Ribbed Channel Research Articles

Contaminant dust effects on mist cooling in ribbed U-shaped channels of gas turbine blades

Mist cooling within turbine blades’ internal channels is a promising alternative to protect the blades from exceeding the temperature limit without additional coolant extraction. However, the presence of dust commonly encountered in harsh environments, such as deserts or sandstorms, can significantly affect cooling performance. This research employed numerical simulation methods and utilized the user defined function to direct the motion of mist/dust particles post-wall impact, to analyze the dust affected unsteady mist cooling effectiveness in a ribbed, U-shaped channel which is arranged within the blade to serve as a cooling passage. Additionally, this study examined the performance of mist cooling and heat transfer non-uniformity under various dust loading environments. The unsteady cooling mechanism of mist was discussed through the analysis of secondary flows induced by the inclined ribs and turning region. Enhanced cooling performance near the leading edge of the U-shaped channel was achieved by the coolant with mist under the action of a couple of vortices rotating in reverse. Moreover, this study revealed that dust particles exchanged heat with droplets and disrupted the flow fields, thereby altering the performance of mist cooling. These findings indicated that dust with smaller size, higher concentration, and greater specific heat significantly suppressed the mist cooling, but larger loading of dust led to an improvement in thermal uniformities within the channel.

Effects of Ribbed Crossflow Channel in a Turbine Blade on Film Cooling Performance of Diffusion Slot Holes with Various Cross Section Orientations

Abstract This paper investigates the influence of ribbed crossflow on the film cooling performance of a turbine rotor blade. A pressure-sensitive paint measurement technique was employed to measure the effectiveness of film cooling. The discharge coefficients were also measured to determine the flow resistance. A row of film holes was positioned at the pressure surface or suction surface with a spanwise hole spacing of 7.5D, which is half of the rib spacing. The experiments were carried out at a mainstream Reynolds number of 520,000, a turbulence intensity of 3.6%, and a density ratio of 0.97. The crossflow inlet velocity was 45% of the cascade inlet velocity. A fan-shaped hole with a 14 deg expansion angle (Fans-14), a horizontally oriented slot cross section diffusion hole with a 14 deg expansion angle (H1.7-14), and two vertically oriented slot cross section diffusion holes with 14 deg (V1.7-14) and 20 deg (V1.7-20) expansion angles were tested with/without crossflow. The results indicated that the slot cross-sectional orientation significantly changes the flow patterns inside the holes. H1.7-14 has stronger lateral expansion and better surface adhesion, while V1.7-14 and V1.7-20 yield more uniform lateral velocity distributions. Regardless of crossflow, H1.7-14 produces the highest film effectiveness and discharge coefficient on the pressure surface, while it changes to V1.7-20 on the suction surface. The ribbed crossflow increases the film effectiveness on both the pressure surface and suction surface, except for V1.7-20, as it is almost unaffected by the crossflow.

Effects of turning vane on flow control and heat transfer in ribbed two-pass channel with varied rib patterns

Faced with the escalating cooling requirements of turbine blades, two-pass channels with ribs on the internal surfaces have been extensively employed to enhance internal wall heat transfer. Considering the potential to mitigate flow separation and pressure losses generated by channel curvature, in this study, a computational fluid dynamics approach based on the realizable k-ε turbulence model is employed to explore the effects of turning vane introduction on the flow and heat transfer characteristics of two-pass channels with varying rib configurations. The rib configurations are identified as NN, NP, PP and PN. “N” denotes the ribs rotated 45° clockwise relative to the flow direction, while “P” denotes the ribs rotated 45° counterclockwise. The results indicate that the introduction of turning vanes improves the flow uniformity in the downstream channel of the two-pass channel with N-patterned upstream ribs, enhancing inter-rib heat transfer in the downstream channel. It also strengthens the heat transfer performance at the bend region of the two-pass channel with P-patterned upstream ribs. Furthermore, the introduction of turning vanes results in a decrease in friction loss factor for two-pass channels with various rib arrangements at varying levels of Reynolds numbers. The reduction is more pronounced in the two-pass channel featuring N-patterned upstream ribs, with a maximum decrease of 18.6 %. In contrast, the decrease is only 5.2 % in the PP-patterned rib channel. Additionally, the thermal performance factor of NP-patterned and NN-patterned rib channels increases by 8.5 % and 8.7 % respectively after the insertion of turning vanes. However, the enhancement is limited in the PP-patterned and PN-patterned rib channels.

