Just check first which filenames already exist using os.path.isfile(filename):
import os
n=1
while True:
fname=str(n)+'.csv'
if os.path.isfile(fname):
#file exists, append counter
n=n+1
else:
#file not found, exit loop
break
print(fname) #here...
The problem is that the TEMP field output contains values at element integration points and you are trying to extract a nodal subset from it. Use either fieldOutputs['NT11'] or extrapolate the integration point values to nodes using getSubset(region=resultsSet, position=ELEMENT_NODAL).
