Accepted Manuscripts

Eduard Ron and Kam Chana
J. Fluids Eng   doi: 10.1115/1.4037140
This paper expands on the numerical simulation of entropy noise by performing a comparison of two commonly used models for resolving turbulent flow field: Large Eddy Simulation and Unsteady Reynolds Averaged Navier-Stokes. A brand new numerical procedure was developed allowing an accurate reproduction of two-dimensional spatial and temporal temperature variations of a non-uniform temperature profile. Experimental investigation was performed for the same non-uniform temperature profile, and comparison of the entropy noise level measured experimentally and evaluated numerically using the two models was performed. It was shown that Large Eddy Simulation allows a better prediction of entropy noise within the developed numerical procedure than Unsteady Reynolds Averaged Navier-Stokes.
TOPICS: Entropy, Noise (Sound), Large eddy simulation, Temperature profiles, Temperature, Turbulence, Computer simulation
David S. Adebayo and Aldo Rona
J. Fluids Eng   doi: 10.1115/1.4037083
An investigation is conducted on the flow in a moderately wide gap between an inner rotating shaft and an outer coaxial fixed tube, with stationary end-walls, by three dimensional Reynolds Averaged Navier-Stokes (RANS) Computational Fluid Dynamics, using the realizable k-epsilon model. This approach provides three-dimensional spatial distributions of static and of dynamic pressure that are not directly measurable in experiment by conventional non-intrusive optics-based techniques. The non-uniform pressure main features on the axial and meridional planes appear to be driven by the radial momentum equilibrium of the flow, which is characterised by axisymmetric Taylor vortices over the Taylor number range 2.35 × 10^6 <= Ta <= 6.47 × 10^6. Regularly spaced static and dynamic pressure maxima on the stationary cylinder wall follow the axial stacking of the Taylor vortices and line up with the vortex induced radial outflow documented in previous work. This new detailed understanding has potential for application to the design of a vertical turbine pump head. Aligning the location where the gauge static pressure maximum occurs with the central axis of the delivery pipe could improve the head delivery, the pump mechanical efficiency, the system operation, and control costs.
TOPICS: Flow (Dynamics), Pressure, Vortices, Pumps, Turbines, Momentum, Optics, Gages, Equilibrium (Physics), Computational fluid dynamics, Design, Pipes, Cylinders, Reynolds-averaged Navier–Stokes equations, Outflow, Mechanical efficiency
Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush and Esteve Codina Macia
J. Fluids Eng   doi: 10.1115/1.4037060
A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On one hand, a contact point viscosity model is used for the simulation of solid-solid contact between gears, in order to avoid the teeth tip leakage. On the other hand a new boundary condition for the gear mesh points motion has been implemented in order to keep the mesh quality while moving gears with relative velocity. The results have been compared with experimental measurement and a good agreement in volumetric efficiency and pressure fluctuations have been found. Finally the leakage flow in the clearance disk has been analyzed.
TOPICS: Fluid dynamics, Simulation, Pumps, Gears, Clearances (Engineering), Pressure, Computer simulation, Disks, Leakage, Boundary-value problems, Leakage flows, Viscosity, Fluctuations (Physics)
Prashant Kumar and Frederic Topin
J. Fluids Eng   doi: 10.1115/1.4037034
Foam structures are a class of modern micro-porous media that possesses high thermal conductivity, large accessible specific surface area and high porosities. Nowadays, industrial applications such as filtration, heat exchange and chemical reaction, etc. utilize porous media such as open-cell foams. Knowledge of pressure drop induced by these foam matrices is essential for successful design and operation of high performance industrial systems. The homogenized pressure drop data in the literature are widely dispersed (up to two-orders of magnitude) despite numerous researches has been conducted since two decades. Most of the empirical pressure drop correlations were derived using Ergun-like approach. In this view, a careful evaluation of empirical correlations as well as the relationship of intrinsic flow law characteristics (permeability and inertia coefficient) with morphological parameters is imperative. This paper presents the start-of-the-art of various pressure drop correlations as well as highlights the ambiguities and inconsistencies in various definitions of several key parameters. The applicability of the empirical correlations presented in the literature was examined by comparing them against numerically calculated pressure drop data of open-cell foams (metal and ceramic) for the porosities ranging from 0.60 up to 0.95. A comprehensive study has been conducted to identify the reasons of dispersed pressure drop data in the literature. Although, substantial progress has been made in the field of fluid flow in open-cell foams, it is yet difficult to predict pressure drop data from a given set of morphological parameters.
