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This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic 'd-type' corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen-Kim k-[epsilon] turbulence model for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen-Kim k-[epsilon] and LVEL turbulence models show good agreement with the experimental measurements. [DOI: 10.1115/1.4002035] Keywords: numerical, experimental turbulent flow, 'd-type' corrugated pipes

Centrifugal pumps operate below their nominal capacity when handling gas-liquid flows. This problem is sensitive to many variables, such as the impeller speed and the liquid flow rate. Several works evaluate the effect of operating conditions in the pump performance, but few bring information about the associated gas-liquid flow dynamics. Studying the gas phase behavior, however, can help understanding why the pump performance is degraded depending on the operating condition. In this context, this paper presents a numerical and experimental study of the motion of bubbles in a centrifugal pump impeller. The casing and the impeller of a commercial pump were replaced by transparent components to allow evaluating the bubbles' trajectories through high-speed photography. The bubble motion was also evaluated with a numerical particle-tracking method. A good agreement between both approaches was found. The numerical model is explored to evaluate how the bubble trajectories are affected by variables such as the bubble diameter and the liquid flow rate. Results show that the displacement of bubbles in the impeller is hindered by an increase of their diameter and impeller speed but facilitated by an increase of the liquid flow rate. A force analysis to support understanding the pattern of the bubble trajectories was provided. This analysis should enlighten the readers about the dynamics leading to bubble coalescence inside an impeller channel, which is the main reason behind the performance degradation that pumps experience when operating with gas-liquid flows. [ABSTRACT FROM AUTHOR]

Centrifugal pumps operate below their nominal capacity when handling gas-liquid flows. This problem is sensitive to many variables, such as the impeller speed and the liquid flow rate. Several works evaluate the effect of operating conditions in the pump performance, but few bring information about the associated gas-liquid flow dynamics. Studying the gas phase behavior, however, can help understanding why the pump performance is degraded depending on the operating condition. In this context, this paper presents a numerical and experimental study of the motion of bubbles in a centrifugal pump impeller. The casing and the impeller of a commercial pump were replaced by transparent components to allow evaluating the bubbles' trajectories through high-speed photography. The bubble motion was also evaluated with a numerical particle-tracking method. A good agreement between both approaches was found. The numerical model is explored to evaluate how the bubble trajectories are affected by variables such as the bubble diameter and the liquid flow rate. Results show that the displacement of bubbles in the impeller is hindered by an increase of their diameter and impeller speed but facilitated by an increase of the liquid flow rate. A force analysis to support understanding the pattern of the bubble trajectories was provided. This analysis should enlighten the readers about the dynamics leading to bubble coalescence inside an impeller channel, which is the main reason behind the performance degradation that pumps experience when operating with gas-liquid flows. [ABSTRACT FROM AUTHOR]

This work presents an experimental analysis of gas--liquid flows in a centrifugal rotor prototype. Pressure rise curves are evaluated considering a wide range of liquid and gas flowrates and different rotating speeds. An innovative apparatus including a dynamic sealing system, back illumination, and filming in a rotating frame of reference is employed to visualize gas--liquid flow patterns at different operating conditions. Volume fraction measurement and bubble-size evaluation are also taken into account. The experimental apparatus allowed analyzing details of the gas-phase dynamics inside the rotor channels. That includes preferential bubble paths and zones of agglomeration, gas pocket formation, coalescence and breakup, and the effect of flow pattern transition on different degrees of performance degradation that centrifugal rotors are subject to when working with gas--liquid flows. Also, important information about the effect of the gas flowrate and the rotating speed on the performance of the assumed rotor prototype could be gathered. Discussions in this work should contribute to comprehend the behavior of gas--liquid flow in centrifugal pumps, a topic that is still far from being well understood. Qualitative and quantitative data here presented could also be valuable to guide the development of numerical models to solve this problem. [ABSTRACT FROM AUTHOR]