Sparse identification of nonlinear unsteady aerodynamics of the oscillating airfoil

Reduced-order models are widely used in aerospace engineering. A model for unsteady aerodynamics is desirable for designing the blades of wind turbines. Recently, sparse identification of nonlinear dynamics with control was introduced to identify the parameters of an input-output dynamical system. In this paper, two models for attached flows and one for separated flows are identified through this technique. For the unsteady lift of the attached flow, Model I is a linear model that presents the dynamic change of an unsteady lift to a static lift. Model II was built based on Model I in order to obtain a more general system with closed-loop control. It has a first-order inert element that delays the overall input of the static lift. The Model II results replicate the training data very well and give an accurate prediction of other oscillating cases with different oscillation amplitudes, reduced frequency or mean angle of attack. For the unsteady lift of the separated flow, Model III is identified as a nonlinear model, which also has a first-order inert element. This model captures the nonlinear aerodynamics of the separated flow and replicates the training cases well. In addition, the prediction of Model III has good agreement with the numerical results.

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A theoretical investigation of enhanced lift in the presence of thin aerofoil stall

The Aeronautical Journal ◽

10.1017/s0001924000027901 ◽

1999 ◽

Vol 103 (1023) ◽

pp. 237-244 ◽

Cited By ~ 2

Author(s):

W. W. H. Yeung ◽

G. V. Parkinson

Keyword(s):

Flat Plate ◽

Flow Model ◽

Separated Flow ◽

Leading Edge ◽

Geometrical Parameters ◽

Separation Flow ◽

Attached Flow ◽

Positive Angle ◽

Edge Separation ◽

Potential Flow Model

Abstract A theoretical study is presented for the investigation of a potential-flow model for enhancing lift over a flat-plate aerofoil experiencing thin aerofoil stall. Rather than suppressing the leading-edge separation, flow is assumed to separate tangentially at the leading edge and made to reattach smoothly at the tip of a forward-facing fence joining the plate tangentially on its upper surface to avoid any unnecessary stagnated flow. The length of the fence and its location from the leading edge form two geometrical parameters. At any positive angle of attack, the resulting bounding streamline emanating from the leading edge and terminating at the tip of the fence is simulated by using suitable mathematical singularities subject to boundary conditions such as attaining a finite velocity at each critical point of the conformal mapping involved, and the condition of finite pressure gradient at reattachment, when applicable. Computational results from varying these two geometrical parameters indicate that the lift from each model is enhanced, as compared with the attached flow model around a simple flat plate and the original separated flow model by Kirchhoff.

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Developments in computational methods for high-lift aerodynamics

The Aeronautical Journal ◽

10.1017/s0001924000016262 ◽

1988 ◽

Vol 92 (917) ◽

pp. 265-288 ◽

Cited By ~ 11

Author(s):

D. A. King ◽

B. R. Williams

Keyword(s):

Separated Flow ◽

Direct Methods ◽

Viscous Flows ◽

Inviscid Flow ◽

Contributory Factor ◽

High Lift ◽

First Order ◽

Boundary Layer Equations ◽

Attached Flow ◽

The Uk

SummaryViscous/inviscid interaction techniques for calculating the flow about multiple-element aerofoils have been under development in the UK for the last decade producing such programs as MAVIS and HILDA. These methods give reasonable predictions of the lift for viscous attached flow, but fail to give an estimate of the maximum lift and the associated flow separations on the aerofoils. The methods also fail to give adequate predictions of the drag for both attached and separated flow. The disappointing performance of the methods in predicting maximum lift stems primarily from the use of direct methods to solve the first order boundary-layer equations, whilst the poor drag predictions arise from inadequate methods for predicting the development of the flow over the flap. The assumption of incompressible flow could also be a contributory factor in both cases. Methods of overcoming the first restriction are described by using a more appropriate coupling between the inviscid and viscous flows which properly assigns the correct role to each partner in the coupling: this approach is illustrated by ‘semi-inverse’ and ‘quasi-simultaneous’ couplings of a finite-element method for the compressible inviscid flow with an integral method for the boundary layers and wakes. Some methods for calculating the compressible flow about multiple-element aerofoils are also reviewed. However these improvements do not give an adequate estimate of the drag so possible improvements to the calculation of the flow over the flap are discussed.

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Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽

10.3390/mi12050510 ◽

2021 ◽

Vol 12 (5) ◽

pp. 510

Author(s):

Yan Huang ◽

Bifen Shu ◽

Shengnan Zhou ◽

Qi Shi

Keyword(s):

Pressure Drop ◽

Flow Model ◽

Two Phase Flow ◽

Flow Boiling ◽

Separated Flow ◽

Heat Fluxes ◽

Phase Flow ◽

Vapor Quality ◽

Two Phase ◽

Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

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1.1-µm Band Extended Wide-Bandwidth Wavelength-Swept Laser Based on Polygonal Scanning Wavelength Filter

Sensors ◽

10.3390/s21093053 ◽

2021 ◽

Vol 21 (9) ◽

pp. 3053

Author(s):

Gi Hyen Lee ◽

Soyeon Ahn ◽

Jinhwa Gene ◽

Min Yong Jeon

Keyword(s):

