code: public static String DEFAULT_FLOW_DIR() {
      String flow_dir = null;
  
      try {
        if (ARGS.ga_hadoop_ver != null) {
          PersistManager pm = getPM();
          if (pm != null) {
            String s = pm.getHdfsHomeDirectory();
            if (pm.exists(s)) {
              flow_dir = s;
            }
          }
          if (flow_dir != null) {
            flow_dir = flow_dir + "/h2oflows";
          }
        } else {
          flow_dir = System.getProperty("user.home") + File.separator + "h2oflows";
        }
      }
      catch (Exception ignore) {
        // Never want this to fail, as it will kill program startup.
        // Returning null is fine if it fails for whatever reason.
      }
  
      return flow_dir;
    }
docs: Place to store flows