Pressure Loss Coefficient Research Articles

Investigations on the unsteady flow mechanism of the high-throughflow fan with partial-height booster rotor

This paper describes the use of numerical simulations to evaluate the complicated steady and unsteady flow in a high-throughflow fan stage. A detailed investigation of the aerodynamic performance is carried out at the choking point, near-choking point, peak efficiency point, and near-stall point. The peak efficiency point is selected as a typical operating point to clarify the unsteady flow mechanism inside the fan stage. The unsteady simulation results show that the mass flow is lower under all operating conditions than in steady flow, and the difference increases as the operation point approaches the near-stall point. The isentropic efficiency decreases by 0.41% at the near-stall point, but improves slightly at the other points considered. The total pressure ratio does not change significantly. The total pressure loss coefficient of the stator increases significantly, but the changes in the isentropic efficiency of the fan stage mean that the stator has only a slight effect on the performance of the overall stage. An in-depth analysis of the peak efficiency point is conducted. First, the distribution of entropy along spanwise at the outlet of the rotor and stator domain is examined, and the unsteady effects are found to be mainly concentrated near the hub, mid-span, and higher-span of the stator. Detailed analysis of these three regions shows that the main influence comes from the distortion of the transmission of flow field information in the hub boundary layer at the rotor/stator interface, the interaction between the tip vortex and other vortexes near the mid-span region, and the interaction between the trailing edge separation vortex of the fan rotor and the surfaces of the stator.

Endwall-pulsed blowing of different excitation models to control flow separation on a highly-loaded compressor cascade

Abstract Endwall-pulsed blowing (EPB) is studied for three different excitation waveforms to improve the aerodynamic performance of highly loaded compressors. Some important excitation parameters include the excitation frequency and momentum coefficient, which were analyzed in detail. The results of the EPB are compared with the endwall steady blowing (ESB) case. For EPBs with the three excitation waveforms (Waveforms sine, triangle and trapezoid), excitation frequencies that are equal to an integral multiple of the natural frequency of the vortex shedding are optimal and provide better performances than the ESB with the same time-mean momentum coefficient. Moreover, the EPBs of the three excitation waveforms have significant differences in their aerodynamic performance improvements. The optimal case is achieved by the EPB with Waveform triangle and provides a total pressure loss coefficient with a reduction of 25.64%.

Effects of Pulsed Jet Intensities on the Performance of the S-Duct

The high curvature of modern S-ducts causes a strong secondary flow, which seriously affects the uniformity of the compressor inlet flow. In this study, the flow control method of a pulsed jet was applied in the S-duct at an incoming Mach number of 0.4. The jet holes were with an angle of 45° and were symmetrically distributed on the upper wall. Three jet intensities of 0.16%, 0.24%, and 0.31% were simulated using the unsteady Reynolds-averaged Navier–Stokes equations (URANS) and were validated by experiments. The mechanism of the pulsed jet, with respect to controlling the flow separation in the S-duct, was analyzed through secondary flow behaviors and boundary layer characteristics. The results indicated that the radial and axial pressure gradients were crucial to the formation of the large-scale vortices and reversed fluids in the S-duct. The pulsed jets were found to resist the adverse pressure gradient by exciting the turbulent kinetic energy of the boundary layer fluids. In addition, the dissipation process of vorticity was accelerated due to the promotion of the mixing effect by these devices. Moreover, in the current study, the area with high total pressure loss coefficients decreased gradually along with the intensity increase. Specifically, a maximum loss reduction of 5.9% was achieved when the pulse jet intensity was set to 0.31%, which means that the pulsed jet has great potential in controlling the flow separation in the S-duct.