TOPICS: Foams (Chemistry), Pressure drop, Ambiguity, Chemical reactions, Metals, Porous materials, Filtration, Ceramics, Thermal conductivity, Design, Inertia (Mechanics), Fluid dynamics, Flow (Dynamics), Heat, Permeability
Luke S Roberts, Mark V Finnis and Kevin Knowles
J. Fluids Eng   doi: 10.1115/1.4037036
The transition from a laminar to turbulent boundary layer on a wing operating at low Reynolds numbers can have a large effect on its aerodynamic performance. For a wing operating in ground effect, where very low pressures and large pressure gradients are common, the effect is even greater. A study was conducted into the effect of forcing boundary-layer transition on the suction surface of an inverted GA(W)-1 section single-element wing in ground effect, which is representative of a racing-car front wing. Transition to a turbulent boundary layer was forced at varying chordwise locations and compared to the free-transition case using experimental and computational methods. Forcing transition caused the laminar separation bubble, which was the unforced transition mechanism, to be eliminated in all cases and trailing-edge separation to occur instead. The aerodynamic forces produced by the wing with trailing-edge separation were shown to be dependent on trip location. As the trip was moved upstream the separation point also moved upstream, this led to an increase in drag and reduction in downforce. In addition to significant changes to the pressure field around the wing, turbulent energy in the wake was considerably reduced by forcing transition. The differences between free- and forced-transition wings were shown to be significant, highlighting the importance of modelling transition for ground-effect wings. Additionally, it has been shown that whilst it is possible to reproduce the force coefficient of a higher Reynolds number case by forcing the boundary layer to a turbulent state, the flow features, both on-surface and off-surface, are not recreated.
TOPICS: Boundary layers, Wings, Separation (Technology), Turbulence, Reynolds number, Boundary layer turbulence, Pressure gradient, Computational methods, Modeling, Pressure, Flow (Dynamics), Aerodynamics, Wakes, Bubbles, Fluid-dynamic forces, Suction, Drag (Fluid dynamics)
Lance W. Traub
J. Fluids Eng   doi: 10.1115/1.4037037
A low speed wind tunnel investigation is presented characterizing the impact of Gurney flaps on an elliptical airfoil. The chordwise attachment location and height of the flaps were varied, as was the Reynolds number. The results showed strong non-linearities in the lift curve which were present for all tested geometries. Flap effectiveness was seen to diminish as the flap was moved closer to the trailing edge stemming from flap submersion in separated flow. For the tested cases, the measured lift coefficients showed a weak Re dependency. The upper airfoil surface was shown to carry approximately 80% of the total lift load. The top surface caused a pitching moment reversal associated with non-linearity in the lift curve.
TOPICS: Airfoils, Flow (Dynamics), Reynolds number, Stress, Wind tunnels
Hans-Arndt Freudigmann, Uwe Iben, Aaron Dörr and Peter F. Pelz
J. Fluids Eng   doi: 10.1115/1.4037048
Impurities like air bubbles in hydraulic liquids can significantly affect the performance and reliability of hydraulic systems. The aim of this study was to develop a model suited for hydraulic system simulation to determine the rate of degassing of dissolved air in a micro-orifice flow at cavitating conditions. An existing model for the flow through a micro-orifice was extended to account for the generation of vapor which is suggested to play the key-role for the degassing mechanism. In comparison with measurements, the results of the modeling approach imply that diffusive mass transfer of dissolved air into generated vapor cavities is the dominating mechanism for the observed air release phenomena.
