Research within organisations
In the US, if you are conducting a survey or certain type of interview, you need to have it approved (or declared exempt) by your campus IRB committee. This body will regulate what you need to disclose, and will also approve the wording of any cover letter.

In a written context, putting the cover letter on school letterhead should convey that the project is academic.

In an interview, you would likely state that you are a PhD student at UNIVERSITY and are working on a dissertation related to X to convey that your project is an academic one.