Pressure Loss Coefficients of Ductwork Fitting Combinations With and Without Vanes (Baffles)

Abstract Ductwork components in ventilation systems are often installed in close proximity to each other due to space constraints. Published pressure loss coefficients are, however, only valid if there are sufficient distances between components. In this work, pressure losses of common combinations of two, three, and four bends and the addition of internal vanes were investigated with computational fluid dynamic simulations and validated with reference data. Pressure losses of combinations of bends without vanes were higher or lower than the sum of the single pressure losses of the components (combination effect), depending on the components and orientation. For bends with abrupt deflections, strong combination effects occurred; in some cases, pressure losses doubled. The spacing between the components was also a relevant factor. Combination effects were most pronounced for spacing lengths of the same order as the length of the flow separation region of the upstream bends. Consequently, certain spacer lengths were particularly unfavorable. Combination effects were found to be complex to predict and fluid simulations proved to be useful for analyzing the interactions. Adding vanes was found to be very useful. For bends and combinations with sharp deflections, the pressure loss coefficients were reduced by a factor of ten with vanes. Vanes also effectively reduced detrimental combination effects. The combination pressure losses with vanes were in all cases lower than the sum of the single components pressure losses. Pressure loss coefficients for combinations with vanes had a strong dependency on the Reynolds number. Furthermore, the downstream flow distributions were more homogeneous with vanes.

Aerodynamic Optimization and Mechanism Investigation on Performance Improvements in a Transonic Compressor Cascade

In this paper, a transonic compressor cascade was optimized to improve its aerodynamic performance. A new blade parameterization method with 16 control variables was first proposed to fit the shapes of the suction and the pressure side, as well as the leading edge. Then, the Kriging surrogate-model-based genetic algorithm (GA) was used to optimize the performance of the transonic cascade. The optimization algorithm is effective in reducing the total pressure loss while extending the working range of the cascade. The results show that the total pressure loss coefficient could be reduced by 11% at the best airflow angle and the working range could be extended by 6.9% for the optimized cascade in two-dimensional simulations. Similar improvement results could also be obtained in the simulations of their linear cascade cases. Detailed analyses show that the relative maximum thickness positions of the optimized blades move forward by about 10% to the leading edge, and the radii of curvature of the front half of the suction and pressure surfaces increase, compared with the initial blade. This makes the front half of the optimized blades look more closely like a wedge. Consequently, the passage shock strength is reduced and the shock changes from the passage normal shock to oblique shock. The weakened shock strength leads to the disappearance of the flow separation caused by the shock boundary layer interaction on the suction surfaces of the optimized blades, and results in a narrowed wake width at the outlet section.

Corner separation control in compressor stators with jets from the blade leading edge

Corner separation occurs easily in highly loaded compressor stators. This paper proposes a novel slot inside the stator blade, with the slot inlet located at the blade leading edge and the slot outlet located at the suction surface, by using the momentum of the incoming flow to form a high velocity jet to control the development of the boundary layer on the blade suction surface. For 3D compressor cascades, the influence of the key geometrical slot parameters on the flow fields in the slot and cascade passage and the aerodynamic performance of the cascade were investigated with a numerical method. Then, the stator blades in a highly loaded compressor stage were slotted to improve the flow in the stator blade passages. The main results can be summarized as follows. The use of slotted blades in the cascade effectively suppresses corner separation. When the cascade inlet velocity is high or the inlet flow is at a positive attack angle, the separation control effect improves. In the highly loaded compressor stage, slotted stator blades considerably reduced the flow loss at the stator corner, and the stage efficiency increased over the entire flow rate range. Furthermore, two cascades with unslotted and slotted blades were tested. The experimental and numerical results were consistent, demonstrating that the total pressure loss coefficient of a cascade can be effectively reduced by slotting the blades in the cascade.

Experimental investigation of intermediate compressor duct

The intermediate duct connects high-pressure and low-pressure compressors. It comprises flow channels and struts that fix the relative positions of the hub and shroud. The mechanism of airflow movement around the struts in the downstream intermediate ducts is experimentally investigated based on four cases, including two types of struts and two shapes of meridional flow channels. The measurement parameters of the intermediate duct under the same conditions are measured in the wind tunnel, including the total pressure loss coefficient at the outlet and axial wall pressure distribution. In addition, the flow characteristics near the wall are obtained through the oil flow test, and the frequency of the shedding vortex is captured by the dynamic pressure probes. The results demonstrate that the strut and channel with the modified profile can reduce the total pressure loss and eliminate wake oscillation by changing the flow characteristic. The total pressure losses of the modified profile at 0.2, 0.25, 0.3, 0.35, 0.4, and 0.45 Ma conditions are reduced by 60%, 63%, 83%, 89%, 85%, and 87%, respectively.

