How many extra stress terms occur due to the LES filtering operation?

How many extra stress terms occur due to the LES filtering operation? Correct Answer Three terms

The LES filtering operation resolves the flow variables into two – the filtered one and the unresolved spatial variations. This resolution leads to three extra stress terms. They are collectively called as Sub-Grid-Scale stresses.

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Which of the following filtering is done in frequency domain in correspondence to lowpass filtering in spatial domain?