TOPICS: Flow (Dynamics), Cavitation, Modeling, Vapors, Hydraulic drive systems, Reliability, Simulation, Mass transfer, Cavities, Bubbles
Derek B. Ancrum and Metin I. Yaras
J. Fluids Eng   doi: 10.1115/1.4037044
This study presents experimental results on the effects of riblets on the coherent structures of turbulence within a turbulent spot developing under favourable pressure gradients. The riblet spacings of the study correspond to 0.5 and 1.5 times the natural spacing of the low-speed streak. The cross-sectional dimensions of the riblets were chosen to control the spatial distribution of wave packets consisting of streamwise-aligned hairpin vortices. Both riblet spacings demonstrated effective control on the spanwise positioning of the wave packets. The wider spaced riblets reduced spanwise mutual interaction between wave packets. The closer-spaced riblets promoted this interaction via spanwise-oriented vortical structures which produced stronger turbulent fluctuations.
TOPICS: Turbulence, Dimensions, Fluctuations (Physics), Wave packets, Vortices, Boundary layer turbulence, Pressure gradient
Patrick Fillingham, Harikrishnan Murali and Igor Novosselov
J. Fluids Eng   doi: 10.1115/1.4037035
Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field resulting from normally impinging axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle while varying the height to diameter ratio (H/D) and the inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. A Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP<1), (ii) transitional (12). It is observed that wall shear stress is limited to a finite value due to jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime. Additionally, the formation of shock structures in the wall flow were observed for DJP>2, resulting in difficulties with dimensionless analysis. In subsonic impingement and transitional regimes, equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships, wall shear stress can be predicted at all locations along the impingement surface.
TOPICS: Jets, Shear stress, Flow (Dynamics), Shock (Mechanics), Computational fluid dynamics, Energy dissipation, Nozzles, Schlieren methods, Particulate matter, Density, Pressure
Shiyang Hou, Jibin Hu and Peng Zengxiong
J. Fluids Eng   doi: 10.1115/1.4037055
The drag torque caused by the viscous shear in open multi-plates wet clutches has been studied in most available literature whose focus is placed on low circumferential speed. However, the drag torque increases drastically in the high circumferential speed range. The underlying physical principles and the influencing factors of the drag torque at high speed are still indeterminate. The present study aims to experimentally investigate the characteristics of the wobbling vibrations of plates and to characterize the effects of average clearance, flow rate of lubricant, shifting condition, and the number of friction interfaces on the drag torque at high circumferential speed. The result of the experiment reveals that the friction plate starts to wobble periodically at low circumferential speed, though the effect is insignificant. The dominant frequency of plate wobbling movements increases with the input speed. When wobbling vibrations of plates become unstable, the wobble gradually becomes nonlinear. The experiments confirm that the mechanical contacts between plates during the unstable wobbling vibration result in the drag torque rise at high circumferential speed. At high speed, the supplying flow rate of the lubricant influences the drag torque values. The rotation of separator plates brings forward the torque rise and makes the drag torque rise smoother. By reducing the number of interfaces, the drag torque rise is delayed and the magnitude becomes smaller. Finally, a 4-stage drag torque characteristic curve is illustrated to show the dominant factors of drag torque at different stages.
TOPICS: Torque, Drag (Fluid dynamics), Plates (structures), Vibration, Lubricants, Flow (Dynamics), Friction, Rotation, Shear (Mechanics), Clearances (Engineering)
Achhaibar Singh
J. Fluids Eng   doi: 10.1115/1.4037058
Mathematical relations are obtained for velocities and pressure distribution for a fluid entering the peripheral clearance of a pair of rotating concentric disks that converges and discharges through an opening at the center. Both, the flows in the gap of corotating disks and in the gap of contrarotating disks can be predicted using the present analytical solutions. The prediction of instability of radial velocity for corotating disks at speed ratio of unity is very important for practical applications. Radial velocity profile is similar to a parabolic profile exactly at speed ratio of unity. The profile drastically changes with the small difference of ±1% in the disks rotation. The radial convection was observed in tangential velocity at a low radius. Centrifugal force caused by disk rotation highly influences the flow resulting in backflow on the disks. The pressure consists of friction losses and convective inertia. Therefore, the pressure decrease is high for increased speed ratio, throughflow Reynolds number and rotational Reynolds number. The pressure decrease for the flow between contrarotating disks is lesser than that for the flow between corotating disks due to decreased viscous losses in the tangential direction. This study provides valuable guidance to the design of devices where disks are rotated independently by highlighting the instabilities in the radial velocity at speed ratio of unity.
