Drop In Head Research Articles

Geothermal Potential of Pumping–Injecting Doublet Wells

A characteristic of the Pannonian Basin is its strong geothermal flow. Geothermal water is present in aquifers in the Miocene and Pliocene sediments of the Lendava, Murska Sobota, and Mura formations, as well as in pre-Neogene sedimentary rocks, at a depth of several 1000 s to several 100 s of meters. The water from the deep Miocene and Pliocene aquifers is mainly pumped for use in the spas of the region, which is separated by national borders. Pumping water from the aquifers lowers the hydraulic head of the water in the aquifers. The consequence of the drop in hydraulic head is a reduction in the yield of the aquifers, which has a negative impact on the neighboring wells. In order to prevent the effects of this influence—especially in the case of transboundary influences, as in our case—the construction of an additional well was proposed, through which the cooled water would be pumped back into the deep aquifer. For the specific case of the Terme Korovci project, which is located directly on the national border, a 3D structural model of the aquifer was created. The hydrogeological and thermal properties of the aquifer were determined on the basis of the lithological profile of the wells in the region, along with well logs and pumping tests. As detailed data on the thicknesses of the layers have not been available until now, we have envisaged several scenarios for different layer thicknesses. As will be evident from our data, in the case of a 10 m-thick layer, the temperature falls to below 70 °C in fewer than 6000 days, and this period extends with increasing thickness such that with a 200 m-thick layer, the period extends to well over 100,000 days. The findings are important because the potential investor requires at least 20 years of operation of the pumping–reinjection pair of wells.

Flexible structures enhance fluid mixing in a channel flow

Early fluid mixing in channel flows without incurring much drop in the pressure head is desired in industrial applications. This study explores wall-mounted flexible plates as obstacles to enhance mixing in channel flows. Using fluid–structure-scalar interaction simulations, we investigate the oscillations of the flexible plates under the flow, which serve as a vortex generator and help increase the mixing. The channel flow involves a scalar field with distinct concentrations initially separated across the channel, gradually intermixing due to vortical structures of varying scales. We have used the “mixing index” and “head loss” metrics along the channel length to assess the mixing quality when plates with different flexibility (characterized by the Cauchy number, Ca) are used. This study introduces a comprehensive criterion, the “coefficient of performance,” derived by comparing mixing and head loss in the presence and absence of obstacles. Aggregating results across various Ca values reveal that flexible plates substantially improve fluid mixing compared to rigid plates. We have also investigated the effect of the pulsatile fluid inlet (quantified by Strouhal number, Stf) and found that lower inlet flow pulsation (Stf<32) adversely impacts mixing performance, recommending a steady inlet flow. However, at high Stf, specifically in the configuration with Ca = 0.06 and Stf = 32, the best mixing performance is achieved in the channel, which marginally outperforms the steady inlet case. The conclusive takeaways from this study are that the plates with increased flexibility result in better mixing, and high inlet pulsation can be employed to fine-tune the mixing performance for further enhancement.

Modeling of seawater intrusion into Salalah coastal plain aquifer, sultanate of Oman

Excessive groundwater pumping has become a concern in Salalah coastal aquifer in Oman causing seawater intrusion at different farms and abstraction wells near the shoreline. MODFLOW and MT3DMS were calibrated and validated for Salalah coastal aquifer to assess aquifer behavior and seawater intrusion pattern with new input data and fine grid spacing to improve the accuracy of predictions as compared to the previous modeling studies in this region. The study was conducted over an area of 640 km2 of Salalah Plain representing around 83% of its total area. Injection of tertiary treated wastewater, rainfall and dams were considered as sources of aquifer recharge while groundwater abstraction occurred for agricultural, domestic, and commercial uses. The calibration and validation of the models were done in steady and transient states using observed groundwater levels from year 2000–2019. The aquifer properties such as hydraulic conductivity, specific yield, and vertical anisotropy were calibrated. MODFLOW results were utilized by MT3DMS to simulate solute transport at transient state. The longitudinal dispersivity and porosity of the aquifer were obtained by calibration and validation of the model. Over the three aquifer layers, the hydraulic conductivity ranges from 10 m/day to 100 m/day, vertical anisotropy is 4 and the specific yield ranges from 0.01 to 0.1. The calibrated values of the longitudinal dispersivity and porosity range from 500 m to 50000 m, and 0.4, respectively. The study indicated a clear impact of seawater intrusion at coastal side of the Salalah plain. The predictive modeling indicated an average of 1.5 m drop in hydraulic head across the whole study area by 2040, while seawater intrusion effect was expected to increase near the coast with potential extension to the central area of the Salalah plain. The validated model can be used as a prediction tool by the decision makers to manage the aquifer considering different scenarios, for integrated water resources management in Salalah city.

