Is circulation real?

I think you may be confusing the title "professor". In the UK, the title "Professor" is conferred on the head of a faculty. Such a status is only granted to academics who have demonstrated the highest degree of academic competence. In the US, it appears anyone who teaches at a tertiary institution gets to call themselves a professor.
Holger Babinsky is Professor of Aerodynamics, Department of Engineering, University of Cambridge and has held that post for at least 10 years.
He both knows how to run a wind tunnel experiment and interpret the results.

 

This forum is a great research tool. I found this post (my emphasis) from 2004 on an old thread "Circulation" .

So why indeed are we still debating it?
Unfortunately I can't find a textbook or peer-reviewed paper that states it as clearly and concisely as you do here.

Anderson J.D. Fundamentals of Aerodynamics, gets close. After dedicating Section 2.13 to the subject and making many references later, he hedges his bets in Section 3.16 by saying:

"The circulation theory of lift is an alternative way of thinking about the generation of lift on an aerodynamic body. Keep in mind that the true physical sources of aerodynamic force on a body are the pressure and shear stress distributions exerted on the surface of the body, as explained in Section 1.5."

 

That is one seriously tortured proverb!

 

You keep on with personal attacks instead of well thought out responses. Doug's sources are not more hidden than those of the persons you quote. In science repeatability of experimental results is what makes a theory valid. A single source is not enough. Perhaps if you did some experiments and published your data, your position would be more credible. Simulations are not reality, regardless of how many graphs and numbers the computer generates.

 

How do you know? He hasn’t revealed his sources.

 

From that standard, neither have you. Your claim is that you have a code giving certain results. However, the code is not published for review.

 

I am happy to publish my code. It isn't being challenged.
I don't understand why my enquiry about @Doug Halsey's source of truth about the foundations of aerodynamics is such an issue.
Current version
The crucial line is
$pos += $velocity * $timeInt; // metres from LE
which is xn+1 = xn + Vn * Δt
Enjoy>

PHP:

<?php
//Ver 1 - make smoke 1/2 chord, 1 metre, not 1/4 so 200px
//Ver 2 - interpolate velocities between data points.
$ver = 2;
set_error_handler("customError");
$file = fopen('velocities.csv', 'r');
$velocities = array();
while (($velocities[] = fgetcsv($file)) !== FALSE) {
}
$screenWidth = 1100;
$screenHeight =700;
$im = imagecreate($screenWidth, $screenHeight);
$background_color = imagecolorallocate($im, 0, 0, 0);
$freeStreamColor =imagecolorallocate($im, 255,255,255);
$upperStreamColor =imagecolorallocate($im, 0,255,255 ); //cyan
$lowerStreamColor =imagecolorallocate($im, 255,0,255 ); // magenta
$wingColour =imagecolorallocate($im, 180,180,255 ); //pale blue
//imageline($im, 200,0, 200, $screenHeight, $freeStreamColor);
//imageline($im, 600,0, 600, $screenHeight, $freeStreamColor);
$thick = 5;
imagesetthickness($im, $thick);

//$x1= 100; $x2=200; $y1=100;
$upperFrontPosPx = 0; //distance down the track, of the front of the upper smoke Px from LE

$timeInt = 0.0001; // secs 0.1 millisecs
$baseSpeed = 10; //metres/sec
$velocityIndex = 0;
$time = 0;
$distRange = 0.02; //metres between measured velocities in the velocities table
$freeStreamFrontPx = 0; // position of front of free stream at normal speed
$prevFrame = 0;
$chordStart = 400; // px offset from left

//$upperSmokeFront = new Smoke(/*type*/0, $velocities, $timeInt, /*initPos*/ 0, $baseSpeed);
$delay = .25; // metres
$upperSmokeFront = array(
    "velocityIndex" => 0,
    "pos" => -$delay,
    "velocity"=>$baseSpeed
    );
$upperSmokeRear = array(
    "velocityIndex" => 0,
    "pos" => -(1+ $delay),
    "velocity"=>$baseSpeed
    );
$lowerSmokeFront = array(
    "velocityIndex" => 0,
    "pos" => -$delay,
    "velocity"=>$baseSpeed
    );
$lowerSmokeRear = array(
    "velocityIndex" => 0,
    "pos" => -(1+ $delay),
    "velocity"=>$baseSpeed
    );
$cycle=0;
while ($freeStreamFrontPx < 680){ // metres of the wing chord of freestream
        $cycle++;
    $currentFrame = round($time *20+.5);
    $freeStreamFrontPx += 200*$baseSpeed *$timeInt;// position at base speed
    $upperSmokeFront = calcNextPos (1,$upperSmokeFront);
    $upperSmokeRear = calcNextPos (1,$upperSmokeRear);
    $lowerSmokeFront = calcNextPos (2,$lowerSmokeFront);
    $lowerSmokeRear = calcNextPos (2,$lowerSmokeRear);

