MSE3 Ch10 Dynamics
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CHAPTER 20 Wind Turbine Noise Measurements and Abatement
CHAPTER 20 Wind turbine noise measurements and abatement methods Panagiota Pantazopoulou BRE, Watford, UK. This chapter presents an overview of the types, the measurements and the potential acoustic solutions for the noise emitted from wind turbines. It describes the fre- quency and the acoustic signature of the sound waves generated by the rotating blades and explains how they propagate in the atmosphere. In addition, the avail- able noise measurement techniques are being presented with special focus on the technical challenges that may occur in the measurement process. Finally, a discus- sion on the noise treatment methods from wind turbines referring to a range of the existing abatement methods is being presented. 1 Introduction Wind turbines generate two types of noise: aerodynamic and mechanical. A tur- bine’s sound power is the combined power of both. Aerodynamic noise is gener- ated by the blades passing through the air. The power of aerodynamic noise is related to the ratio of the blade tip speed to wind speed. The mechanical noise is associated with the relevant motion between the various parts inside the nacelle. The compartments move or rotate in order to convert kinetic energy to electricity with the expense of generating sound waves and vibration which is transmitted through the structural parts of the turbine. Depending on the turbine model and the wind speed, the aerodynamic noise may seem like buzzing, whooshing, pulsing, and even sizzling. Downwind tur- bines with their blades downwind of the tower cause impulsive noise which can travel far and become very annoying for people. The low frequency noise gener- ated from a wind turbine is primarily the result of the interaction of the aerody- namic lift on the blades and the atmospheric turbulence in the wind. -
Atmospheric Effects on Traffic Noise Propagation
TRANSPORTATION RESEARCH RECORD 1255 59 Atmospheric Effects on Traffic Noise Propagation ROGER L. WAYSON AND WILLIAM BOWLBY Atmospheric effects on traffic noise propagation have largely L 0 sound level at a reference distance, been ignored during measurements and modeling, even though Ageo attenuation due to geometric spreading, it has generally been accepted that the effects may produce large Ab insertion loss due to diffraction, changes in receiver noise levels. Measurement of traffic noise at L, level increases due to reflection, and multiple locations concurrently with measurement of meteoro Ac attenuation due to ground characteristics and envi logical data is described. Statistical methods were used to evaluate the data. Atmospheric effects on traffic noise levels were shown ronmental effects. to be significant, even at very short distances; parallel components It should be noted that all levels in dB in this paper are of the wind (which are usually ignored) were important at second 2 row receivers; turbulent scattering increased noise levels near the referenced to 2 x 10-s N/m • ground more than refractive ray bending for short-distance prop The last term on the right side of Equation 1, A,, consists agation; and temperature lapse rates were not as important as of three parameters: ground attenuation, attenuation due to wind shear very near the highway. A statistical model was devel atmospheric absorption, and attenuation due to atmospheric oped to predict excess attenuations due to atmospheric effects. refraction. (2) Outdoor noise propagation has been studied since the time of the Greek philosopher Chrysippus (240 B. C.). Modern where prediction models have become accurate, and the advent of computers has increased the capabilities of models. -
Balanced Flow Natural Coordinates
Balanced Flow • The pressure and velocity distributions in atmospheric systems are related by relatively simple, approximate force balances. • We can gain a qualitative understanding by considering steady-state conditions, in which the fluid flow does not vary with time, and by assuming there are no vertical motions. • To explore these balanced flow conditions, it is useful to define a new coordinate system, known as natural coordinates. Natural Coordinates • Natural coordinates are defined by a set of mutually orthogonal unit vectors whose orientation depends on the direction of the flow. Unit vector tˆ points along the direction of the flow. ˆ k kˆ Unit vector nˆ is perpendicular to ˆ t the flow, with positive to the left. kˆ nˆ ˆ t nˆ Unit vector k ˆ points upward. ˆ ˆ t nˆ tˆ k