According to Trinitarians, when the term Yahweh ('LORD') is used in the OT, who exactly is being referred to?

According to Unitarian Christians, the identity of Yahweh is straightforward. Yahweh = the Father = God. Therefore, linguistic usage in the OT is fairly straightforward. Whenever Yahweh ('LORD') is mentioned, it is the Father. For Trinitarians, when Yahweh is used in the OT, what does it mean? Is it God inclusive of the 3 persons of the Trinity? Or does it mean the Father? The Son? Or, like the word 'God' in the New Testament according to Trinitarians, does the meaning of Yahweh in the OT change depending on context?