    $y = 100*($currentFrame-1);
    $timeFormatted = round($time*100)/100;
    if ($currentFrame <> $prevFrame ){
        imagestring($im,5,10,$y +10,"Frame:". $currentFrame. " time: $timeFormatted secs." ,$freeStreamColor);
        imagedashedline($im , 0, $y, $screenWidth, $y, $freeStreamColor);
        $prevFrame =$currentFrame;
        //value in $upperFrontPosPx is metres from the start of the chord. 1 metre = 200 px
/******** freeStream ***********/
        $y  += 30; // vertical separation

        $x1 = $chordStart - 200 + $freeStreamFrontPx ;
        $x2 = $chordStart + $freeStreamFrontPx ;
        imageline($im , $x1, $y, $x2, $y, $freeStreamColor);
        //imagestring($im,2,$x1-80,$y - 5,
        imagestring($im,2,20,$y - 5,
            "Free stream",
            $freeStreamColor
        );
/******** upper smoke ***********/
        //print_r($upperSmokeFront);
        $upperSmokeFrontPx = 200*$upperSmokeFront["pos"] ;
        $upperSmokeRearPx = 200*$upperSmokeRear["pos"] ;
        //print "upperSmokeRearPx $upperSmokeRearPx\n";
        $y  += 10;
       
        $x1 =  $chordStart + $upperSmokeRearPx; //$upperSmokeFrontPx - 100  ; //100px
        //$x1 =  $upperRearPosPx ;
        $x2 =  $chordStart + $upperSmokeFrontPx;
        imageline($im , $x1, $y, $x2, $y, $upperStreamColor);
        imagestring($im,2,20,$y - 5,
            "Upper stream",
            $upperStreamColor
        );
/******** wing *************/
        $y  += 15;
        imagestring($im,4,100,$y - 5,"WING",$wingColour);
        $x1 =  $chordStart ;
        $x2 =  $chordStart + 400 ;
        imagesetthickness($im, 10);
        imageline($im , $x1, $y, $x2, $y, $wingColour);
/******** lower smoke ***********/
        //print_r($lowerSmokeFront);
        $lowerSmokeFrontPx = 200*$lowerSmokeFront["pos"] ;
        $lowerSmokeRearPx = 200*$lowerSmokeRear["pos"] ;
        //print "lowerSmokeRearPx $lowerSmokeRearPx\n";
        $y  += 15;
       
        $x1 =  $chordStart + $lowerSmokeRearPx; //$lowerSmokeFrontPx - 100  ; //100px
        //$x1 =  $lowerRearPosPx ;
        $x2 =  $chordStart + $lowerSmokeFrontPx;
        imagesetthickness($im, $thick);

        imageline($im , $x1, $y, $x2, $y, $lowerStreamColor);
        print round($time *25+.5)."  time,". round($time*100)/100 .",lowerSmokeRearPx,". round($lowerSmokeRearPx).",lowerSmokeFrontPx,". round($lowerSmokeFrontPx)."\n";
        imagestring($im,2,20,$y - 5,"Lower stream",$lowerStreamColor
        );
/******** freeStream ***********/
        $y  += 10; // vertical separation
        $x1 = $chordStart - 200 + $freeStreamFrontPx ;
        $x2 = $chordStart + $freeStreamFrontPx ;
        imageline($im , $x1, $y, $x2, $y, $freeStreamColor);
        imagestring($im,2,20,$y - 5,"Free stream",$freeStreamColor
        );

    }
    $fileName ="velocity".$ver.".png";
        imagepng($im, $fileName);//exit;
        imageDestroy($im);
       
