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Research Papers: Flows in Complex Systems

J. Fluids Eng. 2019;141(10):101101-101101-12. doi:10.1115/1.4043059.

The characteristics of radial pressure distribution inside side chamber and leakage flow through balancing holes of centrifugal pumps are very important for accurately predicting the axial thrust produced by a balancing system. Therefore, a rapid and sufficiently accurate calculation method is required. An integrated model describing the characteristics of radial pressure distribution inside side chamber and leakage flow rate through balancing holes was established. In this model, the correction coefficient of liquid pressure at side chamber entrance and the discharge coefficient of balancing holes were obtained by experiment. The IS 80-50-315 type single-suction, single-stage, and cantilevered centrifugal pump with the structure of double wear-rings and balancing holes was employed as a model to investigate the characteristics of internal liquid flow of the balancing system. Under different pump flow rates, pump performance curves, radial pressure distribution inside side chamber, and leakage flow rate through balancing holes were examined with different balancing hole diameters. Afterward, the experimental data were compared with the predicted results. The comparisons showed a reasonable consistency. Consequently, according to detailed pump dimensions and operating conditions, the integrated model in current form is recommended for centrifugal pumps, which have low specific speed and are with balancing systems of double wear-rings and balancing holes. This can be used for the prediction of radial pressure distribution inside side chamber and leakage flow rate through balancing holes and can be used both at the design stage and nondesign stage.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 2019;141(10):101102-101102-11. doi:10.1115/1.4043234.

While much is known on the effect of combustion chamber geometry on spray evolution in engines, less is known about its role in laboratory combustion chambers. This paper reports on a study, which investigates the effect of internal chamber geometry on the penetration and spreading angle of common rail nonreacting diesel sprays at room temperature conditions in a cylindrical constant volume chamber. This chamber has dimensions similar to those used in the literature. Spray chamber geometry was modified to yield three different chamber height-to-diameter ratios and two different nozzle stand-off distances. Sprays from three nozzles, two single-hole nozzles with different diameter and one twin-hole nozzle (THN), were examined for two injection pressures of 100 MPa and 150 MPa into two chamber pressures of 0.1 MPa and 5 MPa. To characterize the spray structure, a volume illumination method was used to study the spray tip penetration/speed and spread angle. For both injection pressures used with chamber pressure of 5 MPa, little sensitivity to vessel geometry was found in penetration distance and tip speed for variation in height to diameter ratio from 0.6 to 2.6 and variation in nozzle stand-off distance from 2 mm to 54 mm. For atmospheric chamber pressure, sensitivity to chamber geometry was evident and found to vary with nozzle type. Spread angle was found more largely affected by the calculation method and very sensitive to the image intensity threshold value for the cases investigated.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 2019;141(10):101103-101103-9. doi:10.1115/1.4043235.

This paper presents an improved method of time-domain modeling of pressure wave propagation through liquid media in rigid tapered pipes. The method is based on the transmission line model (TLM), which uses linear transfer functions and delays to calculate the pressures and/or flows at the pipe inlet and outlet. This method is computationally efficient and allows for variable rate simulation. The proposed form of the model differs from previous TLM models in the literature, allowing it to accurately model both low and high frequency characteristics.

Commentary by Dr. Valentin Fuster

Research Papers: Fundamental Issues and Canonical Flows

J. Fluids Eng. 2019;141(10):101201-101201-9. doi:10.1115/1.4043061.

A Bernoulli pad uses an axial jet to produce radial outflow between the pad and a proximally located parallel surface. The flow field produces a force between the surfaces, which depends upon their spacing h. The direction of this force is repulsive as h approaches zero and becomes attractive as h increases. This yields a stable equilibrium point heq, where the force is equal to zero. The present computational work indicates that a power-law relationship exists between heq and the inlet fluid power required to sustain this equilibrium spacing when each is appropriately scaled. This scaling is derived principally from the wall shear; an additional term incorporating the inlet Reynolds number is used to account for the force applied to the system. The relationship is valid over a range of forces acting on the system, geometric, and material properties.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 2019;141(10):101202-101202-11. doi:10.1115/1.4043162.

The affinity law modified for viscosity effects is further extended to include the power input and efficiency. The power input and efficiency data generated using computational fluid dynamics (CFD) are utilized to represent dimensionless power coefficient and efficiency for the pump under consideration. The goal of modifying the affinity laws for power input is achieved by developing a new relationship where the power coefficient is modified by multiplying it by rotational Reynolds number raised to a power Π*RewPat. This new relationship is then represented as a function of a modified flow coefficient ф*RewMo. All the data collapse onto a single curve for varying values of the exponents Morrison number (Mo) and Patil number (Pat). Pat is further characterized as a function of flow regime and specific speed. The method also holds true for efficiency prediction, however, with different values of Mo and Pat. The proposed method is validated by using data collected from published literature.

Commentary by Dr. Valentin Fuster

Research Papers: Multiphase Flows

J. Fluids Eng. 2019;141(10):101301-101301-9. doi:10.1115/1.4043233.

Flow dynamics in a pipe with an abrupt change in diameter was experimentally and numerically analyzed. Two-dimensional stationary Reynolds-averaged Navier–Stokes (RANS) k–ε epsilon model was used to describe the development of axial and radial velocity and turbulent kinetic energy in two cases. The theoretical results were compared with experimental findings gained in a transparent pipe test rig. Particle image velocimetry (PIV) technique was used to analyze the development of flow in a pipe with complex geometry. The measured and modeled velocities and turbulent kinetic energy were found to be in good agreement. The two-dimensional stationary RANS k–ε model is suitable for the analysis of the flow dynamics in real old rough pipes where the pipe wall build-up leads to changes in the actual diameter of the pipe but the flow can still be considered axially symmetrical.

Commentary by Dr. Valentin Fuster

Research Papers: Techniques and Procedures

J. Fluids Eng. 2019;141(10):101401-101401-22. doi:10.1115/1.4043168.

Grid fins are unconventional control surfaces consisting of an outer frame supporting an inner grid of intersecting planar surfaces. Although afflicted with higher drag, these have been credited for their enhanced lifting characteristics at high angles of attack and high Mach numbers, alongside reduced hinge moments accounting for the recent upsurge in their usage on numerous aerospace applications. Present investigations carry out elaborate flow field visualization and characterization underlining the rudimentary physics through a sequence of subsonic numerical simulations performed at different angles of attack and different gap (between the members) to chord ratios on a simplified grid fin variant called cascade fin. The study makes use of a new nondimensionalization technique called cumulative nondimensionalization to decipher the effect of cascading on individual members of the fin. Hence, after a comprehensive examination of the aerodynamic coefficients, pressure coefficient distribution, pressure gradient, velocity gradient, boundary layer velocity profile, and flow field visualization, the study elucidates physics associated with hastened stall angle, augmented lift-drag, and bounded efficiency accretion for gap increment.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Fluids Eng. 2019;141(10):104501-104501-8. doi:10.1115/1.4043232.

Many uncertain factors in the water-emerging process of a vehicle influence the taking effect of the air film around its shoulder in the load reduction and attitude control. Assuming the launch parameters (launch depth, vehicle velocity, and chamber pressure) as sources of uncertainties, the uncertain evolution process of the air film in the water-emerging process of a vehicle is quantified by adopting the nonintrusive polynomial chaos (NIPC) method with the sample space constructed using linearly independent probabilistic collocation points. A sensitivity analysis was conducted for the key performance indicators of the air film to evaluate the contribution of each uncertain launch parameter.

Commentary by Dr. Valentin Fuster

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