If you can define a closed path in your data over which to integrate, you can calculate circulation using the Analyze/Perform Integration menu option. In the Integrate dialog, for Type of Integration, select Vector Dotted with Unit Tangential, and select your velocity components for the Integrand. You then need to identify a line--a closed path--as your Domain of Integration. If you want to read more on specifying the domain of integration, click the Help button and scroll down a bit on the resulting help Web page. Click Integrate when you are done, and the circulation will be displayed as the integration result.