Large eddy simulation of turbulent transport and thermal enhancement in a steam-cooled ribbed channel

Pulsating flow, as an active heat transfer enhancement technique, is expected to further improve thermal performance. To demonstrate the potential value of pulsating flow in blade cooling, a numerical investigation is conducted on the flow and heat transfer in a steam-cooled ribbed channel under steady and pulsating inflow at Re = 12000. LES, based on OpenFOAM-8, is employed and precursor simulation method is used to generate fully developed turbulent inflow. Three operating conditions, steady inflow (StF = 0), low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), are studied. The features under steady inflow condition (StF = 0) are firstly discussed, indicating that, due to the entry effect, the ribbed channel can be divided into two regions with different vortex motion behaviors. The ejections induced by vortex evolution enhance turbulent and energy transport between the sidewall and mainstream. Two cases of pulsating inflow are then carried out, finding that stronger ejections appear and low heat transfer area is significantly improved. Corresponding to low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), the Nusselt number has an increase of 3.511 % and 14.242 %, respectively, and friction factor has a rise of 3.934 % and 8.253 %, compared with steady inflow. The thermal performance factor is increased by 11.262 % at StF = 0.08, indicating better cooling performance than the rise of 2.188 % at StF = 0.02. It is suggested that pulsating flow with medium frequency pulsation has positive performance in a steam-cooled ribbed channel.

Investigation on the Flow and Heat Transfer Characteristics in a Multi-Pass Channel Using Magnetic Resonance Velocimetry and Transient Thermochromic Liquid Crystal

Abstract The three-dimensional flow field in multi-pass channels with and without ribs was measured by magnetic resonance velocimetry (MRV), while heat transfer performance on the endwall of channels in the same geometry was investigated using transient thermochromic liquid crystal (TLC) technique. The evolution of comprehensive three-dimensional flow field and their correlation with local heat transfer enhancement on end wall of multi-pass channels with and without ribs were revealed as a whole picture. Results show that the flow characteristics in the right-angle bend as well as the second pass are dramatically different for the smooth and ribbed channels, resulting in totally different features of heat transfer distribution on the end wall in those two channels. For the smooth channel, strong dean vortices form around the bend region near the outer wall where heat transfer is enhanced substantially. For the ribbed channel, no dean vortex but complex three-dimensional flow presents around bends. Heat transfer downstream of ribs close to the reattachment regions is strengthened noticeably. Comparison between velocity and heat transfer results suggest that one of the principle mechanisms driving heat transfer enhancement is both endwall directed velocity for smooth and ribbed channels, even though they are induced by different flow structures.

Effects of bidirectional rib arrangements on turbulent flow structure and heat transfer characteristics of a two-pass channel for turbine blade internal cooling

The thermal efficiency of gas turbine engines depends heavily on the cooling performance of the internal channels of turbine blades. In the present study, the effects of bidirectionally arranged ribs on the flow and heat transfer mechanism in a two-pass cooling channel are investigated numerically. The channel aspect ratio is kept constant at 1:2 (W: H), and the rib pitch-to-height ratio (P/e) is 10. Comparative analysis is performed for three different cross-sectioned (Square, triangular and Curved) ribs with Reynolds numbers ranging from 10,000-50,000. The results indicate that the bidirectional ribbed channel provided 69% better thermal performance compared to horizontal-only ribs due to its potential to induce secondary flow in both vertical and horizontal directions. The square and triangular ribs show similar characteristics, but the thermal performance of curved ribs drops by 11%. The pressure loss phenomenon is also lowest in the case of the curved ribs. The obtained Nusselt number and friction factor for all cases are normalized with the Dittus-Boelter correlation, Blasius correlation and the smooth channel. The detailed analysis of area-averaged normalized Nusselt number indicates that the best thermal performance occurs at the bend region due to the combined contributions of the ribs and the 180° turn. Furthermore, in terms of the overall thermohydraulic characteristics, the curved-bidirectional ribbed channel is noticed to have the best results with values of 1.38 and 1.25 for TEFo and TEFs respectively.

