The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform

Michael T. Montgomery - One of the best experts on this subject based on the ideXlab platform.

  • Sensitivity of tropical‐cyclone intensification to perturbations in the surface Drag Coefficient
    Quarterly Journal of the Royal Meteorological Society, 2012
    Co-Authors: Gerald L. Thomsen, Michael T. Montgomery, Roger K. Smith
    Abstract:

    The recent studies of the sensitivity of tropical-cyclone intensification to the surface Drag Coefficient in a three-dimensional model by Montgomery et al., and Smith et al., are extended to include perturbations of the surface Drag Coefficient in one of four boundary-layer parametrization schemes: the bulk scheme, the Blackadar scheme, the MRF scheme, and the Gayno–Seaman scheme. The schemes are slightly modified to have the same Drag Coefficient formulation and the same constant exchange Coefficients for sensible heat and moisture. We find that the intensification rate and mature intensity are essentially unaltered when the Drag Coefficient is perturbed randomly by variations of up to 60%. The results, in conjunction with an analysis of coherent Drag Coefficient variations for a moving vortex, question the notion that coupled wind–wave mod els are necessary to accurately forecast tropical-cyclone intensification and mature intensity.

  • sensitivity of tropical cyclone models to the surface Drag Coefficient
    Quarterly Journal of the Royal Meteorological Society, 2010
    Co-Authors: Michael T. Montgomery, Roger K. Smith, Sang V Nguyen
    Abstract:

    Motivated by recent developments in tropical-cyclone dynamics, this paper reexamines a basic aspect of tropical-cyclone behaviour, namely, the sensitivity of tropical-cyclone models to the surface Drag Coefficient. Previous theoretical and numerical studies of the sensitivity in axisymmetric models have found that the intensity decreases markedly with increasing Drag Coefficient. Here we present a series of three-dimensional convection-permitting numerical experiments in which the intensification rate and intensity of the vortex increase with increasing surface Drag Coefficient until a certain threshold value is attained and then decrease. In particular, tropical depression-strength vortices intensify to major hurricane intensity for values of CK/CD as small as 0.1, significantly smaller than the critical threshold value of about 0.75 for major hurricane development predicted by Emanuel using an axisymmetric balance model. Moreover, when the Drag Coefficient is set to zero, no system-scale intensification occurs, despite persistent sea-to-air fluxes of moisture that maintain deep convective activity. This result is opposite to that found in a prior axisymmetric study by Craig and Gray. The findings are interpreted using recent insights obtained on tropical-cyclone intensification, which highlight the intrinsically unbalanced dynamics of the tropicalcyclone boundary layer. The reasons for the differences from earlier axisymmetric studies and some potential ramifications of our findings are discussed. The relative insensitivity of the intensification rate and intensity found for Drag Coefficients typical of high wind speeds over the ocean calls into question the need for coupled ocean wave–atmospheric models to accurately forecast tropical-cyclone intensity. Copyright c � 2010 Royal Meteorological Society

Yijun Cao - One of the best experts on this subject based on the ideXlab platform.

  • Drag Coefficient Prediction of a Single Bubble Rising in Liquids
    Industrial & Engineering Chemistry Research, 2018
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao, Kaixin Zheng, Miao Zhenyong, Jiongtian Liu
    Abstract:

    The motion of single bubbles rising in 2-octanol solutions was investigated experimentally. By using a high-speed video system to follow the rising bubble, the sequences of the recorded frames were digitized and analyzed using image analysis software. The periodical fluctuation of the bubble terminal velocity was observed, which is indicative of a nonconstant bubble Drag Coefficient. Then, the measured Drag Coefficient was compared with correlations available in the literature. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Using the extensive experimental data, the authors proposed a new correlation to predict the Drag Coefficient calculated from the fluctuated motion with the added mass force and history force included. In virtue of nonlinear curve fitting, the Drag Coefficient of the single bubble is correlated as a function of the Re number, Eo number, We number, and Mo number based on the equivalent bubble diameter. T...

