def test_getReynoldsNumber(self):
environment = self.environment.getAirProperties(Vector(0,0,0))
self.assertAlmostEqual(AeroParameters.getReynoldsNumber(self.rocketState1, environment, 1), 13701279.02972, 2)
def _getAppliedForce(self, time, state):
''' Get the total force currently being experienced by the rocket, used by self.rigidBody to calculate the rocket's acceleration '''
### Precomputations and Logging ###
environment = self._getEnvironmentalConditions(time, state) # Get and log current air/wind properties
rocketInertia = self.getInertia(time, state) # Get and log current rocket inertia
if self.derivativeEvaluationLog is not None:
self.derivativeEvaluationLog.newLogRow(time)
self.derivativeEvaluationLog.logValue("Position(m)", state.position)
self.derivativeEvaluationLog.logValue("Velocity(m/s)", state.velocity)
### Component Forces ###
if not self.isUnderChute:
# Precompute and log
Mach = AeroParameters.getMachNumber(state, environment)
unitRe = AeroParameters.getReynoldsNumber(state, environment, 1.0)
AOA = AeroParameters.getTotalAOA(state, environment)
rollAngle = AeroParameters.getRollAngle(state, environment)
if self.derivativeEvaluationLog is not None:
self.derivativeEvaluationLog.logValue("Mach", Mach)
self.derivativeEvaluationLog.logValue("UnitRe", unitRe)
self.derivativeEvaluationLog.logValue("AOA(deg)", math.degrees(AOA))
self.derivativeEvaluationLog.logValue("RollAngle(deg)", rollAngle)
self.derivativeEvaluationLog.logValue("OrientationQuaternion", state.orientation)
self.derivativeEvaluationLog.logValue("AngularVelocity(rad/s)", state.angularVelocity)
# This function will be the inherited function CompositeObject.getAppliedForce
componentForces = self.getAppliedForce(state, time, environment, rocketInertia.CG)
else:
# When under chute, neglect forces from other components
componentForces = self.recoverySystem.getAppliedForce(state, time, environment, Vector(0,0,-1))
# Log the recovery system's applied force (Normally handled in CompositeObject.getAppliedForce)
if hasattr(self.recoverySystem, "forcesLog"):
self.recoverySystem.forcesLog.append(componentForces.force)
self.recoverySystem.momentsLog.append(componentForces.moment)
# Move Force-Moment system to rocket CG
componentForces = componentForces.getAt(rocketInertia.CG)
### Gravity ###
gravityForce = self.environment.getGravityForce(rocketInertia, state)
totalForce = componentForces + gravityForce
### Launch Rail ###
totalForce = self.environment.applyLaunchTowerForce(state, time, totalForce)
if self.derivativeEvaluationLog is not None:
self.derivativeEvaluationLog.logValue("Wind(m/s)", environment.Wind)
self.derivativeEvaluationLog.logValue("AirDensity(kg/m^3)", environment.Density)
self.derivativeEvaluationLog.logValue("CG(m)", rocketInertia.CG)
self.derivativeEvaluationLog.logValue("MOI(kg*m^2)", rocketInertia.MOI)
self.derivativeEvaluationLog.logValue("Mass(kg)", rocketInertia.mass)
CPZ = AeroFunctions._getCPZ(componentForces)
self.derivativeEvaluationLog.logValue("CPZ(m)", CPZ)
self.derivativeEvaluationLog.logValue("AeroF(N)", componentForces.force)
self.derivativeEvaluationLog.logValue("AeroM(Nm)", componentForces.moment)
self.derivativeEvaluationLog.logValue("GravityF(N)", gravityForce.force)
self.derivativeEvaluationLog.logValue("TotalF(N)", totalForce.force)
return totalForce
def getSkinFrictionCoefficient(state,
environment,
length,
Mach,
surfaceRoughness,
assumeFullyTurbulent=True):
'''
Calculates the skin friction drag coefficient (normalized by wetted area, not cross-sectional area).
Uses the methods described in (Barrowman, 1967, pg. 43-48) and in (Niskanen, 2009, pg. 43-46)
Used for skin friction calculations for all external rocket components
Inputs:
* state: (RigidBodyState)
* environment: (EnvironmentalConditions)
* length: (float) - reference length for the current rocket component, used for Reynolds number calculation
* Mach: (float) - current Mach number
* surfaceRoughness (float) - micrometers
Outputs:
* Returns the skin friction coefficient normalized by **wetted area**, must be converted to be normalized by cross-sectional area before summing with other coefficients.
'''
Re = AeroParameters.getReynoldsNumber(state, environment, length)
smoothSurface = (surfaceRoughness == 0) # True or False
if smoothSurface:
# Very large (unreachable) number
criticalRe = 1e100
else:
criticalRe = 51 * (surfaceRoughness / length)**(
-1.039) # Eqn 4-7 (Barrowman)
# Get skin friction factor (Mach number independent)
if Re > criticalRe:
# Re is above Critical value
# Friction determined by roughness
skinFrictionCoefficient = 0.032 * (surfaceRoughness / length)**0.2
elif assumeFullyTurbulent:
if Re < 1e4:
# Limit for low Reynolds numbers
skinFrictionCoefficient = 0.0148 # Eqn 3.81 (Niskanen) - match up with turbulent flow correlation
else:
# Eqn from Niskanen
skinFrictionCoefficient = 1 / ((1.5 * math.log(Re) - 5.6)**2)
else:
# Laminar / Transitional flow
if Re < 1e4:
# Limit for low Reynolds numbers
skinFrictionCoefficient = 0.01328 # Match up with transitional flow eqn
elif Re < 5e5:
# Laminar flow
skinFrictionCoefficient = 1.328 / math.sqrt(
Re) # Eqn 4-2 (Barrowman)
else:
# Transitional Flow
skinFrictionCoefficient = 1 / (
(1.5 * math.log(Re) - 5.6)**2
) - 1700 / Re # Eqn 4-6 (Barrowman), subtraction term from from Prandtl
# Calculate compressibility correction
if Mach < 0.9:
# Subsonic
compressibilityCorrectionFactor = _subSonicSkinFrictionCompressiblityCorrectionFactor(
Mach, smoothSurface)
elif Mach < 1.1:
# Transonic
subsonicFactor = _subSonicSkinFrictionCompressiblityCorrectionFactor(
Mach, smoothSurface)
supersonicFactor = _supersonicSkinFrictionCompressiblityCorrectionFactor(
Mach, smoothSurface)
# Linearly interpolate in the Mach 0.9-1.1 region - same method as that used in OpenRocket v15.03
compressibilityCorrectionFactor = subsonicFactor + (
(supersonicFactor - subsonicFactor) * (Mach - 0.9) / 0.2)
else:
# Supersonic
compressibilityCorrectionFactor = _supersonicSkinFrictionCompressiblityCorrectionFactor(
Mach, smoothSurface)
# Return corrected factor
return skinFrictionCoefficient * compressibilityCorrectionFactor