Pressure Losses for Jet Array Impingement With Crossflow

2012 ◽  
Author(s):  
Yeshayahou Levy ◽  
Arvind G. Rao ◽  
V. Erenburg ◽  
V. Sherbaum ◽  
I. Gaissinski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Numerical Simulations ◽  
Gas Turbines ◽  
Total Pressure ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Solar Panels ◽  
Cfd Simulations ◽  
Pressure Losses

Jet impingement is an efficient heat transfer method and has been used successfully in cooling of turbine blades in gas turbine engines. Although many studies have been conducted on the heat transfer characteristics of jet impingement array, there is a lack of knowledge in pressure drop characteristics of large jet impingement arrays. The pressure losses encountered are becoming increasingly important when applied to micro gas turbines, cooling concentrated solar panels and high density electronic chips. The present work focuses on experimental and theoretical investigation of pressure losses in low Re impingement arrays, 200< Re <3000. Experiments were carried out on jet impingement array with nozzle diameters of 200 to 800 μm. Numerical simulations were also performed with available commercial CFD tools. Reasonable comparisons between experimental results and numerical simulations were obtained. Detailed flow structure, mass flow rate distribution, jet velocity profiles, and pressure drop within the array in the streamwise direction were obtained from the CFD simulations. These simulations enhance the understanding of the physics within multiple jet impingement system. Additionally a semi empirical–analytical method is developed for calculating the total pressure loss within a multi jet impingement system. This simple methodology can provide a quick estimate of the total pressure drop and hence is suited for first order optimization. The methodology is validated by results obtained from experiments and from CFD simulations.

Experimental Investigation of Crossflow Diverters in Jet Impingement Cooling

2019 ◽  
Author(s):  
Srivatsan Madhavan ◽  
Kishore Ranganath Ramakrishnan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Target Surface ◽  
Pumping Power ◽  
Detailed Measurement ◽  
To Come

Abstract Jet impingement is a cooling technique commonly employed in combustor liner cooling and high-pressure gas turbine blades. However, jets from upstream impingement holes reduce the effectiveness of downstream jets due to jet deflection in the direction of crossflow. In order to avoid this phenomenon and provide an enhanced cooling on the target surface, we have attempted to come up with a novel design called “crossflow diverters”. Crossflow diverters are U-shaped ribs that are placed between jets in the crossflow direction (under maximum crossflow condition). In this study, the baseline case is jet impingement onto a smooth surface with 10 rows of jet impingement holes, jet-to-jet spacing of X/D = Y/D = 6 and jet-to-target spacing of Z/D = 2. Crossflow diverters with thickness ‘t’ of 1.5875 mm, height ‘h’ of 2D placed in the streamwise direction at a distance of X = 2D from center of the jet have been investigated experimentally. Transient liquid crystal thermography technique has been used to obtain detailed measurement of heat transfer coefficient for four jet diameter based Reynolds numbers of 3500, 5000, 7500, 12000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. However, this comes at the expense of increase in pumping power. Pressure drop for the enhanced geometry is 1–1.5 times the pressure drop for baseline impingement case. At a constant pumping power, crossflow diverters produce 9–15% enhancement in heat transfer coefficient as compared to baseline smooth case.

Advanced Rayleigh Pressure Loss Model for High-Swirl Combustion in a Rotating Combustion Chamber

2015 ◽  
Author(s):  
Andreas Penkner ◽  
Peter Jeschke
Keyword(s):  
Heat Transfer ◽  
Combustion Chamber ◽  
Dynamic Model ◽  
Gas Turbines ◽  
Total Pressure ◽  
Fluid Flows ◽  
Pressure Losses ◽  
Gas Dynamic ◽  
Swirl Combustion ◽  
Transfer Problems

