There is no default username and password created if you are just using python wheel.
Run the following to create a user:
For Airflow >=2.0.0:
airflow users create --role Admin --username admin --email admin --firstname admin --lastname admin --password admin
OR
For Airflow <1.10.14:
airflow create_user -r Admin -u admin -e [email protected] -f admin -l user -p admin