Drag Lift Variación II

8/9/2019 Drag Lift Variación II

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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 1

Flow over bodies;Lift and Drag. Ob e!tives

"ave an intuitive understanding of the variousph#si!al pheno$ena su!h as drag% fri!tion andpressure drag% drag redu!tion% and lift.Cal!ulate the drag for!e asso!iated with flow

over !o$$on geo$etries.&nderstand the effe!ts of flow regi$e on thedrag !oeffi!ients asso!iated with flow over!#linders and spheres

&nderstand the funda$entals of flow overairfoils% and !al!ulate the drag and lift for!esa!ting on airfoils.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow '

Motivation


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Motivation


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow (

E)ternal Flow

*odies and vehi!les in $otion% or with flow over the$%e)perien!e fluid+d#na$i! for!es and $o$ents.E)a$ples in!lude: air!raft% auto$obiles% buildings%ships% sub$arines% turbo$a!hines.

,hese proble$s are often !lassified asExternal Flows.

Fuel e!ono$#% speed% a!!eleration% $aneuverabilit#%stabilit#% and !ontrol are dire!tl# related to theaerod#na$i!-h#drod#na$i! for!es and $o$ents.

eneral /DOF $otion of vehi!les is des!ribed b# /e0uations for the linear surge% heave% swa#2 andangular roll% pit!h% #aw2 $o$entu$.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow

Fluid D#na$i! For!es and Mo$ents

4hips in waves present one of the $ostdiffi!ult /DOF proble$s.

5irplane in level stead# flight: drag 6 thrustand lift 6 weight.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow /

Drag and Lift

Fluid d#na$i! for!es aredue to pressure andvis!ous for!es a!ting onthe bod# surfa!e.

Drag: !o$ponentparallel to flow dire!tion.Lift: !o$ponent nor$al

to flow dire!tion.


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Drag and Lift

Lift and drag for!es !an be found b#integrating pressure and wall+shear stress.


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Drag and Lift

9n addition to geo$etr#% lift F L and drag F D for!esare a fun!tion of densit# ρ and velo!it# V .Di$ensional anal#sis gives ' di$ensionlesspara$eters: lift and drag !oeffi!ients.

5rea A !an be frontal area drag appli!ations2%planfor$ area wing aerod#na$i!s2% or wetted+surfa!e area ship h#drod#na$i!s2.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow

E)a$ple: 5uto$obile Drag

4!ion * Drag for!e F D61-' ρ? ' CD 52 will be @ 1= ti$es larger for 4!ion *

> 4our!e is large C D and large pro e!ted area

>


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 1=

Drag and Lift

For appli!ations su!h as tapered wings%C L and C D $a# be a fun!tion of spanlo!ation. For these appli!ations% a lo!al

C L,x and C D,x are introdu!ed and the totallift and drag is deter$ined b# integrationover the span L


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BLofting a ,apered ing


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 1'

Fri!tion and


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4trea$lining

4trea$lining redu!es dragb# redu!ing F D%pressure % atthe !ost of in!reasingwetted surfa!e area andFD%fri!tion.

oal is to eli$inate flowseparation and $ini$iHetotal drag F D

5lso i$proves stru!turala!ousti!s sin!e separationand vorte) shedding !ane)!ite stru!tural $odes.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 1(

4trea$lining


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4trea$lining via 5!tive Flow Control


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 1/

C D of Co$$on eo$etries

For $an# geo$etries% total drag C D

is !onstant for Re J 1= ( C D !an be ver# dependent uponorientation of bod#.

5s a !rude appro)i$ation%superposition !an be used to addC D fro$ various !o$ponents of as#ste$ to obtain overall drag."owever% there is no $athe$ati!alreason e.g.% linear


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow '=

Flat


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow '1

Flat


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow ''

Effe!t of oughness

4i$ilar to Mood#Chart for pipe flowLa$inar flowunaffe!ted b#roughness,urbulent flowsignifi!antl# affe!ted:

Cf

!an in!rease b# 7)for a given e


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C#linder and 4phere Drag


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow '(

C#linder and 4phere Drag

Flow is strong fun!tion ofe.aIe narrows for

turbulent flow sin!e ,*Lturbulent boundar# la#er2

is $ore resistant toseparation due toadverse pressuregradient.

θ sep%la$ 8=θ sep%la$ 1(=


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Effe!t of 4urfa!e oughness


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow '/

Lift

Lift is the net for!edue to pressure andvis!ous for!es2perpendi!ular to flowdire!tion.Lift !oeffi!ient

A=bc is the planfor$area


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Co$puting Lift


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Effe!t of 5ngle of 5tta!I

,hin+foil theor# shows thatC L≈2 πα for α P α stall,herefore% lift in!reaseslinearl# with α

Ob e!tive for $ostappli!ations is to a!hieve$a)i$u$ C L /C D ratio.C D deter$ined fro$ wind+tunnel or CFD *LE or Q4E2.C L /C D in!reases up to order1==2 until stall.


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Effe!t of Foil 4hape

,hi!Iness and!a$ber influen!espressure distribution

and load distribution2and lo!ation of flowseparation.Foil database!o$piled b# 4elig

&9&C2http:--www.aae.uiu!.edu-$+selig-ads.ht$l

http://www.aae.uiuc.edu/m-selig/ads.htmlhttp://www.aae.uiuc.edu/m-selig/ads.htmlhttp://www.aae.uiuc.edu/m-selig/ads.htmlhttp://www.aae.uiuc.edu/m-selig/ads.html


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 3=

Effe!t of Foil 4hape

> Figures fro$ Q Color !ontours of

pressure field> 4trea$lines through

velo!it# field

> Ca$ber and thi!Iness shown

to have large i$pa!t on flowfield.


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End Effe!ts of ing ,ips

,ip vorte) !reated b#leaIage of flow fro$ high+pressure side to low+pressure side of wing.,ip vorti!es fro$ heav#air!raft persist fardownstrea$ and posedanger to light air!raft.

5lso sets taIeoff and

landing separation atbus# airports.


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 3'

End Effe!ts of ing ,ips

,ip effe!ts !an beredu!ed b# atta!hingendplates or winglets. ,rade+off betweenredu!ing indu!eddrag and in!reasingfri!tion drag.

ing+tip feathers onso$e birds serve thesa$e fun!tion.


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Lift enerated b# 4pinning

4uperposition of &nifor$ strea$ Doublet ?orte)


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Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow 3(

Lift enerated b# 4pinning

C L strongl# depends on rateof rotation.,he effe!t of rate of rotationon C D is s$all.

*aseball% golf% so!!er%tennis pla#ers utiliHe spin.Lift generated b# rotation is

!alled ,he Magnus Effe!t.

Drag Lift Variación II

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Transcript of Drag Lift Variación II