Seepage Quantity Analysis Beneath Concrete Dams with Various Sheet Piles using Different Numerical Models

Seepage is a dangerous phenomenon under hydraulic structures and the main cause of failure and damage to dams when neglected and not processed. This study evaluates the numerical effects of the sheet piles' quantity, depth, and spacing beneath a concrete dam with isotropic and homogenous foundations on the seepage rate, pressure head, and exit gradient. The solutions were obtained using SEEP/W code in GeoStudio software 2018 for three configurations using single, double, and triple sheet piles. In addition, SLIDE software 6.02 was examined using single and double sheet piles. Dimensional analysis was applied to draw the dimensionless variables that affect the seepage rate and exit gradient, and all tests were repeated for three different sheet pile depths and distances from the heel of the dam. The findings showed that the seepage rate in all studied configurations reduced when sheet pile depth increased. The position of the sheet pile from the dam's toe significantly decreased the seepage rate in cases using single and double sheet piles, while in cases using three-sheet piles, the position of the middle sheet pile insignificant decreased seepage. It was recognized that when using a single sheet pile, the drop in pressure head increased with depths when the sheet pile was located at the heel and middle of the dam. In addition, in the case of a single sheet pile at the toe or using two and three-sheet piles, the pressure drop decreased as the depths increased. Also, the results showed that the middle sheet pile location in the case of three sheet piles slightly affected pressure reduction. Furthermore, the results showed that using two and three-sheet piles was more effective than using a single one in reducing the exit gradient, while the position of the middle one in the case of using three-sheet piles was insignificant. A nonlinear empirical equation was developed using SPSS 22 program, and the comparison of the seepage rate measured by SEEP/W and SLIDE software versus its quantity calculated from empirical equations showed a good agreement as the determinations (R2) coefficients were equal to 0.9779 and 0.9928, respectively.

Multi-objective optimization of a two-stage liquefied natural gas cryogenic submerged pump-turbine in pump mode to reduce flow loss and cavitation

To simultaneously minimize the energy loss and optimize the suction performance in a two-stage LNG (liquefied natural gas) cryogenic submerged pump-turbine in pump mode (PTP), a multi-objective optimization work containing numerical models of cryogenic cavitation flow, novel suction performance prediction, entropy production diagnosis and multi-criteria decision-making method is conducted to obtain the optimal geometric variables, as well as the corresponding performances under 0.7 Q0 with typical growth trend in energy loss after cavitation. Results show that the inlet angle β1 at the shroud and the arc section radius of the shroud r1 of the first-stage impeller and the wrap angle Φ at the shroud of the second-stage impeller are the significant parameters affecting the energy loss and suction performance of the PTP. Then, the ideal compromise solution, β1 = 14.34°， r1 = 26.28 mm and Φ = 127.44°, is obtained by multi-objective optimization and decision-making. The active suppression of the impinging flow, flow separation and rotating stall in the two-stage impellers after optimization yields a 6.18 % drop in the total entropy production rate with sacrificing a 1.25 % drop in pump head. In addition, the PTP is more likely to maintain a better suction performance for the optimal design over a wide range of flow rates. This research contributes to the search for the tradeoff between the conflicting hydraulic performance of the multistage pump-fed unit.

Effect of Bionic Nonsmooth Surface Vane on the Antiwear Characteristics of Double-Vane Pump.