    //if (intval($time *100) % 10 == 0){
    //print round($time *25+.5)." ". ($time *25) ." time, $time , pos, $upperFrontPosPx, $freeStreamFrontPx\n";//, velocityIndex, $velocityIndex velocity, $velocity, positionAsPartOfCurrentDistRange, $upperFrontPosPxitionAsPartOfCurrentDistRange, velocityGrad, $velocityGrad \n";
    //}
    $time = $time + $timeInt;
    if ($time > .1){
        //exit;
    }
   
}
print "cycle: $cycle\n";


// can't get OO to work, back to functiona and arrays.
function calcNextPos($smokeIndex,$smoke){ // working in metres and m/sec
    global $timeInt, $velocities,$baseSpeed ,$distRange;
    //print "HELLO\n";
    $pos = $smoke["pos"];
    $velocityIndex =$smoke["velocityIndex"];
    $velocity = $smoke["velocity"]; // previously calculated (or initial for step0)
   
    $deltaX = $velocity * $timeInt;
//print "velocityIndex $velocityIndex \n";exit;
    $pos +=  $velocity * $timeInt;  // metres from LE
    if ($pos <0){ // use free stream velocity
        $velocity = $baseSpeed;
        //$pos +=  $velocity * $timeInt;  // metres from LE //echo "using baseSpeed $velocity pos $pos\n";
    }
    else{
        if (isset($velocities[$velocityIndex+1][0])){ //position of front of upper airflow
            if ($pos > $velocities[$velocityIndex+1][0] ){ //still not found
                $velocityIndex ++;
                if ($pos > $velocities[$velocityIndex+1][0]) { //we've skipped an interval so rethink the time intervals
                    print "velocityIndex $velocityIndex rethink the intervals!\n"; exit; }
            }
            $nextIndex = $velocityIndex+1;
            $partOfCurrentDistRange = ($pos - $velocities[$velocityIndex][0]) /$distRange;// distance down this segment
            $vStep = $velocities[$nextIndex][$smokeIndex]  - $velocities[$velocityIndex][$smokeIndex]; // delta V between start and end of delta x
            $deltaV = $vStep *$partOfCurrentDistRange;
            $velocity = $velocities[$velocityIndex][$smokeIndex] +$deltaV; // new velocity
            if ($smokeIndex ==2){ //lower
                //print "lower partOfCurrentDistRange $partOfCurrentDistRange velocity $velocity\n";
            }
        }
        else{$nextIndex = $velocityIndex;} // past the end so constant velocity
       
    }
   
    $smoke["velocity"] = $velocity;
    //print "velocityIndex $velocityIndex velocity $velocity pos $pos \n";
    $posPx =200*$pos ;// returns Px from LE
    //print "pos: $pos\n";
    $smoke["pos"] = $pos;
    $smoke["velocityIndex"] = $velocityIndex;
    //print_r($smoke);
    return $smoke ;// returns Px from LE
}

    function customError($errno, $errstr) {
        echo "Error:[$errno] $errstr\n";
        //exit;
    }
?>


 

How far apart are the data points you interpolate?

 

I digitised the data from @Doug Halsey's grid at 0.01 intervals (the first 90 points to .9 after which the data gets a bit wonky! (see my post#432)
separately for the upper and lower surfaces: (col 1 is metres along the 2 metre chord)
0.00,15.0,15.0
0.02,23.3,4.5
0.04,22.7,0.7
0.06,22.0,1.5
0.08,21.0,3.0
0.10,20.5,4.0
....
and interpolate between the points as a straight line.

 

I forgot to ask. Why do you want to know?

 

It matters how far apart point are when interpolating. Is the first number the interval? I interpret that as one point every 2cm.

 

Yes, every 2 cm of the first 1.8 metres of the 2 metre chord length. That was the grid size of the graph I was digitising.

 

@Alan Cattelliot and Doug. It seems to me that the spacing may be too coarse. It is possibly larger than the boundary layer if I am not mistaken.

 

OK, in the absence of a response by the addressees, I'll ask the question.
Why would the quality of the data be compromised by the relationship between the spacing of the data points (along the chord) and the thickness of the boundary layer (perp to the chord)?

 

The quality of the data is not the issue. If the boundary layer is thinner than the spacing between data points, then you can't calculate much about it. For a statistical value, you need at least three points at the area of interest.