In the Fischer projection of glyceraldehyde, $\mathrm{CHO}$ is at the top, $\mathrm{CH}{}_2\mathrm{OH}$ at the bottom, and on the middle carbon OH is on the right and H on the left. The CIP descriptor and the D/L label are, respectively:

OH has the highest priority, then CHO, then $\mathrm{CH}{}_2\mathrm{OH}$, then H. H is on a horizontal bond, so the apparent sense OH to CHO to $\mathrm{CH}{}_2\mathrm{OH}$ (right, top, bottom) is anticlockwise and must be reversed, giving R. OH on the right gives the D label, so it is (R)-D-glyceraldehyde.