This paper considers the effect of excessive total pressure losses for heat transfer problems in fluid flows with a high circumferential swirl component. At RWTH Aachen University, a novel gas generator concept is under research. This design avoids some disadvantages of small gas turbines and uses a rotating combustion chamber. During the pre-design of the rotating combustion chamber using CFD tools, unexpected high total pressure losses were detected. To analyze this unknown phenomenon, a gas-dynamic model of the rotating combustion chamber has been developed to explain the unexpected high Rayleigh pressure losses. The derivation of the gas-dynamic model, the physical phenomenon related to the high total pressure losses in high-swirl combustion, the influencing factors, as well as thermodynamic interpretation of the Rayleigh pressure losses, are presented in this paper. In addition, the CFD results are validated by the gas-dynamic model derived. The results presented here are of possible interest for a wide range of applications, since these fundamental findings can be transferred to all heat transfer problems in fluid flows with a high circumferential swirl component.

Conjugate Heat Transfer Characteristics of Double Wall Cooling With Gradient Diameter of Film and Impingement Holes

2021 ◽  
Author(s):  
Juan He ◽  
Qinghua Deng ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Total Pressure ◽  
Flow Direction ◽  
Turbine Blades ◽  
Total Pressure Loss ◽  
Advanced Technique ◽  
Cooling Effectiveness ◽  
Uniform Pattern ◽  
Double Wall

Abstract Double wall cooling, consisting of internal impingement cooling and external film cooling, is believed to be the most advanced technique in modern turbine blades cooling. In this paper, to improve the uniformity of temperature distribution, a flat plate double wall cooling model with gradient diameter of film and impingement holes was proposed, and the heat transfer and flow characteristics were investigated by solving steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with SST k-ω turbulence model. The influence of gradient diameter on overall cooling effectiveness and total pressure loss was studied by comparing with the uniform pattern at the blowing ratios ranging from 0.5 to 2. For gradient diameter of film hole patterns, results show that −10% film pattern always has the lowest film flow non-uniformity coefficient. The laterally averaged overall cooling effectiveness of uniform pattern lies between that of +10% and −10% film patterns, but the intersection of three patterns moves upstream from the middle of flow direction with the increase of blowing ratio. Therefore, the −10% film pattern exerts the highest area averaged cooling effectiveness, which is improved by up to 1.6% and 1% at BR = 0.5 and 1 respectively compared with a uniform pattern. However, at higher blowing ratios, the +10% film pattern maintains higher cooling effectiveness and lower total pressure loss. For gradient diameter of impingement hole patterns, the intersection of laterally averaged overall cooling effectiveness in three patterns is located near the middle of flow direction under all blowing ratios. The uniform pattern has the highest area averaged cooling effectiveness and the smallest non-uniform coefficient, but the −10% jet pattern has advantages of reducing pressure loss, especially in the laminated loss.

Optimal Position of Rectangular Vortex Generator for Heat Transfer Enhancement in a Flat-Plate Channel

2017 ◽  
Author(s):  
Tariq Amin Khan ◽  
Wei Li ◽  
Zhengjiang Zhang ◽  
Jincai Du ◽  
Sadiq Amin Khan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Numerical Simulations ◽  
Flat Plate ◽  
Heat Transfer Enhancement ◽  
Angle Of Attack ◽  
Vortex Generator ◽  
Transfer Enhancement ◽  
Optimal Position ◽  
Plate Channel

Heat transfer is a naturally occurring phenomenon which can be greatly enhanced by introducing longitudinal vortex generators (VGs). As the longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty, VGs are widely used to enhance the heat transfer of flat-plate type heat exchangers. However, there are few researches which deal with its thermal optimization. Three dimensional numerical simulations are performed to study the effect of angle of attack and attach angle (angle between VG and wall) of vortex generator on the fluid flow and heat transfer characteristics of a flat-plate channel. The flow is assumed as steady state, incompressible and laminar within the range of studied Reynolds numbers (Re = 380, 760, 1140). In the present work, the average and local Nusselt number and pressure drop are investigated for Rectangular vortex generator (RVG) with varying angle of attack and attach angle. The numerical results indicate that the heat transfer and pressure drop increases with increasing the angle of attack to a certain range and then decreases with increasing angle of attack. Moreover, the attach angle also plays an importance role; a 90° attach angle is not necessary for enhancing the heat transfer. Usually, heat transfer enhancement is achieved at the expense of pressure drop penalty. To find the optimal position of vortex generator to obtain maximum heat transfer and minimum pressure drop, the data obtained from numerical simulations are used to train a BRANN (Bayesian-regularized artificial neural network). This in turn is used to drive multi-objective genetic algorithm (MOGA) to find the optimal parameters of VGs in the form of Pareto front. The optimal values of these parameters are finally presented.