Secondary motions in turbulent ribbed channel flows

Secondary motions in turbulent ribbed channel flows

Numerical analysis of heat transfer characteristics in ribbed two-passed channel with varied cross section

The mid-chord region of turbine blades typically employs internal cooling channels to enhance heat transfer. However, traditional internal cooling channels are mostly designed in the form of straight channels, and studies based on it may not address the needs of variable cross section channels. Therefore, this study investigates the effect of rib configurations in variable cross section channels on channel performance. First, the cross sectional area of the two-passed channels is modified by altering the inclination angle of the dividers (−3°, 0°, and +3°). The flow pattern and heat transfer features within a two-passed channel with variable cross section under four different rib configurations of NP, NN, PN, and PP are investigated using numerical simulation. N denotes the ribs rotated 45° clockwise relative to the flow direction, while P denotes the ribs rotated 45° counterclockwise. Subsequently, the optimal rib configuration within the variable cross sectional two-passed channels is determined for Reynolds numbers ranging from 10 000 to 50 000. Results show that, at +3°, the PP exhibits the maximum decrease of up to 18.2% in transfer performance factor (TPF), while at −3°, the NN shows the maximum decrease of up to 12.7%. It is evident that the optimal rib configuration for two-passed channels under different divider inclinations is not consistent. At +3°, the NP exhibits the best TPF, while at −3°, the PP demonstrates the optimal TPF. This study provides insights into selecting appropriate rib configurations when the cross sectional area of internal channels within turbine blades varies. Compared to the studies that have focused on traditional straight channels, the research provides guidance for the design of ribbed two-passed channels with varied cross section.

Multi-Parameter Inversion Optimization for Transverse Rib Profile Enhanced Convective Heat Transfer

The convective heat transfer performance of the rib-element approach in the channel is influenced by the transverse rib profile. In present work, a nonlinear multi-parameter optimization method based on inversion optimization is proposed and further used to obtain the optimal rib profile in a rectangular channel. Firstly, four conventional profiles as the original ribbed channel were selected to obtain the convective heat transfer performance of the channel by experiment and numerical solution; secondly, several control points were selected along the profile, and the polar radius was updated, and curve fitting was carried out. The results show that the inversion optimization can optimize the rib profile to improve the convective heat transfer performance. As the number of control points increases, the optimized profile changes hardly. The inversion optimization yields a similar optimized profile regardless of the original rib profile. With the increase of original rib height, the enhanced heat transfer performance of optimized profile is better. For the ribbed channel with original height 0.4 × channel height, as the Reynolds number increases from 6000 to 33,000, the performance evaluation criteria of the optimized profile increase by 14.94% to 21.2% compared with the original triangular profile.

Effect of wall curvature on heat transfer and hydrodynamics in a ribbed cooling passage

Simplified rectangular ribbed cooling passages with a flat wall are extensively considered in exploring the internal cooling features of turbine blades, but the realistic blade has a twisted shape inherently. The effects induced by the curved wall have not been clarified in detail. In this work, adopting a verified v2f turbulence model, numerical investigations are completed to evaluate the effects of the curved wall on the internal cooling characteristics of a ribbed channel. Adopting the unified ribbed channel, flat, convex, and concave walls with distinct curvatures are comprehensively evaluated and compared in a wide Re range for the turbulent flow and heat transfer features as well as the flow and thermal performance. It is found that using the flat wall, ribs can typically induce recirculation vortices having a two-dimensional nature. In contrast, the curved wall significantly contributes to the counter-rotating vortex pairs on the spanwise plane. Combined with recirculation vortices offered by the ribs, the turbulent flow of the cooling channel with the curved wall has a remarkable three-dimensional feature. Hence, the turbulent activity and fluid mixing are enhanced greatly along with the raised heat transfer enhancement and friction loss. Particularly, the convex wall with a curvature of K = 4 provides 28.6 % higher heat transfer performance (Nu/Nu0) but 88.4 % higher resistance (f/f0) than the flat wall. Considering the overall cooling performance, the concave wall with a relatively small curvature is suggested with an improvement of up to 32.8 % concerning the factor (Nu/Nu0)/(f/f0) and 9.5 % on (Nu/Nu0)/(f/f0)1/3. Finally, it is highlighted that considering the effect of the wall curvature, the current study stimulates the mechanistic understanding and provides a design guideline for high-performance blade internal cooling.

