The function applies a Caesar cipher with a shift of 14 on each character, ignoring the case of the input.

[CODE]:

```python
def caesar_cipher(input_string, shift=14):
    result = ""
    for char in input_string:
        if char.isalpha():
            new_char = chr((((ord(char.lower()) - 97) + shift) % 26) + 97)
            result += new_char
        else:
            result += char
    return result
```