In order to improve the antiwear characteristics of the double-vane self-priming pump, the surface structure of the Scapharca subcrenata was extracted and reconstructed according to bionic principles. Three types of nonsmooth surface models were established at the outlet end of the suction surface of the vanes, which is the most severely worn in the double-vane pump. The external characteristics, pressure field distribution, wear area distribution, and wear degree of the volute and vanes at different concentrations of nonsmooth vane structure were investigated by numerical simulation to reveal the mechanism of the nonsmooth surface structure of the wear characteristics of the vanes. The results show that the head and efficiency of pumps with four different vanes decrease and the average wear rate increases as the particle concentration increases. The different vane structures have a very small effect on the wear resistance of the volute, but a larger effect on vane wear. The circular nonsmooth surface structure, which reduces the low pressure area of the inlet section of the impeller while ensuring a smaller drop in head and efficiency, produces the best antiwear effect and improves the antiwear performance of the double-vane pump.

The external characteristics and inner flow research of rim-driven thruster

In order to have a more comprehensive grasp of the performance of the rim-driven thruster, the external characteristics are studied by experiment and carry out numerical simulation to study inner flow characteristics. The test results for the rim-driven thruster find that the head curve had a hump shape. The head is the largest while the flow rate Q = 600 m3/h. The numerical simulation is carried out to reveal the cause of the hump of head. The results show that large-scale backflows gradually appear near the wall in front of the impeller inlet, the central area of the impeller outlet, and the two sides of the central low-pressure zone with the reducing of the flow rate, which can cause a large flow loss and result in a drop in head. The discrepancy between the pressure surface and the suction surface of blade decreases rapidly in the range of r/ R = 0.2–0.5, which is another major factor leading to the drop in head under small-flow conditions. Structurally, there is no blade in the impeller center and there are the large backflows in the middle of impeller, which causes much volume loss and is a main cause of the decreasing of head under small flow rate.

Internal Flow and Hydraulic Loss of Centrifugal Pumps with Radial and Annular Flow Channel Impeller

To provide stable operation over a wide flow range, centrifugal pumps should have high pump efficiency at a low flow rates and high total head. A new impeller with radial and annular flow channels that has higher pumping performance than conventional design impellers with the same specific speed and flow rate at a low specific speed was proposed. however, a high unsteady flow was observed inside the pump. In this study, to predict performance, unsteady CFD was used to investigate pump performance, including different hydraulic losses. The results show that pump performance can be estimated more accurately using unsteady CFD than using steady CFD. The constant drop in total head with flow rate is owing to the hydraulic losses in the impeller, which exclude friction, growing in proportion to flow rate.

Study of the field hydraulic conductivity of thin open-graded friction courses

Permeability of asphalt pavements is a property of interest due to its impact on durability and, potentially, safety. In the case of open-graded friction courses (OGFC), the focus with permeability is on the improved drainage capacity that reduces splash and spray, and hydroplaning potential. Multiple research efforts have developed permeameters to evaluate field permeability. However, most of these efforts consider unidirectional linear Darcy flow, which is not sufficient to describe flow through OGFC layers during testing conditions. The objective of this investigation was to examine the use of an approximate analytical solution based on 2D flow proposed by researchers at UT-Austin to study the field permeability of thin OGFC layers. Additional values for a shape factor were proposed to test relatively large areas of thin OGFC layers. Furthermore, it was found that the use of vacuum grease to prevent water flow between the base of the permeameter and the pavement surface clogged the OGFC surface voids, which notably reduced hydraulic conductivity. To overcome this issue, this study evaluated the use of a closed-cell high-density foam pad as a sealant method. Lastly, the study showed the need for a minimum volume of water to provide a smooth drop in water head during testing. This is necessary to allow for accurate measurement of the three time readings required to describe the nonlinear relationship between elevation head and flow rate during a falling-head permeability test. The lessons learned from this study were summarized in a set of guidelines for the successful development of a new permeameter. These guidelines can be used by other highway agencies interested in evaluating the field hydraulic conductivity of thin OGFC layers.

Relationship between Visual Cavitation Inception and 3% Drop in Head in Centrifugal Pumps (Dept.M)

Pumps were designed and manufactured to operate far from the cavitation condition. Pump designer has defined the cavitation inception point as the point where the head drops by 3 %. This definition is incorrect, because the first appearance of vapour bubbles was observed earlier than 3% drop in the head. Therefore using 3 % drop in head, as indication parameter for cavitation inception has always resulted in damage in pumps during operation. This paper describes visual studies conducted to determine the variation of net positive suction head with flow rate, rotational speed and water temperature. A special correlation between the visual net p ositive suction head and net positive suction head corresponding to 3 % drop in head was predicted at various operating conditions.