Influence of Entrance Geometry and Thermal Boundary Conditions on Heat Transfer in a Rectangular Channel with 45 Deg Angled Ribs on One or Two Principal Walls

The purpose of this paper is to numerically investigate the influence of the entrance geometry and thermal boundary conditions on the local and averaged heat transfer coefficient in a ribbed rectangular channel with an aspect ratio of 5. Ribs, angled at 45°, were periodically deployed on one or two opposite sides, while the remaining walls of the rectangular channel were assumed to be smooth and unheated. The effect of entrance conditions was addressed by considering either a smooth or a ribbed unheated section upstream of the ribbed heated section. The effect of the thermal boundary condition was studied by considering a uniform heat flux imposed at the inter-rib region, or at the inter-rib and the rib baseplate, or at the whole interface between the ribbed surface and the coolant. Results, presented in the form of spatially resolved and spatially averaged Nusselt numbers, show that a ribbed section preceding the heated test section affects the heat transfer coefficient, relative to a smooth entrance section, for several repetitive modules. The influence of the thermal boundary condition was found to be mainly concentrated in the surface regions immediately upstream and downstream of each rib, with small differences, in terms of spatially averaged Nusselt numbers. The presented investigation is meant to point out that heat transfer experiments on ribbed channels, massively provided by the heat transfer community according to the current technical literature, should provide an exhaustive description of the entrance and thermal boundary conditions assumed in the experiments and eventually to discuss how they could potentially affect the results.

On the aero-thermal performance of flat-plate film cooling hole with variable rib heights

This study conducted a numerical investigation into the impact of different cooling air feeding methods and structural parameters of the internal ribbed crossflow channel on the performance of cylindrical film cooling holes under varying blowing ratios. The considered flow conditions encompassed two feeding methods (plenum or crossflow channel), three different rib heights (h = 2–8 mm), three internal crossflow directions relative to the mainstream (θ = 0°–180°), and four blowing ratios (M = 0.5–2.0). In the case of crossflow, the external crossflow had a Mach number of 0.3, and the internal crossflow's Reynolds number was set at 2 × 105. The study delves into flow analyses of the hole and external flow field, discharge coefficient characteristics, aerodynamic losses, and heat transfer characteristics. The findings reveal that the presence of internal crossflow significantly alters the flow field and performance compared to the coolant plenum case. However, the effects of crossflow are attenuated when internal turbulence rib structures are introduced, and this damping effect is further pronounced as the rib height increases. The aerodynamic and cooling characteristics of the hole progressively approach those of a plenum supply form, a phenomenon aptly termed the “Plenum effect” of the ribbed crossflow channel.

Impact of V-shaped interrupted ribs in cross-flow channels on film cooling

This study primarily investigates the enhanced heat transfer of V-shaped ribs with?in an internal cross-flow channel and their impact on external film cooling per?formance. The aim is to assess the advantages of V-shaped ribs in the cooling of gas turbine blades. The research specifically discusses the internal heat transfer efficiency of smooth channels, channels with V-shaped ribs, and channels with intermittently placed V-shaped ribs at a blowing ratio, M, of 0.5 and three different Reynolds numbers. The results indicate that the vortices generated by the coolant passing through the positive V-shaped ribs and intermittently placed V-shaped ribs effectively impinge on the upper and lower surfaces, thereby enhancing heat trans?fer performance. Regarding film cooling, under low Reynolds number conditions, the film cooling efficiency of the positive V-shaped ribs is 9-20% higher than that of the smooth channel. Under high Reynolds number conditions, the film cooling efficiency of the negative V-shaped ribs significantly increases, reaching 29-120%. The study demonstrates that rib shape and inlet Reynolds number have a signifi?cant impact on the swirl intensity of the coolant in the film cooling holes, and fluid with a certain swirl intensity exhibits better film cooling efficiency.

