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Ashok K. Singhal

Bio: Ashok K. Singhal is an academic researcher. The author has contributed to research in topics: Computational fluid dynamics & Cavitation. The author has an hindex of 3, co-authored 3 publications receiving 1268 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors present the full cavitation model, which accounts for all the first-order effects of cavitation and is called as the full-cavitation model and the phase change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics.
Abstract: Cavitating flows entail phase change and hence very large and steep density variations in the low pressure regions. These are also very sensitive to: (a) the formation and transport of vapor bubbles, (b) the turbulent fluctuations of pressure and velocity, and (c) the magnitude of noncondensible gases, which are dissolved or ingested in the operating liquid. The presented cavitation model accounts for all these first-order effects, and thus is named as the full cavitation model. The phase-change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics. These rates depend upon local flow conditions (pressure, velocities, turbulence) as well as fluid properties (saturation pressure, densities, and surface tension). The rate expressions employ two empirical constants, which have been calibrated with experimental data covering a very wide range of flow conditions, and do not require adjustments for different problems. The model has been implemented in an advanced, commercial, general-purpose CFD code, CFD-ACE+

1,329 citations

Journal ArticleDOI
TL;DR: In this article, a full cavitation model was developed for performance prediction of engineering equipment under cavitating flow conditions, and the model was incorporated into an advanced finite-volume, pressure-based, commercial CFD code (CFD - ACE +) that uses unstructured/hybrid grids to integrate the N-S equations.
Abstract: A new "full cavitation model" has been recently developed for performance predictions of engineering equipment under cavitating flow conditions. A vapor transport equation is used for the vapor phase and it is coupled with the turbulent N-S equations. The reduced Rayleigh-Plesset equations are used to account for bubble formation and to derive the time-mean phase-change rates utilizing the local pressures and characteristic velocities. Effects of turbulent fluctuations and noncondensable gases are also included to make the model complete. The model has been incorporated into an advanced finite-volume, pressure-based, commercial CFD code (CFD - ACE +) that uses unstructured/hybrid grids to integrate the N-S equations. Full model details are being published separately. Presented here are simulations of cavitating flows in three types of machines: water jet propulsion axial pump, a centrifugal water pump, and an inducer from a LOX turbo pump. The results show cavitation zones on the leading edgesuction side of each of the machines as expected. Simulations at different suction specific speeds were performed for the waterjet pump and the inducer and showed the proper trends of changes in cavity strength and sizes. All the test cases with cavitation show plausible results (no negative pressures, and good convergence characteristics). Computations on the waterjet pump for different noncondensible gas concentrations showed sizeable changes in the pump head developed.

70 citations

Journal ArticleDOI
TL;DR: Main strengths and shortcomings of present thermal hydraulic analysis methodology are summarized, areas for further research and development are suggested, and topics reviewed include geometry representation of U-tube and once-through steam generators for three-dimensional analysis.

17 citations

Proceedings ArticleDOI
10 Mar 2023
TL;DR: The Toe-To-Heel Air Injection (THAI) process as mentioned in this paper is a novel in-situ combustion (ISC) process, which uses vertical air injectors and horizontal producers.
Abstract: The paper describes the first field piloting of the Toe-To-Heel Air Injection (THAI) process - a novel in-situ combustion (ISC) process, which uses vertical air injectors and horizontal producers. The pilot (located in the Athabasca region of Canada) consisted of three adjacent pairs of vertical-horizontal well arranged in a direct line drive configuration, with a lateral spacing of 100m. An in-depth analysis was performed for the determination of the ignition delay during initiation of the ISC via enhanced spontaneous ignition using a steam slug injection. Numerous bottomhole temperatures (BHT) recordings from 11 observation wells allowed to establish the loss of air in an upper formation and the lateral development of the burned zone. Using many thermocouples located along the horizontal section of producers, the determination of the ISC front advancement along the horizontal drains was possible. Based on this, a rough estimate of the volumetric sweep was made. Due to sand influx and other factors, all horizontal producers were replaced; the period of air injection stoppage - during the drilling of replacement producers – caused a substantial modification of the process. Initiation of ISC process by spontaneous ignition occurred within 1-2 months. A robust ISC was generated and sustained during the five-year piloting. Oxygen utilization was almost 100%, indicating a remarkable stability of the process. The lateral development of the burned zone was limited, within 20 m laterally off the horizontal producer trajectory. The ISC front advanced approximately half of the distance toe-heel, along the horizontal section. Loss of air vertically, led to the formation of a secondary ISC front in an upper formation with no production outlets (production wells). This loss of air and the presence of a thin bottom water zone (from which a significant amount of water was produced) decreased the efficiency of the process. During the air injection interruption (3-4 months), a pronounced pressure decline in the burnt-out zone caused its oil re-saturation leading to coke deposition and blockage; subsequent ISC front propagation along the replacement wells was not satisfactory and these wells did not improve the performance. The pilot confirmed the laboratory findings regarding the production of in-situ upgraded oil and, revealed that THAI generates significant amounts of hydrogen as part of the produced gases. Upgrading of the produced oil was in the range of 2° to 8° API., while the oil viscosity decreased 220 times, from 550,000cp to 2500cP The oil recovery from the pilot was estimated at 7%. In its stabilized phase, the effective oil rate per well was 10-20 m3/day, as compared with 3-4 m3/day in all previous old ISC trials in Athabasca. The air-oil ratio was in the range of 5,000 to 6,000 sm3/m3. It is the first time that day-by-day in-situ upgrading is fully validated in the oil field. Therefore, THAI is the first EOR process fully proven for producing underground upgraded oil without using any additional exterior heat sources.

