Flow Separation Warning (#205)

If the simulation shows an exit pressure which is below the Summerfield Criteria for flow separation, a warning will be generated.

motorlib/motor.py

@@ -17,12 +17,15 @@ def __init__(self):
         self.props['maxPressure'] = FloatProperty('Maximum Allowed Pressure', 'Pa', 0, 7e7)
         self.props['maxMassFlux'] = FloatProperty('Maximum Allowed Mass Flux', 'kg/(m^2*s)', 0, 1e4)
         self.props['minPortThroat'] = FloatProperty('Minimum Allowed Port/Throat Ratio', '', 1, 4)
+        self.props['flowSeparationWarnPercent'] = FloatProperty('Flow Separation Warning Threshold', '', 0.00, 1)
         # Simulation
         self.props['burnoutWebThres'] = FloatProperty('Web Burnout Threshold', 'm', 2.54e-5, 3.175e-3)
         self.props['burnoutThrustThres'] = FloatProperty('Thrust Burnout Threshold', '%', 0.01, 10)
         self.props['timestep'] = FloatProperty('Simulation Timestep', 's', 0.0001, 0.1)
         self.props['ambPressure'] = FloatProperty('Ambient Pressure', 'Pa', 0.0001, 102000)
         self.props['mapDim'] = IntProperty('Grain Map Dimension', '', 250, 2000)
+        self.props['sepPressureRatio'] = FloatProperty('Separation Pressure Ratio', '', 0.001, 1)
+
 
 
 class Motor():
@@ -280,6 +283,11 @@ def runSimulation(self, callback=None):
             alert = SimAlert(SimAlertLevel.WARNING, SimAlertType.CONSTRAINT, desc, 'Motor')
             simRes.addAlert(alert)
 
+        if (simRes.getPercentBelowThreshold('exitPressure', self.config.getProperty('ambPressure') * self.config.getProperty('sepPressureRatio')) > self.config.getProperty('flowSeparationWarnPercent')):
+            desc = 'Low exit pressure, nozzle flow may separate'
+            alert = SimAlert(SimAlertLevel.WARNING, SimAlertType.VALUE, desc, 'Nozzle')
+            simRes.addAlert(alert)
+
         # Note that this only adds all errors found on the first datapoint where there were errors to avoid repeating
         # errors. It should be revisited if getPressureErrors ever returns multiple types of errors
         for pressure in simRes.channels['pressure'].getData():

motorlib/simResult.py

@@ -90,6 +90,13 @@ def getMax(self):
         if self.valueType in (list, tuple):
             return max([max(l) for l in self.data])
         return max(self.data)
+
+    def getMin(self):
+        """Returns the minimum value of all datapoints. For list datatypes, this operation finds the smallest single
+        value in any list."""
+        if self.valueType in (list, tuple):
+            return min([min(l) for l in self.data])
+        return min(self.data)
 
 singleValueChannels = ['time', 'kn', 'pressure', 'force', 'volumeLoading', 'exitPressure', 'dThroat']
 multiValueChannels = ['mass', 'massFlow', 'massFlux', 'regression', 'web']
@@ -143,6 +150,20 @@ def getAveragePressure(self):
     def getMaxPressure(self):
         """Returns the highest chamber pressure that was observed during the motor's burn."""
         return self.channels['pressure'].getMax()
+
+    def getMinExitPressure(self):
+        """Returns the lowest exit pressure that was observed during the motor's burn, ignoring startup and shutdown transients"""
+        exit_pressures = self.channels['exitPressure'].getData()
+        return min(exit_pressures)
+
+    def getPercentBelowThreshold(self, channel, threshold):
+        """Returns the total number of seconds spent below a given threshold value"""
+        count = 0
+        data = self.channels[channel].getData()
+        for point in data:
+            if point < threshold:
+                count += 1
+        return count/len(data)
 
     def getImpulse(self, stop=None):
         """Returns the impulse the simulated motor produced. If 'stop' is set to a value other than None, only the

uilib/defaults.py

@@ -10,7 +10,9 @@
         'timestep': 0.03,
         'ambPressure': 101325,
         'igniterPressure': 150 * 6895, # Deprecated, but needed for migration
-        'mapDim': 750
+        'mapDim': 750,
+        'sepPressureRatio' : 0.4, # This is a good default value known as the Summerfield Criteria https://ntrs.nasa.gov/api/citations/19840011402/downloads/19840011402.pdf
+        'flowSeparationWarnPercent': 0.05
     },
     'units': {
         'm': 'in',

uilib/fileIO.py

@@ -9,7 +9,7 @@
 from .defaults import DEFAULT_PREFERENCES, DEFAULT_PROPELLANTS, KNSU_PROPS
 from .logger import logger
 
-appVersion = (0, 5, 0)
+appVersion = (0, 6, 0)
 appVersionStr = '.'.join(map(str, appVersion))
 
 class fileTypes(Enum):
@@ -66,6 +66,13 @@ def getConfigPath():
 
 def passthrough(data):
     return data
+
+
+#0.5.0 to 0.6.0
+def migrateMotor_0_5_0_to_0_6_0(data):
+    data['config']['sepPressureRatio'] = DEFAULT_PREFERENCES['general']['sepPressureRatio']
+    data['config']['flowSeparationWarnPercent'] = DEFAULT_PREFERENCES['general']['flowSeparationWarnPercent']
+    return data
 
 # 0.4.0 to 0.5.0
 
@@ -148,6 +155,12 @@ def migrateMotor_0_2_0_to_0_3_0(data):
     return data
 
 migrations = {
+    (0, 5, 0): {
+        'to': (0, 6, 0),
+        fileTypes.PREFERENCES: passthrough,
+        fileTypes.PROPELLANTS: passthrough,
+        fileTypes.MOTOR: migrateMotor_0_5_0_to_0_6_0
+    },
     (0, 4, 0): {
         'to': (0, 5, 0),
         fileTypes.PREFERENCES: migratePref_0_4_0_to_0_5_0,