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Merge pull request #2066 from JoePfeiffer/fix-tubefins

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Fix interstices area calculation and update pressure drag calculation for tube fins
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Joe Pfeiffer 2023-07-02 16:51:13 -06:00 committed by GitHub
commit d2c20bd90f
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4 changed files with 96 additions and 80 deletions
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65
core/src/net/sf/openrocket/aerodynamics/barrowman/TubeCalc.java
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@ -14,73 +14,64 @@ public abstract class TubeCalc extends RocketComponentCalc {
private final static Logger log = LoggerFactory.getLogger(TubeFinSetCalc.class);
// air density (standard conditions)
private final double rho = 1.225; // kg/m^3
private final Tube tube;
private final double diameter;
private final double length;
protected final double innerArea;
private final double totalArea;
private final double frontalArea;
private final double epsilon;
public TubeCalc(RocketComponent component) {
super(component);
Tube tube = (Tube)component;
tube = (Tube)component;
length = tube.getLength();
diameter = 2 * tube.getInnerRadius();
innerArea = Math.PI * MathUtil.pow2(tube.getInnerRadius());
totalArea = Math.PI * MathUtil.pow2(tube.getOuterRadius());
frontalArea = totalArea - innerArea;
epsilon = tube.getFinish().getRoughnessSize(); // roughness; note we don't maintain surface roughness of
// interior separately from exterior.
}
@Override
public double calculatePressureCD(FlightConditions conditions,
double stagnationCD, double baseCD, WarningSet warnings) {
// These calculations come from a mix of theoretical and empirical
// results, and are marked with (t) for theoretical and (e) for empirical.
// The theoretical results should not be modified; the empirical can be adjusted
// to better simulate real rockets as we get data.
// For the sources of the empirical formulas, see Carello, Ivanov, and Mazza,
// "Pressure drop in pipe lines for compressed air: comparison between experimental
// and theoretical analysis", Transactions on Engineering Sciences vol 18,
// ISSN 1743-35331998, 1998.
// For the rockets for which we have data, the effect of the stagnation CD appears to be
// overstated. This code multiplies it be a factor of 0.7 to better match experimental
// data
// Need to check for tube inner area 0 in case of rockets using launch lugs with
// an inner radius of 0 to emulate rail buttons (or just weird rockets, of course)
// an inner radius of 0 to emulate rail guides (or just weird rockets, of course)
double tubeCD = 0.0;
double deltap;
if (innerArea > MathUtil.EPSILON) {
// Temperature
final double T = conditions.getAtmosphericConditions().getTemperature();
// Volume flow rate (t)
final double Q = conditions.getVelocity() * innerArea;
// Current atmospheric conditions
final double p = conditions.getAtmosphericConditions().getPressure();
final double t = conditions.getAtmosphericConditions().getTemperature();
final double rho = conditions.getAtmosphericConditions().getDensity();
final double v = conditions.getVelocity();
// Reynolds number (note Reynolds number for the interior of a pipe is based on diameter,
// not length (t))
final double Re = conditions.getVelocity() * diameter /
conditions.getAtmosphericConditions().getKinematicViscosity();
final double Re = v * diameter / conditions.getAtmosphericConditions().getKinematicViscosity();
// friction coefficient (for smooth tube interior) (e)
final double lambda = 1/MathUtil.pow2(2 * Math.log(0.5625 * Math.pow(Re, 0.875)) - 0.8);
// pressure drop (e)
final double P0 = 100; // standard pressure
final double T0 = 273.15; // standard temperature
deltap = (lambda * 8 * length * rho * MathUtil.pow2(Q) * T * P0) /
(MathUtil.pow2(Math.PI) * Math.pow(diameter, 5) * T0 * conditions.getAtmosphericConditions().getPressure());
} else {
deltap = 0.0;
// friction coefficient using Swamee-Jain equation
double f = 0.25/MathUtil.pow2(Math.log10((epsilon / (3.7 * diameter) + 5.74/Math.pow(Re, 0.9))));
// If we're supersonic, apply a correction
if (conditions.getMach() > 1) {
f = f / conditions.getBeta();
}
// pressure drop using Darcy-Weissbach equation