nˆ ˆ r k kˆ Horizontal velocity: V = Vtˆ tˆ kˆ nˆ ˆ V is the horizontal speed, t nˆ ˆ which is a nonnegative tˆ tˆ k nˆ scalar defined by V ≡ ds dt , nˆ where s ( x , y , t ) is the curve followed by a fluid parcel moving in the horizontal plane. To determine acceleration following the fluid motion, r dV d = ()Vˆt dt dt r dV dV dˆt = ˆt +V dt dt dt δt δs δtˆ δψ = = = δtˆ t+δt R tˆ δψ δψ R radius of curvature (positive in = R δs positive n direction) t n R > 0 if air parcels turn toward left R < 0 if air parcels turn toward right ˆ dtˆ nˆ k kˆ = (taking limit as δs → 0) tˆ R < 0 ds R kˆ nˆ ˆ ˆ ˆ t nˆ dt dt ds nˆ ˆ ˆ = = V t nˆ tˆ k dt ds dt R R > 0 nˆ r dV dV dˆt = ˆt +V dt dt dt r 2 dV dV V vector form of acceleration following = ˆt + nˆ dt dt R fluid motion in natural coordinates r − fkˆ ×V = − fVnˆ Coriolis (always acts normal to flow) ⎛ˆ ∂Φ ∂Φ ⎞ − ∇ pΦ = −⎜t + nˆ ⎟ pressure gradient ⎝ ∂s ∂n ⎠ dV ∂Φ = − dt ∂s component equations of horizontal V 2 ∂Φ momentum equation (isobaric) in + fV = − natural coordinate system R ∂n dV ∂Φ = − Balance of forces parallel to flow. -
Industrial Aerodynamics
INDUSTRIAL AERODYNAMICS Unit I Wind Energy Collectors INTRODUCTION Air Movement Wind Air Current Circulation The horizontal movement of air along the earth’s surface is called a Wind. The vertical movement of the air is known as an air current. Winds and air current together comprise a system of circulation in the atmosphere. TYPES OF WINDS On the earth’s surface, certain winds blow constantly in a particular direction throughout the year. These are known as the ‘Prevailing Winds’. They are also called the Permanent or the Planetary Winds. Certain winds blow in one direction in one season and in the opposite direction in another. They are known as Periodic Winds. Then, there are Local Winds in different parts of the world. 1. Planetary Winds: There are three main planetary winds that constantly blow in the same direction all around the world. They are also called prevailing or permanent winds. 1.Trade Winds: Blow from the subtropical high pressure belt towards the Equator. They are called the north-east trades in the northern hemisphere and south-east trades in the southern hemisphere. 2.Westerly winds: Blow from the same subtropical high pressure belts, towards 60˚ S and 60˚ N latitude. They are called the sought Westerly wind sin the northern hemisphere and North Westerly winds in the southern hemispheres. 3.Polar Winds Blow from the polar high pressure to the sub polar low pressure area. In the northern hemisphere, their direction is from the north-east. In the southern hemisphere, they blow from the south-east. 2. Periodic Winds These winds are known to blow for a certain time in a certain direction - it may be for a part of a day or a particular season of the year. -
A Generalization of the Thermal Wind Equation to Arbitrary Horizontal Flow CAPT
A Generalization of the Thermal Wind Equation to Arbitrary Horizontal Flow CAPT. GEORGE E. FORSYTHE, A.C. Hq., AAF Weather Service, Asheville, N. C. INTRODUCTION N THE COURSE of his European upper-air analysis for the Army Air Forces, Major R. C. I Bundgaard found that the shear of the observed wind field was frequently not parallel to the isotherms, even when allowance was made for errors in measuring the wind and temperature. Deviations of as much as 30 degrees were occasionally found. Since the ther- mal wind relation was found to be very useful on the occasions where it did give the direction and spacing of the isotherms, an attempt was made to give qualitative rules for correcting the observed wind-shear vector, to make it agree more closely with the shear of the geostrophic wind (and hence to make it lie along the isotherms). These rules were only partially correct and could not be made quantitative; no general rules were available. Bellamy, in a recent paper,1 has presented a thermal wind formula for the gradient wind, using for thermodynamic parameters pressure altitude and specific virtual temperature anom- aly. Bellamy's discussion is inadequate, however, in that it fails to demonstrate or account for the difference in direction between the shear of the geostrophic wind and the shear of the gradient wind. The purpose of the present note is to derive a formula for the shear of the actual wind, assuming horizontal flow of the air in the absence of frictional forces, and to show how the direction and spacing of the virtual-temperature isotherms can be obtained from this shear. -
Small Lightweight Aircraft Navigation in the Presence of Wind Cornel-Alexandru Brezoescu