  • Drag Coefficient fluctuation prediction of a single bubble rising in water
    Chemical Engineering Journal, 2017
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao
    Abstract:

    Abstract The Drag Coefficient has a significant effect on the calculation of bubble motion. This paper experimentally investigated the Drag Coefficient of a single bubble rising in deionized water with the help of a high-speed video system. First, it is found that the terminal velocity presented periodical fluctuation, indicating that the Drag Coefficient is not a constant value. Then the measured Drag Coefficient was compared with correlations available in literatures. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Based on massive data analysis, a new correlation combined Reynolds number, Eotvos number and Weber number was proposed to calculate the fluctuation of Drag Coefficient. The Drag Coefficient predicted by this new model is in excellent agreement with the experimental results over the range of 550 ⩽ Re ⩽ 1700, and the largest relative error is less than 0.4%. Comparing with data of water from existing literature under the condition of 8

Yan Jia - One of the best experts on this subject based on the ideXlab platform.

  • Drag Coefficient Prediction of a Single Bubble Rising in Liquids
    Industrial & Engineering Chemistry Research, 2018
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao, Kaixin Zheng, Miao Zhenyong, Jiongtian Liu
    Abstract:

    The motion of single bubbles rising in 2-octanol solutions was investigated experimentally. By using a high-speed video system to follow the rising bubble, the sequences of the recorded frames were digitized and analyzed using image analysis software. The periodical fluctuation of the bubble terminal velocity was observed, which is indicative of a nonconstant bubble Drag Coefficient. Then, the measured Drag Coefficient was compared with correlations available in the literature. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Using the extensive experimental data, the authors proposed a new correlation to predict the Drag Coefficient calculated from the fluctuated motion with the added mass force and history force included. In virtue of nonlinear curve fitting, the Drag Coefficient of the single bubble is correlated as a function of the Re number, Eo number, We number, and Mo number based on the equivalent bubble diameter. T...

  • Drag Coefficient fluctuation prediction of a single bubble rising in water
    Chemical Engineering Journal, 2017
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao
    Abstract:

    Abstract The Drag Coefficient has a significant effect on the calculation of bubble motion. This paper experimentally investigated the Drag Coefficient of a single bubble rising in deionized water with the help of a high-speed video system. First, it is found that the terminal velocity presented periodical fluctuation, indicating that the Drag Coefficient is not a constant value. Then the measured Drag Coefficient was compared with correlations available in literatures. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Based on massive data analysis, a new correlation combined Reynolds number, Eotvos number and Weber number was proposed to calculate the fluctuation of Drag Coefficient. The Drag Coefficient predicted by this new model is in excellent agreement with the experimental results over the range of 550 ⩽ Re ⩽ 1700, and the largest relative error is less than 0.4%. Comparing with data of water from existing literature under the condition of 8

Xiaokang Yan - One of the best experts on this subject based on the ideXlab platform.

  • Drag Coefficient Prediction of a Single Bubble Rising in Liquids
    Industrial & Engineering Chemistry Research, 2018
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao, Kaixin Zheng, Miao Zhenyong, Jiongtian Liu
    Abstract:

    The motion of single bubbles rising in 2-octanol solutions was investigated experimentally. By using a high-speed video system to follow the rising bubble, the sequences of the recorded frames were digitized and analyzed using image analysis software. The periodical fluctuation of the bubble terminal velocity was observed, which is indicative of a nonconstant bubble Drag Coefficient. Then, the measured Drag Coefficient was compared with correlations available in the literature. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Using the extensive experimental data, the authors proposed a new correlation to predict the Drag Coefficient calculated from the fluctuated motion with the added mass force and history force included. In virtue of nonlinear curve fitting, the Drag Coefficient of the single bubble is correlated as a function of the Re number, Eo number, We number, and Mo number based on the equivalent bubble diameter. T...

