報告書番号

U89047

タイトル（和文）

温排水の水中放流による局所洗掘現象の予測手法の開発

タイトル（英文）

NUMERICAL PREDICTION METHOD FOR LOCAL SCORING BY COOLING WATER DISCHARGED FROM SUBMERGED OUTLETS

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では，温排水の水中放流による局所洗掘現象を予測するための数値解析手法を開発した。この解析手法では，局所洗掘による時間とともに変形する計算領域内で，温排水の移流拡散過程を２方程式乱流モデルで計算し，その掃流力から掃流砂量と浮遊砂量を算出して砂面の変形過程を計算する。計算においては，これら２つの過程の相互作用が考慮されている。実験結果との比較により本解析手法の適用性の検討を行った結果，次のことが明らかとなった。固定床上における温排水の流速の３次元的な分布は，適切に計算された。また，２次元局所洗掘実験の結果との比較から，各時刻の砂面の変形過程や流速分布は数値解析によりほぼ適切に計算された。また，３次元局所洗掘実験へ本解析法を適用した結果，最大洗掘深の発生箇所にやや相違があるものの，その値はほぼ正しく計算された。

概要 （英文）

THIS PAPER DESCRIBES THE INVESTIGATION OF A NUMERICAL PREDICTION METHOD FOR LOCAL SCORING OF A SAND BED CAUSED BY WARM COOLING WATER DISCHARGED FROM THE OUTLETS OF ELECTRIC-POWER PLANTS.THE PREDICTION METHOD DEALS WITH TWO INTERACTIVE PROCESSES: THE CONVECTION AND DIFFUSION PROCESS OF THE DISCHARGED WARM WATER,AND THE LOCAL SCORING PROCESS. THE FORMER PROCESS IS CALCULATED WITH A TWO-EQUATION TURBULENCE MODEL FOR THE AREA DEFORMED BY THE LOCAL SCORING WITH TIME. THE LATTER PROCESS WAS EVALUATED BY THE BED LOAD AMOUNT AND THE SUSPENSION LOAD TRANSPORTED BY THE TRACTIVE FORCE OF THE CALCULATEDFLOW. THESE PROCESSES ARE SIMULATED ALMOST SIMULTANEOUSLY SO THEIR MUTUAL INTERACTION IS CONSIDERED. THE VALIDITY OF THE PREDICTION METHOD WAS PROVED BY COMPARISON WITH EXPERIMENTAL RESULTS. THREE-DIMENSIONAL CALCULATIONS WERECARRIED OUT FOR COOLING WATER DISCHARGE TESTS ON A STATIONARY BED. THEHORIZONTAL AND VERTICAL DISTRIBURIONS OF THE STREAMWISE VELOCITY WERE CORRECTLY PREDICTED. MEASUREMENTS OF THE SHAPES OF THE SAND BED AND VELOCITY DISTRIBUTIONS WERE MADE FOR TWO-DIMENSIONAL LOCAL-SCORING EXPERIMENTS. THE SIMULATED DEPTH AND SHAPE OF THE SCORED SAND BED EACH TIME AND THE VELOCITY DISTRIBUTIONS ABOVE THE BED ALMOST AGREED WITH THE EXPERIMENTAL VALUES. FOR THE TWO-DIMENSIONAL SHAPES OF A SCORED BED IN THREE-DIMENSIONAL LOCAL-SCORING EXPERIMENTS,ALTHOUGH THE AREAS WHERE THE CALCULATED MAXIMUM DEPTH OCCURRD TENDED TO BE NEARER THE CENTER LINE AND FARTHER FROM THE OUTLETS THAN THE EXPERIMENTAL RESULTS THE DEPTH WAS SIMULATED ALMOST CORRECTLY.

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