convert temperature to Celcius and use 'r' as diameter not radius

opendrift/models/openoil/openoil.py

@@ -854,7 +854,9 @@ def update_terminal_velocity(self,
                 weight_upper + \
                 Sprofiles[lower, range(Sprofiles.shape[1])] * \
                 (1-weight_upper)
-
+
+        T0 = T0 - 273.15 # convert to Celcius - needed for the calcs in this method
+
         rho_oil = self.elements.density
         rho_water = self.sea_water_density(T=T0, S=S0)
 
@@ -868,10 +870,10 @@ def update_terminal_velocity(self,
 
         # terminal velocity for low Reynolds numbers
         kw = 2 * g * (1 - rhopr) / (9 * ny_w)
-        W = kw * r**2
+        W = kw * (r/2)**2 # r is diameter so divide by 2 for radius
 
         # check if we are in a high Reynolds number regime
-        Re = 2 * r * W / ny_w
+        Re = r * W / ny_w # r is diameter so no need to multiply by 2
         highRe = np.where(Re > 50)
 
         # Terminal velocity in high Reynolds numbers