TOPICS: Inertia (Mechanics), Pressure, Rotation, Flow (Dynamics), Friction, Fluids, Centrifugal force, Reynolds number, Clearances (Engineering), Convection, Design, Disks, Rotating Disks, Inflow
Rajesh Ranjan and Roddam Narasimha
J. Fluids Eng   doi: 10.1115/1.4037059
The phenomenon of relaminarization is observed in many flow situations, including that of an initially turbulent boundary layer (TBL) subjected to strong favourable pressure gradients (FPG). As several experiments on relaminarizing flows have indicated, TBLs subjected to high pressure gradients do not follow the universal log-law, and (for this and other reasons) the prediction of boundary layer parameters using RANS-type models has not been successful. However, a quasi-laminar theory (QLT; proposed in 1973), based on a two-layer model to explain the later stages of relaminarization, showed good agreement with the experimental data available at that time. These data were mostly at relatively low Re, and hence left the precise role of viscosity undefined. QLT, therefore, could not be assessed at high Re. Recent experiments, however, have provided more comprehensive data and extended the Reynolds number range to nearly 5 x 10 ^3 in momentum thickness. These data provide a basis for a reassessment of QLT, which is revisited here with an improved predictive code. It is demonstrated that even for these high-Re flows subjected to high acceleration, QLT provides good agreement with experimental results, and therefore has the potential to supplement RANS simulations in high FPG regions.
TOPICS: Momentum, Flow (Dynamics), Viscosity, Reynolds number, Simulation, High pressure (Physics), Boundary layers, Engineering simulation, Boundary layer turbulence, Pressure gradient, Reynolds-averaged Navier–Stokes equations
Eissa M. Al-Safran, Ahmad Aql and Tan Nguyen
J. Fluids Eng   doi: 10.1115/1.4037057
A progressing cavity pump (PCP) is a positive displacement pump with an eccentric screw movement, which is used as an artificial lift method in oil wells. Downhole PCP systems provide an efficient lifting method for heavy oil wells producing under cold production, with or without sand. Newer PCP designs are also being used to produce wells operating under thermal recovery. The objective of this study was to develop a set of theoretical operational, fluid property, and pump geometry dimensionless groups that govern fluid flow behavior in a PCP. A further objective was to correlate these dimensionless groups to develop a simple model to predict flow rate (or pressure drop) along a PCP. Four PCP dimensionless groups, namely Euler number, inverse Reynolds number, Specific Capacity number, and Knudsen number were derived from continuity, Navier-Stokes equations, and appropriate boundary conditions. For simplification, the Specific Capacity and Knudsen dimensionless groups were combined in a new dimensionless group named the PCP number. Using the developed dimensionless groups, non-linear regression modeling was carried out using large PCP experimental database to develop dimensionless empirical models of both single- and two-phase flow in a PCP. The developed single-phase model was validated against an independent single-phase experimental database. The validation study results show that the developed model is capable of predicting pressure drop across a PCP for different pump speeds with 85% accuracy.
TOPICS: Fluid dynamics, Pumps, Cavities, Databases, Pressure drop, Oil wells, Vacuum pumps, Geometry, Two-phase flow, Boundary-value problems, Flow (Dynamics), Fluids, Sands, Wells, Screws, Reynolds number, Knudsen number, Navier-Stokes equations, Modeling
S M Aravind Kumar and Ethirajan Rathakrishnan
J. Fluids Eng   doi: 10.1115/1.4036823
Nozzle aspect ratio effect on the mixing of Mach 2 elliptic free jet, issuing from the convergent-divergent elliptic nozzles of aspect ratio 2, 3 and 4, in the presence of adverse and marginally favorable pressure gradients at the nozzle exit has been studied experimentally. The results show that AR4 jet enjoys better mixing than AR2 and AR3 jets at all nozzle pressure ratios. The AR2 and AR3 jets displayed axis switching where as there is no axis switching for AR4 jet. The shadowgraph shows that the waves in AR4 jet are weaker than those in AR2 and AR3 jets.