  • Drag Coefficient fluctuation prediction of a single bubble rising in water
    Chemical Engineering Journal, 2017
    Co-Authors: Xiaokang Yan, Yan Jia, Lijun Wang, Yijun Cao
    Abstract:

    Abstract The Drag Coefficient has a significant effect on the calculation of bubble motion. This paper experimentally investigated the Drag Coefficient of a single bubble rising in deionized water with the help of a high-speed video system. First, it is found that the terminal velocity presented periodical fluctuation, indicating that the Drag Coefficient is not a constant value. Then the measured Drag Coefficient was compared with correlations available in literatures. The comparison shows that these correlations cannot give fully satisfactory results in predicting the fluctuated Drag Coefficient. Based on massive data analysis, a new correlation combined Reynolds number, Eotvos number and Weber number was proposed to calculate the fluctuation of Drag Coefficient. The Drag Coefficient predicted by this new model is in excellent agreement with the experimental results over the range of 550 ⩽ Re ⩽ 1700, and the largest relative error is less than 0.4%. Comparing with data of water from existing literature under the condition of 8

Roger K. Smith - One of the best experts on this subject based on the ideXlab platform.

  • Sensitivity of tropical‐cyclone intensification to perturbations in the surface Drag Coefficient
    Quarterly Journal of the Royal Meteorological Society, 2012
    Co-Authors: Gerald L. Thomsen, Michael T. Montgomery, Roger K. Smith
    Abstract:

    The recent studies of the sensitivity of tropical-cyclone intensification to the surface Drag Coefficient in a three-dimensional model by Montgomery et al., and Smith et al., are extended to include perturbations of the surface Drag Coefficient in one of four boundary-layer parametrization schemes: the bulk scheme, the Blackadar scheme, the MRF scheme, and the Gayno–Seaman scheme. The schemes are slightly modified to have the same Drag Coefficient formulation and the same constant exchange Coefficients for sensible heat and moisture. We find that the intensification rate and mature intensity are essentially unaltered when the Drag Coefficient is perturbed randomly by variations of up to 60%. The results, in conjunction with an analysis of coherent Drag Coefficient variations for a moving vortex, question the notion that coupled wind–wave mod els are necessary to accurately forecast tropical-cyclone intensification and mature intensity.

  • sensitivity of tropical cyclone models to the surface Drag Coefficient
    Quarterly Journal of the Royal Meteorological Society, 2010
    Co-Authors: Michael T. Montgomery, Roger K. Smith, Sang V Nguyen
    Abstract:

    Motivated by recent developments in tropical-cyclone dynamics, this paper reexamines a basic aspect of tropical-cyclone behaviour, namely, the sensitivity of tropical-cyclone models to the surface Drag Coefficient. Previous theoretical and numerical studies of the sensitivity in axisymmetric models have found that the intensity decreases markedly with increasing Drag Coefficient. Here we present a series of three-dimensional convection-permitting numerical experiments in which the intensification rate and intensity of the vortex increase with increasing surface Drag Coefficient until a certain threshold value is attained and then decrease. In particular, tropical depression-strength vortices intensify to major hurricane intensity for values of CK/CD as small as 0.1, significantly smaller than the critical threshold value of about 0.75 for major hurricane development predicted by Emanuel using an axisymmetric balance model. Moreover, when the Drag Coefficient is set to zero, no system-scale intensification occurs, despite persistent sea-to-air fluxes of moisture that maintain deep convective activity. This result is opposite to that found in a prior axisymmetric study by Craig and Gray. The findings are interpreted using recent insights obtained on tropical-cyclone intensification, which highlight the intrinsically unbalanced dynamics of the tropicalcyclone boundary layer. The reasons for the differences from earlier axisymmetric studies and some potential ramifications of our findings are discussed. The relative insensitivity of the intensification rate and intensity found for Drag Coefficients typical of high wind speeds over the ocean calls into question the need for coupled ocean wave–atmospheric models to accurately forecast tropical-cyclone intensity. Copyright c � 2010 Royal Meteorological Society