Experimental Investigation of the Effect of Air Injection on Performance and Detection of Cavitation in the Centrifugal Pump Based on Vibration Technique

Cavitation is a problem that occurs in any pump and contributes highly towards the deterioration in the performance of the pump. In industrial applications, it is vital to detect and minimize the effect of cavitation in pumps. The use of various techniques, such as vibration analyses, can provide a more robust detection of cavitation in the pump. In this work, the effect of air injection at the inlet of the pump on its performance has been focused by detecting and diagnosing the cavitation using vibration technique. The results obtained for vibration signal in time and frequency domains were analysed in order to achieve a better understanding regarding detection of cavitation. The effects of different operating conditions related to the cavitation were investigated in this work using different statistical features in time domain. Moreover, fast Fourier transform technique for frequency domain was also applied. The results showed that there is no significant change between both cases (with and without air injection) when the pump works under low flow operating conditions. However, there is a slight difference between both cases after 300(l/min) and drop in the pump head for air injection was noticed as compared to without air injection condition. Moreover, the development of cavitation starts at higher design flow and it will increase when flow rate is increased more than 350(l/min). The trend of vibration signal amplitude was more random with high peaks when compared with normal operating conditions (without cavitation).

Unsteady flow characteristics and cavitation prediction in the double-suction centrifugal pump using a novel approach

The recent advances in centrifugal pump design do not only require a better suction performance but also there have been attempts to reduce design time at a lower cost. The traditional trial-and-error optimization design method, however, depends on the designer's experience, which requires longer cycles. This is because the computational process of calculating the net positive suction head required (NPSHr) involves several calculation steps and this consumes a lot of computational time. An investigation was therefore carried out to test a novel NPSHr prediction method in a double-suction centrifugal pump using unsteady numerical simulations. In the new approach, a new boundary pair was introduced and an algorithm was used to estimate a good value for a static pressure value that correlates to a 3% drop in pump head to determine the critical cavitation point. Experiments were conducted to validate the hydraulic performance and the cavitation model. The NPSHr and the characteristic “sudden” head-drop were very well predicted by the novel approach in only three simulation steps. The internal flow analysis showed that for 0.6 Q d, the flow around the volute tongue was uneven at NPSH = 10.06 m, inducing flow separation and recirculation at the tongue region. Attached cavities were also observed around the suction ring in the spiral suction domain. The pressure fluctuations were analyzed also and the dominant frequency at the pump outlet and tongue region was the blade passing frequency. Consequently, the novel approach proved very robust and efficient in NPSHr prediction and would be a good alternative to shorten simulation time during cavitation optimization design process in centrifugal pumps.

Detection of Cavitation through Acoustic Generation in Centrifugal Pump Impeller

The most common device which transport fluid in industries, agriculture as well as domestic water supply is the centrifugal pump. Based on fluid transfer conditions, several let-downs are occur in the centrifugal pump, cavitation is one among them. The flow pattern at the eye of impeller deviates from the ideal case with the occurrence of cavitation. Due to cavitation, vibration occurs on blades that generates noise in pump. In this study, the acoustics generated in centrifugal pump impeller due to cavitation is detected with the sound pressure by using 3-Dimensional, steady and unsteady state computational fluid dynamics (CFD) analysis of an industrial centrifugal pump impeller. Harmonic force analysis with blade row model helps in finding the sound pressure. The acoustics generated with unsteady-state is compared with cavitation at steady-state CFD analysis. The Reynolds averaged Navier-Stokes equations model as well as Shear Stress Transport (SST) turbulence model are used for the CFD simulation. The results show that the sound pressure calculated increases with the increase in cavitation (i.e. formation of vapour bubbles and sudden drop in head) which shows that high noises are generated by centrifugal pump impeller at lower net positive suction head (NPSH) at a particular discharge.