Cited by
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Journal ArticleDOI
TL;DR: In this paper, the authors present the full cavitation model, which accounts for all the first-order effects of cavitation and is called as the full-cavitation model and the phase change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics.
Abstract: Cavitating flows entail phase change and hence very large and steep density variations in the low pressure regions. These are also very sensitive to: (a) the formation and transport of vapor bubbles, (b) the turbulent fluctuations of pressure and velocity, and (c) the magnitude of noncondensible gases, which are dissolved or ingested in the operating liquid. The presented cavitation model accounts for all these first-order effects, and thus is named as the full cavitation model. The phase-change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics. These rates depend upon local flow conditions (pressure, velocities, turbulence) as well as fluid properties (saturation pressure, densities, and surface tension). The rate expressions employ two empirical constants, which have been calibrated with experimental data covering a very wide range of flow conditions, and do not require adjustments for different problems. The model has been implemented in an advanced, commercial, general-purpose CFD code, CFD-ACE+

1,329 citations

Journal ArticleDOI
TL;DR: In this paper, the cavitating flow around a NACA66 hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics, including the cavity growth, break-off and collapse downstream.

335 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarized the recent progress for the cavitation study in the hydraulic machinery including turbo-pumps, hydro turbines, etc., and identified the 1-D analysis method, which is identified to be very useful for engineering applications regarding the cavitating flows in inducers, turbine draft tubes, etc.
Abstract: This paper mainly summarizes the recent progresses for the cavitation study in the hydraulic machinery including turbo-pumps, hydro turbines, etc.. Especially, the newly developed numerical methods for simulating cavitating turbulent flows and the achievements with regard to the complicated flow features revealed by using advanced optical techniques as well as cavitation simulation are introduced so as to make a better understanding of the cavitating flow mechanism for hydraulic machinery. Since cavitation instabilities are also vital issue and rather harmful for the operation safety of hydro machines, we present the 1-D analysis method, which is identified to be very useful for engineering applications regarding the cavitating flows in inducers, turbine draft tubes, etc. Though both cavitation and hydraulic machinery are extensively discussed in literatures, one should be aware that a few problems still remains and are open for solution, such as the comprehensive understanding of cavitating turbulent flows especially inside hydro turbines, the unneglectable discrepancies between the numerical and experimental data, etc.. To further promote the study of cavitation in hydraulic machinery, some advanced topics such as a Density-Based solver suitable for highly compressible cavitating turbulent flows, a virtual cavitation tunnel, etc. are addressed for the future works.

296 citations

Journal ArticleDOI
TL;DR: In this article, the structure of the cavitating flow around a twisted hydrofoil was investigated numerically using the mass transfer cavitation model and the modified RNG k-e model with a local density correction for turbulent eddy viscosity.

277 citations

Journal ArticleDOI
Bin Ji1, Xianwu Luo1, Yulin Wu1, Xiaoxing Peng, Yunling Duan1 
TL;DR: In this paper, the Partially-Averaged Navier-Stokes (PANS) method and a mass transfer cavitation model with the maximum density ratio ( ρ l / ρ v,clip ) effect between the liquid and the vapor were used to simulate cavitating turbulent flow around hydrofoils.

249 citations