Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part I: Numerical Method

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Tom Verstraete ◽  
Filippo Coletti ◽  
Jérémy Bulle ◽  
Timothée Vanderwielen ◽  
Tony Arts
Keyword(s):  
Numerical Method ◽  
Pressure Loss ◽  
Total Pressure ◽  
Cooling System ◽  
Differential Evolution Algorithm ◽  
Flow Region ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Cooling Channels

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In this first part of the paper, the design methodology of the cooling channel is presented. The minimization of the total pressure loss is achieved by means of a numerical optimization method that uses a metamodel-assisted differential evolution algorithm in combination with an incompressible Navier–Stokes solver. The profiles of the internal and external side of the bend are parameterized using piece-wise Bezier curves. This allows for a wide variety of shapes, respecting the manufacturability constraints of the design. The pressure loss is computed by the Navier–Stokes solver, which is based on a two-equation turbulence model and is available from the open source software OpenFOAM. The numerical method predicts an improvement of 36% in total pressure drop with respect to a circular U-bend, mainly due to the reduction of the separated flow region along the internal side of the bend. The resulting design is subjected to experimental validation, presented in Part II of the paper.

Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels: Part I—Numerical Method

2011 ◽  
Author(s):  
Tom Verstraete ◽  
Filippo Coletti ◽  
Je´re´my Bulle ◽  
Timothe´e Vanderwielen ◽  
Tony Arts
Keyword(s):  
Numerical Method ◽  
Pressure Loss ◽  
Total Pressure ◽  
Cooling System ◽  
Differential Evolution Algorithm ◽  
Flow Region ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Cooling Channels

This two-parts paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In this first part of the paper the design methodology of the cooling channel is presented. The minimization of the total pressure loss is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with an incompressible Navier-Stokes solver. The profiles of the internal and external side of the bend are parameterized using piece-wise Bezier curves. This allows for a wide variety of shapes, respecting the manufacturability constraints of the design. The pressure loss is computed by the Navier-Stokes solver, which is based on a two-equation turbulence model and is available from the open source software OpenFOAM. The numerical method predicts an improvement of 36% in total pressure drop with respect to a circular U-bend, mainly due to the reduction of the separated flow region along the internal side of the bend. The resulting design is subjected to experimental validation, presented in Part II of the paper.

Multi-Objective Optimization of a U-Bend for Minimal Pressure Loss and Maximal Heat Transfer Performance in Internal Cooling Channels

2013 ◽  
Author(s):  
Tom Verstraete ◽  
Jing Li
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Optimization Process ◽  
Internal Cooling ◽  
Multi Objective ◽  
Cooling Channels ◽  
Flow Motion

A multi-objective design optimization is performed on a U-bend in serpentine internal cooling channels. The aim is to achieve both minimized total pressure loss and maximized heat transfer ability. The optimization technique used is a two-level routine developed at the Von Karman Institute for Fluid Dynamics (VKI), featuring a Differential Evolution algorithm assisted by a metamodel, which is continuously updated during the course of the optimization process to increase its accuracy The geometries are carefully parameterized by means of Bezier curves. In total, 26 geometrical parameters are used as design variables, allowing an extensive variation of the U-bend geometries. The fluid dynamic and heat transfer performances of the selected geometries are predicted by a Reynolds-averaged Navier-Stokes solver in OpenFOAM. The result shows that dozens of optimized geometries of enhanced performances in both design objectives can be obtained after a few numbers of iterations. The enhancement ranges from roughly 12∼30% decrease in total pressure loss and a 8∼17% increase in heat flow rate. A clear trade-off between pressure loss and heat transfer is observed, allowing designers to select a compromising geometry between both criteria after the optimization process, depending on the application type of the internal cooling channel. Generally, a stronger secondary flow motion in the channel will be responsible for higher heat transfer at the cost of increased losses. A discussion is held on the geometrical features that have an impact on the secondary flow motion strength and lead to general applicable conclusions.

Adjoint Optimization of an Internal Cooling Channel U-Bend

2015 ◽  
Author(s):  
Sebastian Willeke ◽  
Tom Verstraete
Keyword(s):  
Steady State ◽  
Pressure Loss ◽  
Total Pressure ◽  
Design Space ◽  
Total Pressure Loss ◽  
Steepest Descent Method ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Gradient Based ◽  
Continuous Adjoint