Monitoring and Water Table Control For Plantation on Peatland in Indonesia

Drainage construction for plantations development on peatlands often caused controversy. Dranage construction will be followed by subsidence of peatland . To be able to extend the chance to get profit in the plantation business subsidence prevention efforts are needed. Setting water level and the prevention of excessive drainage is one of the efforts to reduce the rate of subsidence of the peat.This study is based on literature review by collecting information from various sources and then comparing and analyzing it so that information is obtained on a comprehensive subject matter. Literature review include: monitoring parameters, types of equipment for monitoring, pattern placement monitoring equipment, the range and the frequency of monitoring. From the study concluded that the water level necessary to measure on land and channels using dipwell and staff gauges. Observations were made with a combination of automated recording device and manual recording. Both are quite accurate, but the use of automatic registers in remote locations saves time, and if an automatic device is installed in an area that has the potential to have large water level fluctuations and runs quickly, it will provide more accurate data. Observations on dams for water level control are installed at every 20 cm drop in hidraulic head.

Numerical and experimental investigation of cavitation flows in a multistage centrifugal pump

Cavitation behavior is very important in pumps for long time operation. However, there is difficulty in predicting the cavitation phenomena of pumps by Computational fluid dynamics (CFD). In order to accurately ascertain cavitation behavior, a comparison between CFD and experimental data is a significant and essential process. The purpose of this study is to analyze cavitating behavior in multistage centrifugal pumps numerically and experimentally. For this investigation an experimental set up was used to obtain cavitation performance results. The CFD method was used to investigate the multistage centrifugal pump performance under developed cavitating conditions. The Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was adopted to account for turbulent flows. Numerical data were validated with experimental data and a good comparison of results was achieved. Numerically, cavitation performances were obtained for different pump stages and the effects on cavitation were described according to different NPSH (Net positive suction head). The occurrence of cavitation was also described according to NPSH3% in the head drop lines and water vapor volume fraction on the impeller blade. The rapid drop in head at low NPSH was captured for different flow conditions. It was found that for stage to stage performance, the head drop changes could be related to losses inside the pump. It was also shown that the simulation results can truly represent the development of the attached sheet cavitation in the impeller.

Nonlinear consolidation in randomly heterogeneous highly compressible aquitards

Severe land subsidence due to groundwater extraction may occur in multiaquifer systems where highly compressible aquitards are present. The highly compressible nature of the aquitards leads to nonlinear consolidation where the groundwater flow parameters are stress-dependent. The case is further complicated by the heterogeneity of the hydrogeologic and geotechnical properties of the aquitards. The effect of realistic vertical heterogeneity of hydrogeologic and geotechnical parameters on the consolidation of highly compressible aquitards is investigated by means of one-dimensional Monte Carlo numerical simulations where the lower boundary represents the effect of an instant drop in hydraulic head due to groundwater pumping. Two thousand realizations are generated for each of the following parameters: hydraulic conductivity (K), compression index (C c), void ratio (e) and m (an empirical parameter relating hydraulic conductivity and void ratio). The correlation structure, the mean and the variance for each parameter were obtained from a literature review about field studies in the lacustrine sediments of Mexico City. The results indicate that among the parameters considered, random K has the largest effect on the ensemble average behavior of the system when compared to a nonlinear consolidation model with deterministic initial parameters. The deterministic solution underestimates the ensemble average of total settlement when initial K is random. In addition, random K leads to the largest variance (and therefore largest uncertainty) of total settlement, groundwater flux and time to reach steady-state conditions.

Investigation of the role of non-uniform suction flow in the performance of water-jet pump

Insufficient understanding of performance deviation between the uniform and non-uniform suction flows is a major problem encountered in the design and application of water-jet pumps. In this study, numerical investigation is conducted to illustrate the performance deviation and explain its generating mechanism. Steady simulations are performed to compare the pump performance with two different computational domains. One is a single water-jet pump under uniform inflow and the other is a complete water-jet propulsion system with non-uniform inflow. Results indicate that large non-uniformity of suction flow causes a substantial drop in the pump head. Flow details in the system are comprehensively discussed to describe the non-uniform inflow. Its primary feature is a distinct swirl distortion near the top which evolves into a circumferential vortex. Vortices and blade loadings are also explored. Consequently, the internal correlation between the non-uniform inflow and performance deviation is revealed. Due to non-uniform disturbances, a spanwise vortex shedding from the hub triggers a sharp downward peak of blade loading in the hub section. Moreover, a concentrated vortex deviates from the suction surface and induces an entire reduction in blade loading of the shroud section. These remarkable reductions in the blade loading eventually generate a head deviation.