deltap = f * (length * rho * MathUtil.pow2(v)) / (2 * diameter);
// drag coefficient of tube interior from pressure drop
tubeCD = 2 * (deltap * innerArea) / (rho * MathUtil.pow2(v) * innerArea);
}
// convert to CD and return
return (deltap * innerArea + 0.7 * stagnationCD * frontalArea) / conditions.getRefArea();
final double cd = (tubeCD * innerArea + 0.7*(stagnationCD + baseCD) * frontalArea) / conditions.getRefArea();
return cd;
}
}

88
core/src/net/sf/openrocket/aerodynamics/barrowman/TubeFinSetCalc.java
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@ -25,6 +25,8 @@ public class TubeFinSetCalc extends TubeCalc {
private static final double STALL_ANGLE = (20 * Math.PI / 180);
private final double[] poly = new double[6];
private final TubeFinSet tubes;
// parameters straight from configuration; we'll be grabbing them once
// so code is a bit shorter elsewhere
@ -44,14 +46,14 @@ public class TubeFinSetCalc extends TubeCalc {
private final double cnaconst;
protected final WarningSet geometryWarnings = new WarningSet();
public TubeFinSetCalc(RocketComponent component) {
super(component);
if (!(component instanceof TubeFinSet)) {
throw new IllegalArgumentException("Illegal component type " + component);
}
final TubeFinSet tubes = (TubeFinSet) component;
tubes = (TubeFinSet) component;
if (tubes.getTubeSeparation() > MathUtil.EPSILON) {
geometryWarnings.add(Warning.TUBE_SEPARATION);
@ -75,37 +77,53 @@ public class TubeFinSetCalc extends TubeCalc {
// aspect ratio.
ar = 2 * innerRadius / chord;
// Some trigonometry...
// We need a triangle with the following three sides:
// d is from the center of the body tube to a tangent point on the tube fin
// outerRadius is from the center of the tube fin to the tangent point. Note that
// d and outerRadius are at right angles
// bodyRadius + outerRadius is from the center of the body tube to the center of the tube fin.
// This is the hypotenuse of the right triangle.
// Find length of d
final double d = Math.sqrt(MathUtil.pow2(bodyRadius + outerRadius) - MathUtil.pow2(outerRadius));
// Area of diamond formed by mirroring triangle on its hypotenuse (same area as rectangle
// formed by d and outerarea, but it *isn't* that rectangle)
double a = d * outerRadius;
// angle between outerRadius and bodyRadius+outerRadius
final double theta1 = Math.acos(outerRadius/(outerRadius + bodyRadius));
// area of arc from tube fin, doubled to get both halves of diamond
final double a1 = MathUtil.pow2(outerRadius) * theta1;
// angle between bodyRadius+outerRadius and d
final double theta2 = Math.PI/2.0 - theta1;
// area of arc from body tube. Doubled so we have area to remove from diamond
final double a2 = MathUtil.pow2(bodyRadius) * theta2;
// area of interstice for one tube fin
intersticeArea = (a - a1 - a2);
// for comparison, what's the area of a tube fin?
double tubeArea = MathUtil.pow2(outerRadius) * Math.PI;
// wetted area for friction drag calculation. We don't consider the inner surface of the tube;
// that affects the pressure drop through the tube and so (indirecctly) affects the pressure drag.
// Area of the outer surface of tubes. Since roughly half
// of the area is "masked" by the interstices between the tubes and the
// body tube, only consider the other half of the area (so only multiplying by pi instead of 2*pi)
final double outerArea = chord * Math.PI * outerRadius;
// Area of the outer surface of a tube, not including portion masked by interstice
final double outerArea = chord * 2.0 * (Math.PI - theta1) * outerRadius;
// Surface area of the portion of the body tube masked by the tube fins, per tube
final BodyTube parent = (BodyTube) tubes.getParent();
final double maskedArea = chord * 2.0 * Math.PI * bodyRadius / tubeCount;
// Surface area of the portion of the body tube masked by the tube fin. We'll subtract it from
// the tube fin area rather than go in and change the body tube surface area calculation. If tube
// fin and body tube roughness aren't the same this will result in an inaccuracy.
final double maskedArea = chord * 2.0 * theta2 * bodyRadius;
wettedArea = outerArea - maskedArea;
log.debug("wetted area of tube fins " + wettedArea);
// frontal area of interstices between tubes for pressure drag calculation.
// We'll treat them as a closed blunt object.