Impact of Slots on the Aerodynamic Performance of the Variable Inlet Guide Vane Cascade of a Centrifugal Compressor

This study reconstructed the flow field of a symmetrical variable inlet guide vane in a centrifugal compressor through the passive control method of vane slots. Based on the high-fidelity numerical simulation model verified by experiments, the influence of different slot forms on the flow field was investigated, and the passive control mechanism was revealed. The results demonstrated that the vane slot method can effectively suppress the suction surface separation and broaden the range of low-loss incidence angles. Overall, the 50_30 slotted vane achieves the best flow field control, with a 65.6% reduction in the total pressure loss coefficient and a 2.3° reduction in the deviation angle, respectively, at a 25° incidence angle. The linear characteristics of the pre-swirl grade variation curve with variable inlet guide vane incidence angles are also improved. Furthermore, changing the slot outlet angle has the most significant influence on the aerodynamic performance as it changes the throat width of the location, thereby affecting the flow rate and momentum of the jet. Finally, the impact of the velocity varies in the first self-similarity region on the slotted vane. The results indicate that, in contrast to the baseline vane, the suppression effect of the slot jet on the flow separation improves with the inlet velocity, whereas the deviation angle of the slotted vane declines with the inlet velocity. Meanwhile, the higher the incoming flow velocity, the better the slotted jet can inhibition of flow separation.

Effect of Slot Jet Flow on Non-Axisymmetric Endwall Cooling Performance of High-Load Turbines

As vane inlet temperatures and turbine loadings are increasing, the aerodynamic and thermal management for the endwalls of gas turbines have received increased attention. Non-axisymmetric endwalls are becoming popular due to their proficient capabilities to modify the secondary flow fields and to change the film cooling performance on the endwalls. In this study, by considering the interaction between mainstream and purge flow based on non-axisymmetric endwall contouring, the numerical research model used in the present research was established. Based on the validated numerical method, the influence of the non-axisymmetric endwall contouring on the film-cooling effectiveness and aerodynamic characteristics was studied. Furthermore, the effect of different inclination angles on the film-cooling performance of the contoured endwalls was also investigated. The results indicate that for the high-load turbine vane used in this research, various types of non-axisymmetric endwall contouring can alter the aero-dynamic characteristics and cooling performance simultaneously. By inhibiting the secondary flows, non-axisymmetric endwall contouring can reduce the total cascade pressure loss coefficient by 0.305%. In addition, non-axisymmetric endwall contouring can significantly enhance the effective coverage area of purge flow up to 28.29%, and the endwall near the suction side can achieve better cooling performance. Finally, non-axisymmetric endwall contouring can improve the protective effect of large-angle purge flow.

Cooling performance of a teardrop cross-section Kagome truss-filled array jet impingement composite cooling structure

The target surface is coupled to truss rods and the jet space to form a robust overall structure using 30 Kagome truss cores with 5 × 6 array configurations. This paper focuses on the cooling performances of the array jet impingement structure with the Kagome truss array in a 3D printing heat exchanger at Reynolds numbers (Re) ranging from 5000 to 50,000. The cooling characteristics of the Kagome truss-filled array jet impingement with a circular cross-section (CC) and a teardrop cross-section (TC) are comparatively studied through experiments and numerical simulations. The effects of the truss array arrangements, the diameter of the cross-section (d) and the trailing edge angle (α) on the cooling characteristics are studied by numerical simulation in the TC, where the truss array arrangements include an in-line arrangement and a staggered arrangement, d = 1–3mm and α = 45°–90°. The results indicate that when d is 3 mm and α is 45°, the TC has better cooling performance compared to the CC. The TC in the staggered arrangement has a smaller pressure loss coefficient (Cp), while that in the in-line arrangement has a higher average Nusselt number on the impingement target surface (Nuave). The comprehensive thermal factor (F) is increased by 6.58%–21.00% with the increase in d from 1 mm to 3 mm and decreased by 7.16%–8.90% with the increase in α from 45° to 90° in the TC. Two empirical correlations for the Nuave and the Cp for the TC have an accuracy of about 5%.

