnel boring machine (TBM), optimization of design parameters and prediction of their performance are critical. Normal and rolling forces of disc cutters are used for determination of thrust, torque and power requirement of TBMs as well as prediction of their performance. Much research has been conducted to predict these parameters of disc cutters using analytical, empirical and numerical approaches. In recent years alternative methods, such as fuzzy logic, have been extensively used to deal with subjects having ambiguities and uncertainties. A model was established to predict normal forces of constant cross section (CCS) disc cutters in the rock cutting process by using fuzzy logic method. The other model which predicts specific energy requirement of disc cutter can also be used for predicting the rolling forces of these cutters. These models are based on experience and verified the database which consists of linear cutting test results generated at the Earth Mechanics Institute of the Colorado School of Mines. The models predict forces of disc cutters using uniaxial compressive and tensile strength of rocks, disc diameter and tip width, penetration and spacing of cuts.

Semiempirical model of a wheel-soil system

Developing new concepts for the prediction of off-road traction is becoming essential as an increasing number of sport utility vehicles (SUVs), sport activity vehicles (SAVs), and other off-road vehicles arrive on the market. The prediction of off-road traction is a difficult problem because of the number of factors affecting wheel performance on soft soils or snow. Most of the existing methods for wheel-soil thrust prediction are based on Coulomb’s equation, in which stresses acting on the wheel-soil contact patch are analyzed. The objective of this work was to develop a new method to infer mathematical models of a wheel-soil system in which soil-stress states are correlated with the forces acting on a road wheel. A set of model equations is obtained by means of the system identification method with the use of experimental data gathered in the field with real vehicles. This paper includes a description of the experimental setup, procedures, and methods used in the tests. The experimental method is based on simultaneous measurements of the soil-stress state and wheel forces during test runs of an instrumented vehicle over soft soil surfaces. Soil-stress states consist of three principal stresses and their direction cosines, which are determined with the use of a stress state transducer (SST) placed at a depth of 15–30 cm under the wheels. Longitudinal, vertical, and transverse wheel forces are measured with a six-element wheel force transducer. The wheel forces obtained in the test runs are correlated with the respective soil stresses. Based on the data, three families of models were obtained by means of the system identification method.

Influence Research of Velocity on Lubricating Properties of Sector Cavity Multi-Pad Hydrostatic Thrust Bearing

Lubricating characteristics of sector cavity multi-pad hydrostatic thrust bearing are affected significantly by velocity, poor design can cause lubricant film rupture and dry friction, even leading to failure of hydrostatic bearing tribology. For this problem, the Computational Fluid Dynamics and the lubrication theory have been used to analyze velocity characteristics of the parameters such as cavity pressure of oil, oil cavity flow and film thickness, to gain relationship between velocity and lubricating properties of sector cavity multi-pad hydrostatic thrust bearing, avoiding the occurrence of hydrostatic bearing tribological failure. It is shown that along with the speed of the worktable increasing, the flow of lubricant oil caused by inertia and centrifugal force become larger, the flow of efflux from the oil cavity also become larger, causing the pressure drop of the oil cavity, the thinning of the film thickness, the occurrence of film rupture and dry friction and failure of hydrostatic bearing tribology. The study provides the basic data for the hydrostatic thrust bearing design, the lubrication and the experiment, implements of the prediction of the hydrostatic thrust bearing lubrication velocity characteristics, and reaches the purpose of reducing economic loss.

Assessment of Bhatnagar-Gross-Krook Approaches for Near Continuum Regime Nozzle Flows

Accurate and numerically efficient modeling of low-to-moderate Reynolds number nozzle flow expansions to vacuum can be difficult due to the presence of multiple flow length scales. Such simulations are important for the prediction of propulsive thrust as well as spacecraft contamination, both of which can be difficult to measure in ground-based facilities. To that end, conical nozzle flows were studied for Reynolds numbers of 1230 and 12,300 using the direct simulation Monte Carlo method, Navier―Stokes with velocity slip and temperature jump boundary conditions, and statistical and deterministic approaches to the solution of the Bhatnagar―Gross―Krook and ellipsoidal-statistical Bhatnagar―Gross―Krook equations. The deterministic and statistical solutions of the Bhatnagar―Gross―Krook equation were found to be in good agreement with the benchmark direct simulation Monte Carlo results. Statistical Bhatnagar―Gross―Krook and ellipsoidal-statistical Bhatnagar―Gross―Krook methods were also found to be more efficient methods than direct simulation Monte Carlo in the continuum and near-continuum regime, and more accurate than the Navier―Stokes equations in the portions of the flow with rarefaction, such as the boundary layer and the flow around the nozzle lip.