// area of disk passing through tube fin centers
final double tubeDiskArea = Math.PI * MathUtil.pow2(bodyRadius + outerRadius);
// half of combined area of tube fin exteriors. Deliberately using the outer radius here since we
// calculate pressure drag from the tube walls in TubeCalc
final double tubeOuterArea = tubeCount * Math.PI * MathUtil.pow2(outerRadius) / 2.0;
// body tube area
final double bodyTubeArea = Math.PI * MathUtil.pow2(bodyRadius);
// area of an interstice
intersticeArea = (tubeDiskArea - tubeOuterArea - bodyTubeArea) / tubeCount;
// Precompute most of CNa. Equation comes from Ribner, "The ring airfoil in nonaxial
// flow", Journal of the Aeronautical Sciences 14(9) pp 529-530 (1947) equation (5).
@ -246,10 +264,8 @@ public class TubeFinSetCalc extends TubeCalc {
@Override
public double calculateFrictionCD(FlightConditions conditions, double componentCf, WarningSet warnings) {
warnings.addAll(geometryWarnings);
final double frictionCD = componentCf * wettedArea / conditions.getRefArea();
final double frictionCD = componentCf * wettedArea / conditions.getRefArea();
return frictionCD;
}
@ -258,18 +274,10 @@ public class TubeFinSetCalc extends TubeCalc {
double stagnationCD, double baseCD, WarningSet warnings) {
warnings.addAll(geometryWarnings);
final double cd = super.calculatePressureCD(conditions, stagnationCD, baseCD, warnings) +
(stagnationCD + baseCD) * intersticeArea / conditions.getRefArea();
(stagnationCD + baseCD) * intersticeArea / conditions.getRefArea();
return cd;
}
private static int calculateInterferenceFinCount(TubeFinSet component) {
RocketComponent parent = component.getParent();
if (parent == null) {
throw new IllegalStateException("fin set without parent component");
}
return 3 * component.getFinCount();
}
}

15
core/src/net/sf/openrocket/rocketcomponent/BodyTube.java
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@ -550,4 +550,19 @@ public class BodyTube extends SymmetricComponent implements BoxBounded, MotorMou
// The motor config also has listeners, so clear them as well
getDefaultMotorConfig().clearConfigListeners();
}
/**
* The first time we add a TubeFinSet to the component tree, inherit the tube thickness from
* the parent body tube
*/
@Override
public final void addChild(RocketComponent component, int index, boolean trackStage) {
super.addChild(component, index, trackStage);
if (component instanceof TubeFinSet) {
TubeFinSet finset = (TubeFinSet) component;
if (Double.isNaN(finset.getThickness())) {
finset.setThickness(getThickness());
}
}
}
}

8
core/src/net/sf/openrocket/rocketcomponent/TubeFinSet.java
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@ -24,7 +24,7 @@ public class TubeFinSet extends Tube implements AxialPositionable, BoxBounded, R
private boolean autoRadius = true; // Radius chosen automatically based on parent component
private double outerRadius = DEFAULT_RADIUS;
protected double thickness = 0.002;
protected double thickness = Double.NaN;
private AngleMethod angleMethod = AngleMethod.FIXED;
protected RadiusMethod radiusMethod = RadiusMethod.RELATIVE;
@ -49,7 +49,7 @@ public class TubeFinSet extends Tube implements AxialPositionable, BoxBounded, R
/**
* New FinSet with given number of fins and given base rotation angle.
* New TubeFinSet with default values
* Sets the component relative position to POSITION_RELATIVE_BOTTOM,
* i.e. fins are positioned at the bottom of the parent component.
*/
@ -146,6 +146,7 @@ public class TubeFinSet extends Tube implements AxialPositionable, BoxBounded, R
* Sets whether the radius is selected automatically or not.
*/
public void setOuterRadiusAutomatic(boolean auto) {
for (RocketComponent listener : configListeners) {
if (listener instanceof TubeFinSet) {
((TubeFinSet) listener).setOuterRadiusAutomatic(auto);
@ -195,8 +196,9 @@ public class TubeFinSet extends Tube implements AxialPositionable, BoxBounded, R
if ((this.thickness == thickness))
return;
this.thickness = MathUtil.clamp(thickness, 0, getOuterRadius());
fireComponentChangeEvent(ComponentChangeEvent.MASS_CHANGE);
fireComponentChangeEvent(ComponentChangeEvent.BOTH_CHANGE);
clearPreset();
}