Effect of protrusion shape on film cooling performance for the cylindrical hole embedded in a contoured crater

The cratered film-cooling hole is regarded as one of the potential applications with high cooling performance and low cost. This study focuses on the influence of the protrusion shape for the contoured crater embedded in the cylindrical hole. Four protrusion shapes, i.e., arc, rectangle, trapezoid, and triangle, are considered. The cooling effectiveness, flow structure, and aerodynamic loss for the cratered holes at blowing ratios of 0.5-2.5 are obtained using the numerical method with the shear stress turbulence model. The numerical results indicate that the arc and triangle protrusion models provide better lateral coolant coverage and higher area-averaged cooling effectiveness at higher blowing ratios, attributed to the ascendant anti-kidney-shaped vortex pair. The rectangle protrusion model provides the lowest area-averaged cooling effectiveness because the kidney-shaped vortex pair dominates the downstream flow field. For the aerodynamic loss, the largest total pressure loss coefficient occurs for the rectangle protrusion model and nearly equivalent values for the other three protrusion models. The contoured cratered holes with arc and triangle protrusions are generally recommended.

Computational Modelling to Predict the Pressure Loss Coefficient of Pipe Fitting at KKTDI

Water pipeline system has an important role in delivering water throughout the whole community using piping system. Anyleakages or damages in any part of the water pipeline system will not only cause problem in delivering water but also could cause cost damage and affect the daily life of the community. The main objective of this research is to investigate the flow characteristics in the pipeline at Kolej Kediaman Tun Dr. Ismail (KKTDI) and to investigate the pressure drop due effect due to leakage along the pipeline system. The second objective is to assess the CFD approaches to calculate the pressure loss coefficients. Computational Fluid Modelling (CFD) simulations used to predict the flow variables such as velocity, pressure by solving the mathematical equations describing the relationship between the flow variables. This program is used in this research to determine the pressure loss coefficients using simulations. The pressure loss coefficient of the piping system is around 33.8 to 50.4 while the average pressure loss coefficient of the plotted graph is 13.1. In conclusion, the pipeline system of KKTDI residential college is studied carefully to determine the pressure loss coefficient and the objective is achieved.

Computational Fluid Dynamics Analysis of Blood Flow Changes during the Growth of Saccular Abdominal Aortic Aneurysm.

Computational fluid dynamics analysis of the growth process of saccular abdominal aortic aneurysm was performed. A 3D model of aortic aneurysm was created based on CT images. Properties in terms of wall shear stress, mean flow velocity, mean pressure, energy loss, and pressure loss coefficient were calculated using thermal fluid analysis software "ANSYS CFX." As the aneurysm expanded, the mean flow velocity decreased and the wall shear stress, mean pressure, energy loss, and pressure loss coefficient increased. Wall shear stress increased when the aneurysm was small, suggesting that is related to the development and growth of the aneurysm. (This is secondary publication from J Jpn Coll Angiol 2021; 61: 3-10.).

