Is the DES algorithm in OPENSSL random?
Using the -k option, you can specify a password. Passwords are not really encryption keys, so OpenSSL uses a key derivation process to turn the password into an encryption key. It turns out by default OpenSSL uses a salt in that derivation process (which is why you see Salted__ in the output, which is a magic to indicate that the next 8 bytes are the randomly generated salt). The ciphertext only starts from byte 16 onwards.

If the salt changes, the encryption key changes. If the encryption key changes, the ciphertext changes. By default OpenSSL generates a new random salt every execution. That is why you are seeing the changing ciphertext.

To turn this off you can add -nosalt. This is fine for testing purposes. As stated in the OpenSSL docs "This option SHOULD NOT be used except for test purposes or compatibility with ancient versions of OpenSSL and SSLeay". Otherwise your ciphertext is deterministic which can lead to cryptanalysis and a broken (i.e., insecure) system.

Alternatively -K lets you directly specify a key value in hexadecimals, skipping the (OpenSSL specific) password key derivation - and therefore the salt generation - entirely. You also need to specify the IV using -iv in that case. The IV should be random to achieve security in CBC mode if the key is reused, but the generation of the IV is left to the user.