TOPICS: Nozzles, Jets, Pressure gradient, Pressure, Waves
M . C. Keerthi, Abhijit Kushari and Valliammai Somasundaram
J. Fluids Eng   doi: 10.1115/1.4036827
The intakes of modern aircraft are subjected to ever-increasing demands in their performance. To avoid a penalty in engine performance, the flow through the intake needs to be controlled using various methods of flow control. In the present study, a serpentine intake is studied experimentally and its performance compared with and without boundary layer suction. The performance parameters used are the non-dimensional total pressure loss coefficient and standard total pressure distortion descriptors. The effect is observed on the stream-wise surface pressure distributions and inferences are made regarding the separation location and extent. The Suction has been applied at three different locations, spanning different number of ports along each location, comprising of ten unique configurations. The mass flow rate of suction employed ranges from 1.1 to 6.7 % of the mass flow rate through the intake. The effect is seen on the exit total pressure recovery as well as the circumferential and radial distortion parameters. This is examined in the context of the location of the suction ports and amount of suction mass flow, by the deviation in surface pressure distributions, as well as the separation characteristics from the baseline case. The results show that applying suction far upstream of the separation point together with a modest amount of suction downstream results in the best performance.
TOPICS: Suction, Flow control, Pressure, Flow (Dynamics), Separation (Technology), Gates (Closures), Boundary layers, Aircraft, Engines
Seyed Sobhan Aleyasin, Mark F. Tachie and Mikhail Koupriyanov
J. Fluids Eng   doi: 10.1115/1.4036824
An experimental study was conducted to investigate the effect of nozzle geometries on the statistical properties of free orifice jets at low and moderate Reynolds numbers. The studied cross_sections were round, square and ellipses with aspect ratios of 2 and 3. For each jet, detailed velocity measurements were made using a particle image velocimetry system at Reynolds numbers of 2500 and 17000. The results showed that at both Reynolds numbers the elliptic jets had relatively higher velocity decay and jet spreading; however, the nozzle geometry effects were more pronounced at Re = 17000 than at Re = 2500. Analysis of the swirling strength revealed that the rotational motions induced by vortices within the minor planes of the elliptic jets were stronger than observed in the major planes, square and round jets which were consistent with the relatively higher spreading observed in the minor planes. It was observed that the streamwise locations of the switchover points were independent of Reynolds number but are a strong function of aspect ratio. Based on the present results and those documented in the literature, a linear correlation was proposed for the location of axis-switching in orifice jets. Due to the axis-switching phenomena, a sign change was observed in the distribution of the Reynolds shear stress in the major planes of the elliptic jets. This results in the existence of regions with negative eddy viscosity in the near field regions, an observation that has an important implication for the predictive capabilities of standard eddy viscosity models.
TOPICS: Reynolds number, Jets, Nozzles, Eddies (Fluid dynamics), Viscosity, Rotation, Particulate matter, Vortices, Geometry, Swirling flow, Velocity measurement, Shear stress
Hao Tian and James D. Van de Ven
J. Fluids Eng   doi: 10.1115/1.4036711
The bulk modulus of hydraulic fluid is dependent on the quantity of entrained gas in the fluid. In this paper, an effective fluid bulk modulus model that captures dynamic gas absorption during pressure transients is derived from the overall mass transfer theory. Optical measurement of a micro gas bubble volume is used to determine the interfacial mass transport. Compared to traditional models, the proposed model is able to capture the 10% gap in the pressure profile between the first and second cycles, when simulating multiple compression cycles of an oil sample with 0.65% entrained gas by volume at 8 MPa.
