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More detailed model for pressure drop in tubes.

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This commit is contained in:
JoePfeiffer 2022-05-04 07:04:01 -06:00
parent 30dcdda0bf
commit 1611fd2876
1 changed files with 37 additions and 9 deletions
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46
core/src/net/sf/openrocket/aerodynamics/barrowman/TubeCalc.java
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@ -6,8 +6,17 @@ import net.sf.openrocket.rocketcomponent.RocketComponent;
import net.sf.openrocket.rocketcomponent.Tube;
import net.sf.openrocket.util.MathUtil;
public abstract class TubeCalc extends RocketComponentCalc {
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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 double diameter;
private final double length;
protected double refArea;
@ -25,18 +34,37 @@ public abstract class TubeCalc extends RocketComponentCalc {
@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.
// calculation of pressure drop through pipe from "Atlas Copco Air Compendium", 1975,
// quoted as equation 14 in Carello, Ivanov, and Mazza, "Pressure drop in pipe
// Temperature
final double T = conditions.getAtmosphericConditions().getTemperature();
// Sutherland Equation for viscosity of air (e)
final double mu = 1.458e-6 * Math.pow(T, 3/2) / (T + 110.4); //
// Volume flow rate (t)
final double Q = conditions.getVelocity() * refArea;
// Reynolds number (note Reynolds number for the interior of a pipe is based on diameter,
// not length (t)
final double Re = (4 * rho * Q) / (Math.PI * diameter * mu);
// quoted as equation 12 in 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.
// Volume flow rate
final double Q = conditions.getVelocity() * refArea;
// pressure drop
final double deltap = 1.6 * Math.pow(Q, 1.85) * length /
(Math.pow(diameter, 5) * conditions.getAtmosphericConditions().getPressure());
// friction coefficient (for tube interior) (e)
final double lambda = 0.3164 * Math.pow(Re, -0.25);
// pressure drop (e)
// 101.325 is standard pressure
// Power in equation is 5 in original source. That was experimentally derived; I'm adjusting
// it to match the data I've got from two rockets.
final double deltap = (lambda * 8 * length * rho * MathUtil.pow2(Q) * T * 101.325) /
(MathUtil.pow2(Math.PI) * Math.pow(diameter, 4.8) * 273 * conditions.getAtmosphericConditions().getPressure());
// convert to CD and return
return deltap * refArea / conditions.getRefArea();