Small lightweight aircraft navigation in the presence of wind Cornel-Alexandru Brezoescu To cite this version: Cornel-Alexandru Brezoescu. Small lightweight aircraft navigation in the presence of wind. Other. Université de Technologie de Compiègne, 2013. English. NNT : 2013COMP2105. tel-01060415 HAL Id: tel-01060415 https://tel.archives-ouvertes.fr/tel-01060415 Submitted on 3 Sep 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Par Cornel-Alexandru BREZOESCU Navigation d’un avion miniature de surveillance aérienne en présence de vent Thèse présentée pour l’obtention du grade de Docteur de l’UTC Soutenue le 28 octobre 2013 Spécialité : Laboratoire HEUDIASYC D2105 Navigation d'un avion miniature de surveillance a´erienneen pr´esencede vent Student: BREZOESCU Cornel Alexandru PHD advisors : LOZANO Rogelio CASTILLO Pedro i ii Contents 1 Introduction 1 1.1 Motivation and objectives . .1 1.2 Challenges . .2 1.3 Approach . .3 1.4 Thesis outline . .4 2 Modeling for control 5 2.1 Basic principles of flight . .5 2.1.1 The forces of flight . .6 2.1.2 Parts of an airplane . .7 2.1.3 Misleading lift theories . 10 2.1.4 Lift generated by airflow deflection . -
ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere. -
Chapter 7 Balanced Flow
Chapter 7 Balanced flow In Chapter 6 we derived the equations that govern the evolution of the at- mosphere and ocean, setting our discussion on a sound theoretical footing. However, these equations describe myriad phenomena, many of which are not central to our discussion of the large-scale circulation of the atmosphere and ocean. In this chapter, therefore, we focus on a subset of possible motions known as ‘balanced flows’ which are relevant to the general circulation. We have already seen that large-scale flow in the atmosphere and ocean is hydrostatically balanced in the vertical in the sense that gravitational and pressure gradient forces balance one another, rather than inducing accelera- tions. It turns out that the atmosphere and ocean are also close to balance in the horizontal, in the sense that Coriolis forces are balanced by horizon- tal pressure gradients in what is known as ‘geostrophic motion’ – from the Greek: ‘geo’ for ‘earth’, ‘strophe’ for ‘turning’. In this Chapter we describe how the rather peculiar and counter-intuitive properties of the geostrophic motion of a homogeneous fluid are encapsulated in the ‘Taylor-Proudman theorem’ which expresses in mathematical form the ‘stiffness’ imparted to a fluid by rotation. This stiffness property will be repeatedly applied in later chapters to come to some understanding of the large-scale circulation of the atmosphere and ocean. We go on to discuss how the Taylor-Proudman theo- rem is modified in a fluid in which the density is not homogeneous but varies from place to place, deriving the ‘thermal wind equation’. Finally we dis- cuss so-called ‘ageostrophic flow’ motion, which is not in geostrophic balance but is modified by friction in regions where the atmosphere and ocean rubs against solid boundaries or at the atmosphere-ocean interface. -
ATM 316 - the “Thermal Wind” Fall, 2016 – Fovell
ATM 316 - The \thermal wind" Fall, 2016 { Fovell Recap and isobaric coordinates We have seen that for the synoptic time and space scales, the three leading terms in the horizontal equations of motion are du 1 @p − fv = − (1) dt ρ @x dv 1 @p + fu = − ; (2) dt ρ @y where f = 2Ω sin φ. The two largest terms are the Coriolis and pressure gradient forces (PGF) which combined represent geostrophic balance. We can define geostrophic winds ug and vg that exactly satisfy geostrophic balance, as 1 @p −fv ≡ − (3) g ρ @x 1 @p fu ≡ − ; (4) g ρ @y and thus we can also write du = f(v − v ) (5) dt g dv = −f(u − u ): (6) dt g In other words, on the synoptic scale, accelerations result from departures from geostrophic balance. z R p z Q δ δx p+δp x Figure 1: Isobaric coordinates. It is convenient to shift into an isobaric coordinate system, replacing height z by pressure p. Remember that pressure gradients on constant height surfaces are height gradients on constant pressure surfaces (such as the 500 mb chart). In Fig. 1, the points Q and R reside on the same isobar p. Ignoring the y direction for simplicity, then p = p(x; z) and the chain rule says @p @p δp = δx + δz: @x @z 1 Here, since the points reside on the same isobar, δp = 0. Therefore, we can rearrange the remainder to find δz @p = − @x : δx @p @z Using the hydrostatic equation on the denominator of the RHS, and cleaning up the notation, we find 1 @p @z − = −g : (7) ρ @x @x In other words, we have related the PGF (per unit mass) on constant height surfaces to a \height gradient force" (again per unit mass) on constant pressure surfaces. -
