Acts 10:3

He saw in a vision openly, as it were about the ninth hour of the day, an angel of God coming in unto him, and saying to him, Cornelius.

Although called a "vision," the addition of the word "openly" would seem to require that this supernatural event be understood as the actual appearance of an angel of God to Cornelius. Again from Hervey:

It was, as Meyer said, a clear angelic appearance. There was no indistinctness or confusion about it, and consequently it left no kind of doubt in the mind of Cornelius.[4]

Cornelius ... It is notable that the names of individuals are known by God and those representatives whom he commands to bear messages to men. Thus the angel called Cornelius by his name. Despite the fact of this man's worship and alms-giving, already mentioned, there is absolutely no evidence that he was a proselyte to Judaism. Hervey observed that:

He is spoken of simply as a Gentile and as uncircumcised, indicating that though he had learned from the Jews to worship the true God and to practice those virtues which went up as a memorial to God, yet he was in no sense a proselyte.[5]

An angel of God ... The Scriptures reveal no less than seven classes of functions performed by these holy beings on behalf of them who shall be saved, one of these being, as in evidence here, that of aiding providentially in bringing sinners into contact with the gospel. For more on this, see my Commentary on Hebrews and my Commentary on Luke.

[4] A. C. Hervey, op. cit., p. 333.

[5] Ibid.