Optical Amplifiers ◽

Dynamic Change ◽

Cholesteric Liquid Crystal ◽

Average Power ◽

Semiconductor Optical Amplifiers ◽

Scanning Speed ◽

Reflection Band ◽

First Order ◽

Wavelength Filter ◽

Buildup Time

We demonstrated a 1.1-µm band extended wideband wavelength-swept laser (WSL) that combined two semiconductor optical amplifiers (SOAs) based on a polygonal scanning wavelength filter. The center wavelengths of the two SOAs were 1020 nm and 1140 nm, respectively. Two SOAs were connected in parallel in the form of a Mach-Zehnder interferometer. At a scanning speed of 1.8 kHz, the 10-dB bandwidth of the spectral output and the average power were approximately 228 nm and 16.88 mW, respectively. Owing to the nonlinear effect of the SOA, a decrease was observed in the bandwidth according to the scanning speed. Moreover, the intensity of the WSL decreased because the oscillation time was smaller than the buildup time. In addition, a cholesteric liquid crystal (CLC) cell was fabricated as an application of WSL, and the dynamic change of the first-order reflection of the CLC cell in the 1-µm band was observed using the WSL. The pitch jumps of the reflection band occurred according to the electric field applied to the CLC cell, and instantaneous changes were observed.

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Prediction of Socio-Economic Indicators for Urban Planning Using VHR Satellite Imagery and Spatial Analysis

Remote Sensing ◽

10.3390/rs12111730 ◽

2020 ◽

Vol 12 (11) ◽

pp. 1730 ◽

Cited By ~ 2

Author(s):

Gebhard Warth ◽

Andreas Braun ◽

Oliver Assmann ◽

Kevin Fleckenstein ◽

Volker Hochschild

Keyword(s):

Spatial Analysis ◽

Urban Planning ◽

Urban Areas ◽

Residential Buildings ◽

Dynamic Change ◽

Training Data ◽

Infrastructure Planning ◽

Economic Point ◽

Steady Growth ◽

Building Typology

Ongoing urbanization leads to steady growth of urban areas. In the case of highly dynamic change of municipalities, due to the rates of change, responsible administrations often are challenged or struggle with capturing present states of urban sites or accurately planning future urban development. An interest for urban planning lies on socio-economic conditions, as consumption and production of disposable goods are related to economic possibilities. Therefore, we developed an approach to generate relevant parameters for infrastructure planning by means of remote sensing and spatial analysis. In this study, the single building defines the spatial unit for the parameters. In the case city Belmopan (Belize), based on WorldView-1 data we manually define a city covering building dataset. Residential buildings are classified to eight building types which are locally adapted to Belmopan. A random forest (RF) classifier is trained with locally collected training data. Through household interviews focusing on household assets, income and educational level, a socio-economic point (SEP) scaling is defined, which correlates very well with the defined building typology. In order to assign socio-economic parameters to the single building, five socio-economic classes (SEC) are established based on SEP statistics for the building types. The RF building type classification resulted in high accuracies. Focusing on the three categories to describe residential socio-economic states allowed high correlations between the defined building and socio-economic points. Based on the SEP we projected a citywide residential socio-economic building classification to support supply and disposal infrastructure planning.

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On the first-order phase transition in a cellular automaton traffic flow model without a slow-to-start effect

Journal of Statistical Mechanics Theory and Experiment ◽

10.1088/1742-5468/2010/03/p03018 ◽

2010 ◽

Vol 2010 (03) ◽

pp. P03018 ◽

Cited By ~ 15

Author(s):

Cheng-Jie Jin ◽

Wei Wang ◽

Rui Jiang ◽

Kun Gao

Keyword(s):

Phase Transition ◽

Cellular Automaton ◽

Traffic Flow ◽

Order Phase Transition ◽

Flow Model ◽

Traffic Flow Model ◽

First Order ◽

First Order Phase Transition ◽

First Order Phase

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An Investigation of Flow Fields Over Multi-Element Aerofoils

Journal of Fluids Engineering ◽

10.1115/1.1431267 ◽

2001 ◽

Vol 124 (1) ◽

pp. 154-165 ◽

Cited By ~ 7

Author(s):

S. R. Maddah ◽

H. H. Bruun

Keyword(s):

Flow Field ◽

Computational Study ◽

Separated Flow ◽

Mean Flow ◽

Model Configuration ◽

Attached Flow ◽

The Mean ◽

Flap Deflection ◽

Comparative Results ◽

Lift And Drag

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.

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ON CONDITIONING FOR A GENERAL SYSTEM OF FOUR POINT BOUNDARY VALUE PROBLEMS

Tamkang Journal of Mathematics ◽

10.5556/j.tkjm.27.1996.4337 ◽

1996 ◽

Vol 27 (3) ◽

pp. 219-225

Author(s):

M. S. N. MURTY

Keyword(s):

Differential Equation ◽

Fundamental Matrix ◽

Close Relationships ◽

General System ◽

Point Boundary ◽

Matrix Differential Equation ◽

Growth Behaviour ◽

First Order ◽

Matrix Differential ◽

The Stability

In this paper we investigate the close relationships between the stability constants and the growth behaviour of the fundamental matrix to the general FPBVP'S associated with the general first order matrix differential equation.

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