TOPICS: Compressibility, Fluids, Absorption, Modeling, Cycles, Bulk modulus, Pressure, Compression, Transients (Dynamics), Bubbles, Optical measurement, Mass transfer
Yi Ma, Huashuai Luo, Tao Gao and Zhihong Zhang
J. Fluids Eng   doi: 10.1115/1.4036715
In petroleum industry, the stability of multiphase pumping is highly disturbed by the gas presence with high content and variable working conditions. This paper is focused on studying the whole working cycle of the novel three-cylinder double-acting reciprocating multiphase pump. Based on the theoretical analysis, the method of computational fluid dynamics is adopted to simulate the oil-gas flow in reciprocating multiphase pump. The numerical methodology, involving multiphase model, dynamic grid technique and user defined functions, is used to deal with in the calculation. The transient flow characteristics in pump cavity are obtained, and the flow ripples of reciprocating multiphase pump are analyzed. Furthermore, the effects of different operating parameters, such as suction and discharge pressures, inlet gas volume fraction on the capacity and stability of pump are studied. The results could help to develop and optimize the high-efficiency multiphase pump system.
TOPICS: Pumps, Cylinders, Unsteady flow, Stability, Flow (Dynamics), Suction, Computational fluid dynamics, Petroleum industry, Theoretical analysis, Cavities, Cycles
Adam Ritcey, Joesph R. McDermid and Samir Ziada
J. Fluids Eng   doi: 10.1115/1.4036717
The maximum skin friction and flow field is experimentally measured on a planar impinging gas jet using oil film interferometry (OFI) and particle image velocimetry (PIV), respectively. A jet nozzle width of W = 15 mm, impingement ratios H=W = 4;6;8; 10, and a range of jet Reynolds numbers Rejet = 11000- 40000 is tested to provide a parametric map of the maximum skin friction. The maximum skin friction predictions of Phares et al. [1] for plane jets agree within 5 % of the current OFI results for H=W = 6, but deviates upwards of 28 % for other impingement ratios. The maximum skin friction is found to be less sensitive to changes in the impingement ratio when the jet standoff distance is roughly within the potential core length of the jet. PIV measurements show turbulence transition locations moving towards the nozzle exit with increasing Reynolds number, saturation in the downstream evolution of the maximum axial turbulence intensity before reaching a maximum peak upon impingement, followed by sudden damping at the plate surface. As the flow is redirected, there is an orthogonal redistribution of the fluctuating velocity components, and local peaks in both the axial and transverse turbulence intensity distributions at the plate locations of the maximum skin friction.
TOPICS: Flow (Dynamics), Skin friction (Fluid dynamics), Turbulence, Reynolds number, Nozzles, Jets, Damping, Interferometry, Particulate matter
Johan Pretorius, Gazi I. Mahmood and Josua P. Meyer
J. Fluids Eng   doi: 10.1115/1.4036671
Standard pin-fins in the heat transfer channels are shaped to reduce the pressure penalty and increase the thermal performance. The paper presents experimental results of the wall-static pressure distributions in an array of modified cylindrical short pin-fins in a channel. Standard cylindrical pin-fins with a smooth surface and a similar array configuration are also evaluated as a baseline for comparisons. The pin-fins with a height to diameter ratio of 1.28 are arranged in a staggered array consisting of 13 rows in a rectangular channel of aspect ratio 1:7.8. The cylindrical pins are modified by the machined slots at the tips. The slots in the pins are aligned in the streamwise direction. The static pressure distributions are measured on the endwall between the pin-rows and on the pin surface. The Reynolds number based on the channel hydraulic diameter ranges from 10,000 to 50,000. The slots in the pins reduce the friction factor and wall-static pressure drop between the pin-rows by up to 50%. The objectives of the investigation are to reduce the pressure penalty in the cylindrical pin-fin channel to provide increased thermal performance.
TOPICS: Pressure, Pins (Engineering), Fins, Pressure drop, Friction, Heat transfer, Reynolds number

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