EXPERIMENTAL ANALYSIS OF HEAT TRANSFER AND THERMAL PERFORMANCE OF PARABOLIC TYPE SOLAR COLLECTOR WITH RIBBED SURFACE TEXTURE FOR CLEAN ENERGY EXTRACTION

This paper examines the performance of a parabolic type solar collector (PTSC) that uses both plain tube and ribbed surface textured tube channels for elevating the water temperature used for various applications. The performance of a solar water heater is evaluated experimentally. During the experiment, the solar radiation intensity and the feed water flow rate of 1.0 kg/min to 5.0 kg/min in steps of 1 kg/min are taken into consideration for analyzing the effect of ribbed textured tubes on the thermal effectiveness, frictional factor, convective transfer of heat, Reynolds number, and the Nusselt number of the PTSC. Furthermore, the overall performance of the PTSC is analyzed considering the above thermo-physical parameters. Based on the result of this study, at a flow rate of 3.0 kg/min, the thermal efficiency is found to be enhanced by about 28.25%, the friction factor is augmented by about 0.23%, the convective heat transfer coefficient is improved by 24.22%, and the Nusselt number is increased by about 26.32%. On average, an overall improvement in the performance of 8.25% is observed for the ribbed textured tube than that of the plain tube. The experimental error analysis shows that the standard deviation for both plain and ribbed textured tubes is in the range of 3.2, which is in the acceptable limit.

Вторичные течения Прандтля 2-го рода в пространственно-неравновесном турбулентном течении

In this work, a numerical study of turbulent flow and heat transfer in a plane channel was carried out. The features of secondary flows of Prandtl's 2nd kind, which arise in the vicinity of longitudinal ribs on the channel walls, are studied under conditions of spatial inhomogeneity of the flow. Simulations of four turbulent flows were carried out: flows in a smooth channel uniform in length, a uniform ribbed channel, as well as flows in a smooth and ribbed channel with an average velocity varying along the length. It is found that the presence of a rib in a homogeneous channel in the considered case significantly changes the distribution of turbulent flow characteristics over the channel section. These changes are due to the action of the emerging secondary flow with a maximum velocity of 5.2% of the average flow rate. In this case, changes in the velocity and thermal characteristics are similar. Both friction and heat transfer increase by about 10% due to the increased wetted surface area. The inhomogeneity of the flow, which is provided by the organization of blowing and suction through the upper wall of the channel, leads to more noticeable changes. In areas where the flow slows down, the fluid moves under conditions of an unfavorable pressure gradient. The intensity of turbulent pulsations in these places increases noticeably. In the presence of ribs, this leads to a significant increase in secondary flows. Both in the smooth and in the ribbed channel, an increase in the Reynolds analogy coefficient to a value of 1.07 was recorded, which is 6% higher than the uniform flow index. In general, based on the results of this work, we can conclude that the longitudinal ribbing is hardly capable of significantly changing the thermal-hydraulic properties of a flat surface in a turbulent flow, at least without taking special optimization measures. The spatial inhomogeneity of the flow, on the contrary, due to the different effects on the velocity and temperature profiles, has a certain potential for designing heat exchange devices with more suitable thermal-hydraulic properties.

Thermal-mechanical coupling analysis of the ribbed channels in regenerative cooling

Regenerative cooling plays a critical role in the thermal management for scramjet combustors, and the design of cooling channels is of utmost importance. To comprehensively analyze the performance of cooling channels, a validated thermal-mechanical coupling model was utilized in this study. The thermal and mechanical performance of both smooth and ribbed channels in regenerative cooling was investigated using Finite Volume Method and Finite Element Method. The findings indicate that the ribbed wall has a notable effect on enhancing the overall thermal performance of the channel. Moreover, the presence of ribs weakens the influence of buoyancy in the flow field, which can be one of the contributing factors in inhibiting heat transfer deterioration. Additionally, the design of ribs significantly reduces the average thermal stress experienced by the channel. However, it should be noted that the non-uniform heat transfer in the axial direction leads to a significant increase in local thermal stress. The triangular ribbed channel proves to be an effective approach in reducing thermal stress. Compared to rectangular ribbed ribs, the utilization of triangular ribs can result in a reduction of thermal stress by up to 30%. This observation highlights the advantage of triangular ribs in enhancing system life and safety by minimizing thermal stress.