Wind Power Meteorology. Part I: Climate and Turbulence 3
WIND ENERGY Wind Energ., 1, 2±22 (1998) Review Wind Power Meteorology. Article Part I: Climate and Turbulence Erik L. Petersen,* Niels G. Mortensen, Lars Landberg, Jùrgen Hùjstrup and Helmut P. Frank, Department of Wind Energy and Atmospheric Physics, Risù National Laboratory, Frederiks- borgvej 399, DK-4000 Roskilde, Denmark Key words: Wind power meteorology has evolved as an applied science ®rmly founded on boundary wind atlas; layer meteorology but with strong links to climatology and geography. It concerns itself resource with three main areas: siting of wind turbines, regional wind resource assessment and assessment; siting; short-term prediction of the wind resource. The history, status and perspectives of wind wind climatology; power meteorology are presented, with emphasis on physical considerations and on its wind power practical application. Following a global view of the wind resource, the elements of meterology; boundary layer meteorology which are most important for wind energy are reviewed: wind pro®les; wind pro®les and shear, turbulence and gust, and extreme winds. *c 1998 John Wiley & turbulence; extreme winds; Sons, Ltd. rotor wakes Preface The kind invitation by John Wiley & Sons to write an overview article on wind power meteorology prompted us to lay down the fundamental principles as well as attempting to reveal the state of the artÐ and also to disclose what we think are the most important issues to stake future research eorts on. Unfortunately, such an eort calls for a lengthy historical, philosophical, physical, mathematical and statistical elucidation, resulting in an exorbitant requirement for writing space. By kind permission of the publisher we are able to present our eort in full, but in two partsÐPart I: Climate and Turbulence and Part II: Siting and Models. -
In Wind and Ocean Currents
PAPERS IN PHYSICAL OCEANOGRAPHY AND METEOROLOGY PUBLISHED BY MASSACHUSETTS INSTITUTE OF TECHNOLOGY AND WOODS HOLE OCEANOGRAPHIC INSTITUTION (In continuation of Massachusetts Institute of Technology Meteorological Papers) VOL. III, NO.3 THE LAYER OF FRICTIONAL INFLUENCE IN WIND AND OCEAN CURRENTS BY c.-G. ROSSBY AND R. B. MONTGOMERY Contribution No. 71 from the Woods Hole Oceanographic Institution .~ J~\ CAMBRIDGE, MASSACHUSETTS Ap~il, 1935 CONTENTS i. INTRODUCTION 3 II. ADIABATIC ATMOSPHERE. 4 1. Completion of Solution for Adiabatic Atmosphere 4 2. Light Winds and Residual Turbulence 22 3. A Study of the Homogeneous Layer at Boston 25 4. Second Approximation 4° III. INFLUENCE OF STABILITY 44 I. Review 44 2. Stability in the Boundary Layer 47 3. Stability within Entire Frictional Layer 56 IV. ApPLICATION TO DRIFT CURRENTS. 64 I. General Commen ts . 64 2. The Homogeneous Layer 66 3. Analysis of Material 67 4. Results of Analysis . 69 5. Scattering of the Observations and Advection 72 6. Oceanograph Observations 73 7. Wind Drift of the Ice 75 V. LENGTHRELATION BETWEEN THE VELOCITY PROFILE AND THE VALUE OF THE85 MIXING ApPENDIX2.1. StirringTheoretical in Shallow Comments . Water 92. 8885 REFERENCESSUMMARYModified Computation of the Boundary Layer in Drift Currents 9899 92 1. INTRODUCTION The purpose of the present paper is to analyze, in a reasonably comprehensive fash- ion, the principal factors controlling the mean state of turbulence and hence the mean velocity distribution in wind and ocean currents near the surface. The plan of the in- vestigation is theoretical but efforts have been made to check each major step or result through an analysis of available measurements. -
UNIVERSITY of CALIFORNIA SAN DIEGO Mesoscale Dynamics Of
UNIVERSITY OF CALIFORNIA SAN DIEGO Mesoscale Dynamics of Atmospheric Rivers A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Oceanography by Reuben Demirdjian Committee in charge: F. Martin Ralph, Chair Joel Norris, Co-Chair Amato Evan Jan Kleissl Richard Rotunno Shang-Ping Xie 2020 Copyright Reuben Demirdjian, 2020 All rights reserved. The Dissertation of Reuben Demirdjian is approved, and it is acceptable in quality and form for publication on microfilm and electronically: _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ Co-chair _____________________________________________________________ Chair University of California San Diego 2020 iii DEDICATION For my family (friends included) iv EPIGRAPH “Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every