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Refinements to calculation of tube drag

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This commit is contained in:
JoePfeiffer 2023-06-30 10:09:00 -06:00
parent a3aebadcff
commit d5291d7b52
2 changed files with 8 additions and 19 deletions
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11
core/src/net/sf/openrocket/aerodynamics/barrowman/TubeCalc.java
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@ -59,22 +59,19 @@ public abstract class TubeCalc extends RocketComponentCalc {
double f = 0.25/MathUtil.pow2(Math.log10((epsilon / (3.7 * diameter) + 5.74/Math.pow(Re, 0.9)))); 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 we're supersonic, apply a correction
// if (conditions.getMach() > 1) { if (conditions.getMach() > 1) {
// f = f / conditions.getBeta(); f = f / conditions.getBeta();
// } }
// pressure drop using Darcy-Weissbach equation // pressure drop using Darcy-Weissbach equation
deltap = f * (length * rho * MathUtil.pow2(v)) / (2 * diameter); deltap = f * (length * rho * MathUtil.pow2(v)) / (2 * diameter);
System.out.println(tube + ", v " + v + ", Re " + Re + ", p " + p + ": " + "deltap " + deltap);
// drag coefficient of tube interior from pressure drop // drag coefficient of tube interior from pressure drop
tubeCD = 2 * (deltap * innerArea) / (rho * MathUtil.pow2(v) * innerArea); tubeCD = 2 * (deltap * innerArea) / (rho * MathUtil.pow2(v) * innerArea);
} }
// convert to CD and return // convert to CD and return
System.out.println(tube + " tube CD " + tubeCD + ", stagnationCD " + stagnationCD + ", baseCD " + baseCD + ", inner area " + innerArea + ", frontal area " + frontalArea); final double cd = (tubeCD * innerArea + 0.7*(stagnationCD + baseCD) * frontalArea) / conditions.getRefArea();
final double cd = (tubeCD * innerArea + (stagnationCD + baseCD) * frontalArea) / conditions.getRefArea();
System.out.println(tube + " cd " + cd);
return cd; return cd;
} }
} }

16
core/src/net/sf/openrocket/aerodynamics/barrowman/TubeFinSetCalc.java
View File

@ -102,7 +102,6 @@ public class TubeFinSetCalc extends TubeCalc {
// angle between bodyRadius+outerRadius and d // angle between bodyRadius+outerRadius and d
final double theta2 = Math.PI/2.0 - theta1; final double theta2 = Math.PI/2.0 - theta1;
System.out.println("theta2 " + theta2);
// area of arc from body tube. Doubled so we have area to remove from diamond // area of arc from body tube. Doubled so we have area to remove from diamond
final double a2 = MathUtil.pow2(bodyRadius) * theta2; final double a2 = MathUtil.pow2(bodyRadius) * theta2;
@ -118,18 +117,13 @@ public class TubeFinSetCalc extends TubeCalc {
// Area of the outer surface of a tube, not including portion masked by interstice // Area of the outer surface of a tube, not including portion masked by interstice
final double outerArea = chord * 2.0 * (Math.PI - theta1) * outerRadius; final double outerArea = chord * 2.0 * (Math.PI - theta1) * outerRadius;
// Area of inner surface of a tube
final double innerArea = chord * 2.0 * Math.PI * innerRadius;
// Surface area of the portion of the body tube masked by the tube fin. We'll subtract it from // 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 // 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. // fin and body tube roughness aren't the same this will result in an inaccuracy.
final double maskedArea = chord * 2.0 * theta2 * bodyRadius; final double maskedArea = chord * 2.0 * theta2 * bodyRadius;
wettedArea = innerArea + outerArea - maskedArea; wettedArea = outerArea - maskedArea;
System.out.println(tubes + " outer " + outerArea + ", masked " + maskedArea);
log.debug("wetted area of tube fin " + wettedArea);
// Precompute most of CNa. Equation comes from Ribner, "The ring airfoil in nonaxial // 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). // flow", Journal of the Aeronautical Sciences 14(9) pp 529-530 (1947) equation (5).
@ -270,9 +264,8 @@ public class TubeFinSetCalc extends TubeCalc {
@Override @Override
public double calculateFrictionCD(FlightConditions conditions, double componentCf, WarningSet warnings) { public double calculateFrictionCD(FlightConditions conditions, double componentCf, WarningSet warnings) {
System.out.println(tubes + "wetted area " + wettedArea);
final double frictionCD = componentCf * wettedArea / conditions.getRefArea(); final double frictionCD = componentCf * wettedArea / conditions.getRefArea();
return frictionCD; return frictionCD;
} }
@ -281,11 +274,10 @@ public class TubeFinSetCalc extends TubeCalc {
double stagnationCD, double baseCD, WarningSet warnings) { double stagnationCD, double baseCD, WarningSet warnings) {
warnings.addAll(geometryWarnings); warnings.addAll(geometryWarnings);
System.out.println(tubes + " stag CD " + stagnationCD + ", base CD " + baseCD);
final double cd = super.calculatePressureCD(conditions, stagnationCD, baseCD, warnings) + final double cd = super.calculatePressureCD(conditions, stagnationCD, baseCD, warnings) +
(stagnationCD + baseCD) * intersticeArea / conditions.getRefArea(); (stagnationCD + baseCD) * intersticeArea / conditions.getRefArea();
return cd; return cd;
} }
} }