Air Bubble Effect on Heat Transfer Enhancement in 90° Ribbed Parallel Channels Based on Photovoltaic-Thermal Collector Cooling

The effect of entrained air bubbles on heat transfer enhancement inside 90° ribbed parallel channels has been experimentally studied to improve electrical efficiency inside future solar panels. In this work, the Reynolds number was measured from 200 to 600. The essential ratios of channel aspect, rib height, and rib pitch were all set to 0.4, 0.18, and 10, respectively. The volumetric flow fraction for all test conditions varied from 0.0 to 0.5. The overall heat transfer distributions on the surface were captured using an infrared thermography camera. The main finding showed that the average heat transfer rate and the thermal performance gained beyond 25–81% and 7–82% compared with the smooth wall. In addition, the volumetric flow fraction of 0.5 at the Reynolds number of 200 became the best.

Numerical simulation and experimental investigation of heat transfer performance of turbine blade with ribbed channel

A combination of numerical simulation and experimental test is carried out, and the vortex core visualization technology is adopted to visualize vortex in the flow field and study the heat transfer mechanism. The heat transfer characteristics of air flow in 45° ribbed straight channel with aspect ratio of 1 and the other 6 new ribbed channels are studied. The results show that the average heat transfer performance of the new ribbed channel with all the fins 3.8 mm cut at the far end of fins along the flow direction is the best by comparing with the original ribbed straight channel under the same conditions. The average Nu, the average Nu/Nu0 and the average heat transfer enhancement factor FT of the ribbed wall is increased respectively by 25.1%, 24.8%, 22.7% on the average by comparing with the original ribbed channel. The experimental results show that the error between the experimental value and the simulated is about 10% for the outer wall temperature of ribbed channel.

Improving Gas Turbine Efficiency through Ribbed Channel Designs: A CFD-Based Study

Abstract: In order to increase performance and efficiency, this research article investigates the usage of ribbed channels in gas turbines. It uses computational fluid dynamics (CFD) simulations to assess various rib shapes and attack angles and evaluate the thermal-hydraulic performance of ribs. According to the results, square-shaped ribs consistently perform better than alternative rib geometries in terms of efficiency, normalized skin friction coefficient ratio, and skin friction coefficient ratio. The work emphasizes how crucial metal temperature prediction is in gas turbine blades and vanes because of the complex interaction between fluid dynamics and flow. The results may be used to establish and optimize cooling plans for increased gas turbine performance and efficiency

Numerical analysis and experiments on heat transfer and flow structures in rotating three-pass serpentine channels with ribs, guide vanes and trailing bleed holes

Numerical and experimental studies are conducted on heat transfer and pressure loss in a three-pass serpentine channel with trailing bleed holes. The guide vanes' effects in the smooth and ribbed channels are studied comparatively. Based on the hydraulic diameter and inlet velocity, the Reynolds number ranges from Re = 14,000 to Re = 100,000, and the rotation number ranges from Ro = 0 to Ro = 0.1. Through the numerical simulations, the rib configuration in serpentine channels influences the guide vane's flow control effects. Applying the guide vanes in the ribbed serpentine channel's tip bend region enhances the flow impingement and advection, increasing the total Nusselt number in the blade-tip region by about 25%, and this region's heat transfer uniformity is improved as well under non-rotating and rotating conditions without additional pressure loss penalty in the channel. Moreover, it is a promising method to improve the turning flow structures and enhance heat transfer further in the ribbed serpentine channel by applying the tandem guide vane in the tip bend region. Both the numerical computations and experiments show only slightly higher and more uniform heat transfer in the second and third passages after applying the guide vanes in the bend regions under non-rotating and rotating conditions. The experiments indicate that the rotation effects show a more appreciable influence on the heat transfer enhancement values along the serpentine channel than the channel Reynolds numbers. The heat transfer differences between the leading and trailing sides are 15.4%, 14.0%, and 21.3% in the three passages, respectively, at Re = 14,000 and Ro = 0.1, referring to the averaged Nusselt number in each passage. The CFD results demonstrate that the rotation significantly improves the heat transfer in the third passage by promoting more radial outflow through the tip hole, reducing the flow rates through the lateral bleed holes by about 13.2%.