Experimental study on the aerodynamic performance of variable geometry low-pressure turbine adjustable guide vanes

An annular cascade testing rig of a variable-geometry low-pressure turbine with a large expansion angle was designed and built, combining a five-hole probe, a surface static pressure test system, and a PIV(Particle Image Velocimetry) measurement system. The effects of exit Mach numbers (0.2, 0.3, 0.4), turning angles (−1.5°, 0°, 3°), and adjustable device diameters (30 mm, 40 mm) on turbine cascade aerodynamic performance were experimentally investigated. Numerical simulations were also carried out to gain more insight into the flow fundamentals. Results show that the endwall clearance and the adjustable device significantly influence the flow field, with leakage flows before, after, and around the disc. The leakage vortex and passage vortex formation resulted in two high-loss regions in the shroud and hub endwall regions. The aerodynamic loss structures at the exit section were similar at different Mach numbers and varied considerably at different turning angles. Besides, a larger area of the adjustable device (d = 40 mm) was found to reduce the leakage loss caused by upper and lower clearance leakage flows and inhibit the development of secondary flows, resulting in a more straightforward secondary flow structure and a smaller influence range. Quantitatively, the adjustable device with a diameter of 40 mm could decrease the average total pressure loss coefficients by 11.5%, 16.6%, and 6.3% at three turning angles (−1.5°, 0°, 3°), respectively, compare to the adjustable device with a diameter of 30 mm.

Surrogate modeling of pressure loss & mass transfer in membrane channels via coupling of computational fluid dynamics and machine learning

Spacers are integral to the operation of membrane systems for both structural purposes and improving mass transfer dynamics that drive water permeation at the cost of increased pressure losses. 321 computational fluid dynamics (CFD) simulations were performed to provide high-fidelity data on hydrodynamic and mass transport behavior of spacer-filled membrane channels. CFD simulations were used to investigate the impact of the geometric parameters of spacers on pressure loss and concentration polarization in membrane channels. Spacer designs were characterized using six parameters that were varied in simulations to sample the domain of commercially available designs. Machine learning models were trained on CFD data to produce surrogate models for predicting pressure loss and mass transfer coefficients. These surrogate models consider more geometric parameters than existing empirical equations resulting in more representative and flexible models that can be integrated into existing module-scale or system-scale modeling software. Surrogate models were coupled with a particle swarm optimization algorithm and found that spacer designs with a diameter of 0.3 mm, length of 3.6 mm, angle between 42 and 46°, and moderate diameter necking (~60 %) best balances the trade-off between reduced concentration polarization and increased pressure losses in membrane channels with channel velocities between 0.05 and 0.35 m/s.

CFD analysis of flow control in compressor cascade using MVGs

Abstract The present study reports the numerical investigation of the compressor cascade. To minimize the separation phenomenon in the compressor cascade, a passive flow control device i.e. Micro Vortex Generator (MVG) is utilized. MVG is a very simple and lightweight attachment mounted infront of the leading edge of the cascade blade. Due to being passive in nature, it neither consumes power nor requires any external device to actuate. The numerical simulations were carried out on a highly loaded compressor cascade at an angle of incidence of −1° under subsonic conditions at Mach number 0.2. The profile of the compressor cascade blade was double circular arc (DCA), unsymmetrical and cambered at 40°. Two different types of micro vortex generators were mounted infront of the leading edge in the compressor cascade to control the secondary flows since secondary flows were responsible for various losses in cascade. To analyze the flow under incompressoible state of air (M = 0.2), Star CCM + software has been used. To simulate the flow under turbulent condition, k-ω SST turbulence model was used. A velocity profile of 25 mm boundary layer thickness was extracted and used as an input in the compressor cascade. Mounting of MVG on compressor cascade enhanced drag but also increased lift. Total pressure loss coefficient (TPLC) was calculated to compare the losses. The aerodynamic efficiency in terms of coefficient of lift and coefficient of drag has been used to study the effect of MVG over cascade. It is found that there is reduction in total pressure loss coefficient (TPLC) for trapezoidal and curved trapezoidal types of MVGs and the decrease in percentage are 2.17 and 8.86%, respectively. Alos, aerodynamic efficiency is increased by mounting trapezoidal and curved trapezoidal types of MVG and the increase in percentages are 2.03 and 3.10%, respectively.