Shellside Waterflow Pressure Drop Distribution Measurements in an Industrial-Sized Test Heat Exchanger

1988 ◽  
Vol 110 (1) ◽  
pp. 60-67 ◽  
Author(s):  
H. Halle ◽  
J. M. Chenoweth ◽  
M. W. Wambsganss
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Operating Cost ◽  
Power Requirement ◽  
Pressure Drops ◽  
Pressure Losses ◽  
Finned Tubes ◽  
Heat Exchanger Design ◽  
Isothermal Water

Throughout the life of a heat exchanger, a significant part of the operating cost arises from pumping the heat transfer fluids through and past the tubes. The pumping power requirement is continuous and depends directly upon the magnitude of the pressure losses. Thus, in order to select an optimum heat exchanger design, it is is as important to be able to predict pressure drop accurately as it is to predict heat transfer. This paper presents experimental measurements of the shellside pressure drop for 24 different segmentally baffled bundle configurations in a 0.6-m (24-in.) diameter by 3.7-m (12-ft) long shell with single inlet and outlet nozzles. Both plain and finned tubes, nominally 19-mm (0.75-in.) outside diameter, were arranged on equilateral triangular, square, rotated triangular, and rotated square tube layouts with a tube pitch-to-diameter ratio of 1.25. Isothermal water tests for a range of Reynolds numbers from 7000 to 100,000 were run to measure overall as well as incremental pressure drops across sections of the exchanger. The experimental results are given and correlated with a pressure drop versus flowrate relationship.

Prediction and Measurement of the Flow and Heat Transfer Along the Endwall and Within an Inlet Vane Passage

2002 ◽  
Author(s):  
Hugo D. Pasinato ◽  
Zan Liu ◽  
Ramendra P. Roy ◽  
W. Jeffrey Howe ◽  
Kyle D. Squires
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Numerical Simulations ◽  
Total Pressure ◽  
Solid Surfaces ◽  
Air Injection ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Reynolds Analogy

Numerical simulations and laboratory measurements are performed to study the flow field and heat transfer in a linear cascade of turbine vanes. The vanes are scaled-up versions of a turbine engine inlet vane but simplified in that they are untwisted and follow the mid-span airfoil shape of the engine vane. The hub endwall is axially profiled while the tip endwall is flat. The hub endwall comprises the focus of the heat transfer investigation. Configurations are considered with and without air injection through three discrete angled (25 degrees to the main flow direction) slots upstream of each vane. The freestream turbulence intensity at the vane cascade inlet plane is 11 (± 2) percent, as measured by a single hot-wire placed perpendicular to the mean flow. The transient thermochromic liquid crystal technique is used to measure the convective heat transfer coefficient at the hub endwall for the baseline case (without air injection through the slots), and the heat transfer coefficient and cooling effectiveness at the same endwall for the cases with air injection at two blowing ratios. Miniature Kiel probes are used to measure the distribution of total pressure upstream of, within, and downstream of one vane passage. Numerical simulations are performed of the incompressible flow using unstructured grids. Hybrid meshes comprised of prisms near solid surfaces and tetrahedra away from the wall are used to resolve the solutions, with mesh refinement up to approximately 2 million cells. For all calculations, the first grid point is within one viscous unit of solid surfaces. A Boussinesq approximation is invoked to model the turbulent Reynolds stresses, with the turbulent eddy viscosity obtained from the Spalart-Allmaras one-equation model. The turbulent heat flux is modeled via Reynolds analogy and a constant turbulent Prandtl number of 0.9. The simulations show that endwall axial profiling results in flow reversal upstream of the vane, an effect that lowers the Stanton number for the baseline flow near the vane leading edge compared to our previous work in a flat-endwall geometry. Predictions of the total pressure loss coefficient show that the peak levels are higher than those measured.

Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing

2019 ◽  
Author(s):  
Shinjan Ghosh ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Blade Cooling

Abstract Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.

Numerical Investigation of Heat Transfer and Pressure Drop Characteristics for Different Hole Geometries of a Turbine Casing Impingement Cooling System

2011 ◽  
Author(s):  
F. Ben Ahmed ◽  
R. Tucholke ◽  
B. Weigand ◽  
K. Meier
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cooling System ◽  
Ambient Air ◽  
Impinging Jets ◽  
Nozzle Geometry ◽  
Impingement Cooling ◽  
Pressure Losses ◽  
Aspect Ratios ◽  
Mach Numbers

A representative part of an active clearance control system for a low pressure turbine has been numerically investigated. The setup consisted of a cylindrical plenum with 20 inline arranged impinging jets at the bottom side discharging on a flat plate. The study focused on the influence of the nozzle geometry on the flow as well as heat transfer characteristics at the impingement plate and the discharge pressure drop. CFD (Computational Fluid Dynamics) simulations were performed for a constant Reynolds number ReD = 7,500 and different mean jet Mach numbers up to 0.7. Different length-to-diameter ratios of the jet holes (L/D) and various hole shapes (cylindrical, elliptic, convergent and divergent conical) were investigated to evaluate the performance of the impingement cooling configurations. The predictions showed a significant influence of the length-to-diameter ratio of the orifice bores on the heat transfer and the pressure losses. For L/D = 2 no suction of the ambient air in the nozzles was observed. In comparison to the configuration with L/D = 0.25 an improvement of the discharge coefficient of 9% for Ma = 0.7 and 20% for Ma = 0.17 was achieved. However, the highest heat transfer was observed for the smallest L/D-ratio of 0.25. The shape variation showed that only the elliptic jet holes with a ratio of AR = 0.5 enhanced the overall heat transfer and simultaneously reduced the pressure losses because of discharging onto the target plate. This result was found to be valid for all investigated jet Mach numbers. Additionally, for both elliptic jet aspect ratios of 0.5 and 2 the axis-switchover phenomenon of the flow was observed.

Isolated and Coupled Effects of Rotating and Buoyancy Number on Heat Transfer and Pressure Drop in a Rotating Two-Pass Parallelogram Channel With Transverse Ribs

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Tong-Miin Liou ◽  
Shyy Woei Chang ◽  
Yi-An Lan ◽  
Shu-Po Chan
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Cross Sectional ◽  
Gas Turbine Blades ◽  
Performance Factors ◽  
Heat Transfer Efficiency ◽  
Rotating Channel

Detailed Nusselt number (Nu) distributions over the leading (LE) and trailing (TE) endwalls and the pressure drop coefficients (f) of a rotating transverse-ribbed two-pass parallelogram channel were measured. The impacts of Reynolds (Re), rotation (Ro), and buoyancy (Bu) numbers upon local and regionally averaged Nu over the endwall of two ribbed legs and the turn are explored for Re = 5000–20,000, Ro = 0–0.3, and Bu = 0.0015–0.122. The present work aims to study the combined buoyancy and Coriolis effects on thermal performances as the first attempt. A set of selected experimental data illustrates the isolated and interdependent Ro and Bu influences upon Nu with the impacts of Re and Ro on f disclosed. Moreover, thermal performance factors (TPF) for the tested channel are evaluated and compared with those collected from the channels with different cross-sectional shapes and endwall configurations to enlighten the relative heat transfer efficiency under rotating condition. Empirical Nu and f correlations are acquired to govern the entire Nu and f data generated. These correlations allow one to evaluate both isolated and combined Re, Ro and/or Bu impacts upon the thermal performances of the present rotating channel for internal cooling of gas turbine blades.

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