Development and Validation of a CFD Technique for the Aerodynamic Analysis of HAWT

This paper demonstrates the potential of a compressible Navier–Stokes CFD method for the analysis of horizontal axis wind turbines. The method was first validated against experimental data of the NREL/NASA-Ames Phase VI (Hand, et al., 2001, “Unsteady Aerodynamics Experiment Phase, VI: Wind Tunnel Test Configurations and Available Data Campaigns,” NREL, Technical Report No. TP-500-29955) wind-tunnel campaign at 7 m/s, 10 m/s, and 20 m/s freestreams for a nonyawed isolated rotor. Comparisons are shown for the surface pressure distributions at several stations along the blades as well as for the integrated thrust and torque values. In addition, a comparison between measurements and CFD results is shown for the local flow angle at several stations ahead of the wind turbine blades. For attached and moderately stalled flow conditions the thrust and torque predictions are fair, though improvements in the stalled flow regime are necessary to avoid overprediction of torque. Subsequently, the wind-tunnel wall effects on the blade aerodynamics, as well as the blade/tower interaction, were investigated. The selected case corresponded to 7 m/s up-wind wind turbine at 0 deg of yaw angle and a rotational speed of 72 rpm. The obtained results suggest that the present method can cope well with the flows encountered around wind turbines providing useful results for their aerodynamic performance and revealing flow details near and off the blades and tower.

Numerical simulation of flow over an airfoil with a cross flow fan as a lift generating member in a new aircraft model

PurposeThe purpose of this paper is to show how flow over the airfoil comprising a cross flow fan has been solved by developing a computational fluid dynamics (CFD) code. This research was going to find aerodynamic coefficients and static pressure distribution over the airfoil surfaces. The eccentric vortex motion observed earlier by other researchers in cross flow fan has been studied by numerical method. Also, the airfoil trailing vortex size variation by free stream and fan rotational speed has been surveyed.Design/methodology/approachFlow over the airfoil has been investigated by CFD. At the airfoil solid walls no slip condition (zero velocity) was applied. Re‐normalization group k‐ε model was used for turbulence modeling. The pressure‐velocity coupling was calculated by the SIMPLEC algorithm. Second‐order upwind discretization was considered for the convection terms. Finite volume method with rectangular computational cells was used for whole the solution domain.FindingsCFD predicted lift force was in good agreement with experimental data with the error of 8.26 percent, while the error of thrust prediction was 14.17 percent. Both errors are generally acceptable for an engineering application. Some key flow features observed previously by experiments has also been reproduced by simulation, notably motion of the eccentric and trailing vortices. At low‐fan rotational speed, the eccentric vortex formed below the shaft of the fan but at high‐rotational speed, eccentric vortex came up and moved toward the airfoil leading edge. It was shown that increasing free stream velocity or decreasing fan rotational speed leads to a larger trailing vortex and vice versa. It was showed that the airfoil lift and thrust are highly depended on the fan rotational speed. These forces will increase by enhancing the fan rotational speed.Research limitations/implicationsBecause of complicated geometry of the airfoil, 2D analysis of the flow over the airfoil has been carried out. This simplification leads to higher discrepancies between experimental data and numerical solution.Practical implicationsThis paper provides a detailed study of the Fanwing airfoil. This airfoil is very new and researches in this area are very limited. So, this paper can be helpful for other researches involved in this topic as well as aerospace industries.Originality/valueThis paper is valuable for researchers in the new and up‐to‐date concept of the airfoil comprising a cross flow fan (Fanwing airfoil). This work is original.

상사법칙을 이용한 수직발사 유도탄 추력곡선예측

본 논문은 검증된 수직발사 유도탄을 모델로 고려하여 개발하려는 수직발사 유도탄의 추력을 예측하는 방법을 제안한다. 개발하려는 수직발사 유도탄의 추력을 예측하기위해 모델에 상사법칙과 Pi 이론을 적용하였다. 검증된 수직발사 유도탄의 6-DOF 프로그램에 기반한 예측 결과와 개발하려는 수직발사 유도탄의 모의시험 결과를 비교하여 제안된 방법의 타당성을 검증하였다. In this paper, a thrust prediction method for a developing vertical launching missile is proposed through considering a verified vertical launching missile(a baseline missile) as a model. In order to predict thrust profile of a developing vertical launching missile, both Similarity law and Pi theory are applied to the model. By comparing prediction results based on the 6-DOF program of a baseline missile with simulation results of a developing vertical launching missile, the proposed method has been indirectly verified.