Comprehensive Numerical Investigations of Unsteady Internal Flows and Cavitation Characteristics in Double‐Suction Centrifugal Pump

The RNG k‐ε turbulence model combined with cavitation model was used to simulate unsteady cavitating flows inside a double‐suction centrifugal pump under different flow rate conditions based on hexahedral structured grid. The numerical external characteristic performances agree well with the experimental performances. The predicted results show that the turbulence kinetic energy and the turbulence dissipation rate inside the impeller at design flow rate are lower than those at other off‐design flow rates, which are caused by various vortexes. Based on frequency‐domain analyses in the volute casing, the blade passing frequency is the dominant one of the pressure fluctuations except the vicinity of volute tongue for all operating cases, and the dominant frequency near the volute tongue ranges from 0 to 0.5 times the blade passing frequency for other off‐design points, while the blade passing one near the volute tongue is the dominant one of the pressure fluctuations at design point. The increase of flow rate reduces the pressure fluctuations amplitude. For cavitation cases, the blade loading of the middle streamline increases a bit during the initial stage, but, for serious cavitation, the blade loading near the blade inlet reduces to 0 and even negative values, and the serious cavitation bubbles block the blade channels, which results in a sharp drop in pump head. Under noncavitation condition, the predicted power related to the pressure in the impeller channels increases from the inlet to the exit, while, under different cavitation conditions at the design flow rate, these power‐transformation distributions in the impeller channels show that these power conversions are affected by the available NPSHa and the corresponding work in leading regions of the blades increases increases gradually a bit, and then it increases sharply in the middle regions, but it decreases in the blade trailing regions and is greatly influenced by secondary flows.

Pressure drop in pipelines due to pump trip event

We consider the pressure pulse or surge in a pipeline due to an unplanned sudden shutdown of a pump system in the pipeline network. This is known as water hammer. Our primary focus is the negative pressure pulse that travels downstream from the pump(s), is reflected with a sign reversal from the end, and travels back to the pump(s). As part of the preliminary design of a pipeline it is necessary to determine the minimum head envelope associated with such an event, which is used to determine where surge protection will be needed in the pipeline. Of particular interest is whether the initial head drop at the pump(s) due to a sudden drop of the flow speed to zero, as given by the Joukowski formula, gives a sufficiently accurate prediction of the minimum head at the pump(s). This minimum head is used to construct the minimum head envelope for the downstream pipeline. An examination of the relevant literature along with solution of the water hammer equations shows that, assuming the flow speed falls instantaneously to zero at the pump(s), the total drop in head at the pump(s) is given by the sum of the initial Joukowski head change and the friction loss under normal operating conditions. While the friction loss may not be significant in short pipelines, in long pipelines it cannot be neglected.

Efficacy of drainage trenches to stabilise deep slow landslides in clay slopes

The paper reports the results of a research aiming at the definition of innovative strategies to mitigate the risk generated by deep landsliding due to the slope-atmosphere interaction. The aim stems from the recognition of the connection between the accelerations of deep slow landslides and the seasonal fluctuations of the piezometric heads found to occur down to large depths in slopes, effect of seasonal cumulated rainfall infiltration, as verified in previous research studies for fissured clay slopes of the Italian southern Apennines. Given this slope behavior, the effects as stabilizing measure of systems of drainage trenches, from medium depth to deep, have been verified through the combination of finite element modeling of seepage and limit equilibrium analyses. The model results show that the trench system generates a ‘group effect’ on the piezometric heads at large depth, due to which the maximum drop in piezometric head occurs along the portion of maximum depth of spoon-shaped slip surfaces underlying the trench system. Hence, the reduction in piezometric head generated by the trench system makes such system an effective mitigation measure for deep landsliding. In the paper, the stabilizing effect of the trench system is also verified through its modeling for a deep landslide case history.