Numerical investigation on the Thermal-hydraulic performance of the modified channel supercritical CO2 printed circuit heat exchanger

Printed circuit heat exchangers (PCHE) are designed to improve heat recovery and energy saving in supercritical CO2 (S-CO2) power cycles. In the current study, a modified channel PCHE is proposed based on the regular straight channel and a zigzag channel. The thermal–hydraulic performance of four different types of PCHE is numerically investigated and the methods are verified by both experimental and numerical results. The numerical results are presented for a Reynolds number based on the inlet conditions between 5 000 and 25 000. From the numerical results, the local pressure loss and local heat transfer coefficients are analyzed and discussed. Subsequently, the global Nusselt number and Fanning friction coefficients are discussed. It is found that the inserted straight section contributes to uniform flow, resulted in significant pressure loss reduction with a slight decrease in heat transfer. The modified channel can reduce the Fanning friction coefficient by 33.1%-84.7% while the global Nusselt number reduction is about 3.6%-30.3%. This leads to a maximum performance evaluation criterion (PEC) enhancement of 45.9%.

Similarity solution of subcritical pressure discharges from vessels for arbitrary gases

Based on the Bernoulli’s equation Fischer and Boettcher (2021) developed a model to predict the transient gas discharge from a vessel. Their dimensionless number was able to capture a variation of the molar mass, temperature, vessel volume and opening diameter and showed constant values for these. The influence of the gas, though, could not be completely captured. In this work we improve the model by optimizing the pressure loss coefficient, modifying the dimensionless number and solving the differential equation for determining the pressure over time using the 4th-order Runge-Kutta method. The model was extended to include the influence of the ambient pressure. These improvements lead to the first similarity correlation valid for arbitrary gases. Multiple numerical simulations are performed with ANSYS CFX to verify the similarity model. A grid independence study showed differences below 1 %. The mean deviation between the numerical simulation and the similarity-model is 1.939 %.

Pressure Losses Downstream of a Compact Valve in the Inlet Chamber of an Intermediate-Pressure Steam Turbine

Deep knowledge about pressure and energy losses in each part of a steam turbine is crucial for assuring the required efficiency and operational reliability. This paper presents the experimental as well as the numerical study of pressure losses in the inlet chamber of an intermediate-pressure steam turbine. Measurements were carried out on a complex model, where not only was there an inlet turbine chamber, but also a compact valve assembly situated upstream and nozzles situated downstream. The compact valve as well as the turbine inlet chamber were relatively small. Therefore, greater pressure losses were expected. The aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences was responsible for acquiring the measurements, which were carried out in a modular in-draft wind tunnel. In order to learn further details, numerical simulations were carried out. Doosan Skoda Power was responsible for this. A package of ANSYS software tools was used. Measured data were described and compared with numerical ones. Pressure losses were generalized in the form of the total pressure loss coefficient. As a result, pressure losses in similar turbine compact inlet chambers can be predicted with the required accuracy.

Hydraulic design optimization of spherical header for future fast reactors of India

The liquid sodium as coolant in a typical pool type Liquid Metal cooled Fast Breeder Reactor (LMFBR), flows through primary sodium pump, spherical header and finally enters the grid plate, which acts as an inlet plenum to heat-generating sub-assemblies. The reduction of pressure drop in primary circuit would reduce the operating cost of the system. Spherical header, a vital component in primary circuit suffers major flow non-uniformities resulting in higher pressure drop. Reduction of the pressure drop by uniformization of sodium flow in spherical header is considered. To this end, a 3D computational fluid dynamics (CFD) analysis is carried out to investigate the hydrodynamics of flow, inside the spherical header. Towards this a relationship between pressure loss coefficient and geometrical dimensions, viz., diameter and height of the cone, inside the header are established in order to minimize the pressure drop. The variation of pressure loss coefficient is estimated for header without and with the internals. The static pressure loss coefficient inside the spherical header without an internal cone is found to be 5.59. With a suitable and optimized geometrical dimension of the cone as internal flow guiding device, the loss coefficient is reduced to 0.53. The loss coefficient predicted for the spherical header is validated against the experimental estimates. Consequently, the simplified design of the flow guiding device is achieved by removing baffles.