ACR MLG FLC LOST ACFT CTL DUE TO CLR AIR TURB. ONE CABIN ATTENDANT INJURED.

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FOLLOWING A NORMAL DEP WE WERE CLRED TO FL290. DURING THE CLBOUT; WE ENCOUNTERED LIGHT TO OCCASIONAL MODERATE TURB; AS ANTICIPATED FROM PREFLT PAPERWORK AND ATC. AT FL290; 100 DME NW OF JVL VOR; WE EXPERIENCED AN ALT INCREASE AND DECREASE OF ABOUT 100 FT; SIMILAR TO A MOUNTAIN WAVE. AT ALT; THE SKY WAS VFR WITH JUST A WISP OF CLOUDS ABOUT WHERE THE MOUNTAIN WAVE OCCURRED. (NOTE: THERE SHOULDN'T HAVE BEEN A MOUNTAIN WAVE; AS WE WERE NOT NEAR ANY MOUNTAINS. WITHIN SECONDS OF THIS ALT EXCURSION; WE ENCOUNTERED SEVERE TURB WITH LOSS OF ACFT CTL. WE DSNDED; UNDER SOME CTL; TO FL210; WHERE SMOOTH AIR WAS ENCOUNTERED. DURING THE DSCNT; ONE GALLEY CART HIT THE CEILING OF THE ACFT; FLIPPED OVER; AND LANDED ON A FLT ATTENDANT; SPRAYING BEVERAGE AND BROKEN GLASS. ALL PAX WERE SEATED WITH SEATBELTS FASTENED. THE FLT ATTENDANT COMPLAINED OF BACK PAIN. NO PAX INJURY. I DON'T KNOW HOW TO FIX THIS PROB AS THERE MUST HAVE BEEN SOME UPPER AIR DISTURBANCE TO CAUSE THIS PROB. MY ONLY OBSERVATION OR 'HINT' THAT SOMETHING MIGHT BE UPCOMING WAS THE APPARENT 'MOUNTAIN WAVE' AND THE WISPY CLOUD IN THE OTHERWISE CLR SKY.