This paper addresses the optimization of a two-dimensional U-bend passage of an internal serpentine cooling channel for reduced total pressure loss by means of a steepest-descent method. A steady-state incompressible flow is considered at a Reynolds number of 40,000 based on the bulk velocity at the domain inlet. The two-equation k-ε model is used for primal turbulence modeling. After only 30 design iterations, the gradient-based optimization results in a reduction of total pressure loss by 46% compared to the baseline geometry. To obtain the required objective gradients efficiently, a continuous adjoint approach is implemented in the OpenFOAM environment. Adjoint governing equations and boundary conditions are derived from state equations for steady-state, incompressible, turbulent flows under the assumption of frozen turbulence. Two different methods are proposed for modifying the shape of internal and external curves defining the duct geometry. The first method makes use of direct displacement of boundary grid points, allowing for a wide design space. The second, novel parameterization utilizes a projection of the surface sensitivities to an underlying Bézier curve. In this case, the Bézier control points are used as design variables. A comparison of both methods demonstrates a slightly lower performance improvement by the Bézier-based approach due to the reduced design freedom. This approach has, however, several practical advantages. Previous studies already addressed this optimization problem using gradient-free methods, but were limited in the degrees of freedom given to the shape variation. The present gradient-based optimization allows for a much larger design space and hence is used to compare the different methodologies. It shows that both optimizations result in similar shapes, although the gradient-based method allows for a slightly larger reduction in pressure loss due to the wider design space, while converging faster towards the optimum.

scholarly journals Constrained Shape Optimization of Airfoil Cascades Using a Navier-Stokes Solver and a Genetic/SQP Algorithm

1999 ◽  
Author(s):  
Brian H. Dennis ◽  
George S. Dulikravich ◽  
Zhen-Xue Han
Keyword(s):  
Flow Field ◽  
Shape Optimization ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Field Analysis ◽  
Navier Stokes ◽  
Conic Section ◽  
Aerodynamic Shape ◽  
Flow Field Analysis

The objective in this aerodynamic shape design effort is to minimize total pressure loss across the two-dimensional linear airfoil cascade row while satisfying a number of constraints. They included fixed axial chord, total torque, inlet and exit flow angles, and blade cross-section area, while maintaining thickness distribution greater than a minimum specified value. The aerodynamic shape optimization can be performed by using any available flow-field analysis code. For the analysis of the performance of intermediate cascade shapes we used an unstructured grid based compressible Navier-Stokes flow-field analysis code with k-e turbulence model. A robust genetic optimization algorithm was used for optimization and a constrained sequential quadratic programming was used enforcement of certain constraints. The airfoil geometry was parameterized using conic section parameters and B-splines thus keeping the number of geometric design variables to a minimum while achieving a high degree of geometric flexibility and robustness. Significant reductions of the total pressure loss were achieved using this constrained method for a supersonic exit flow axial turbine cascade.

scholarly journals The Influence of Downstream Passage on the Flow Within an Annular S-Shaped Duct

1997 ◽  
Author(s):  
Toyotaka Sonoda ◽  
Toshiyuki Arima ◽  
Mineyasu Oana
Keyword(s):  
High Pressure ◽  
Pressure Loss ◽  
Total Pressure ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Horseshoe Vortex ◽  
Meridional Flow ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Compressor Performance

Experimental and numerical investigations were carried out to gain a better understanding or the flow characteristics within an annular S-shaped duct, including the influence of the shape of the downstream passage located at the exit of the duct on the flow. A duct with six struts and the same geometry as that used to connect the compressor spools on our new experimental small two-spool turbofan engine was investigated. Two types of downstream passage were used. One type had a straight annular passage and the other a curved annular passage with a similar meridional flow path geometry to that of the centrifugal compressor. Results showed that the total pressure loss near the hub is large due to instability of the flow, as compared with that near the casing. Also, a vortex related to the horseshoe vortex was observed near the casing, in the case of the curved annular passage, the total pressure loss near the hub was greatly increased compared with the case of the straight annular passage, and the spatial position of the above vortex depends on the passage core pressure gradient. Furthermore, results of calculation using an in-house-developed three-dimensional Navier-Stokes code with a low Reynolds number k-ε turbulence model were in good qualitative agreement with experimental results. According to the simulation results, a region of very high pressure loss is observed near the hub at the duct exit with the increase of inlet boundary layer thickness. Such regions of high pressure loss may act on the downstream compressor as a large inlet distortion, and strongly affect downstream compressor performance.

The Influence of Downstream Passage on the Flow Within an Annular S-Shaped Duct

1998 ◽  
Vol 120 (4) ◽  
pp. 714-722 ◽  
Author(s):  
T. Sonoda ◽  
T. Arima ◽  
M. Oana
Keyword(s):  
High Pressure ◽  
Pressure Loss ◽  
Total Pressure ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Horseshoe Vortex ◽  
Meridional Flow ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Compressor Performance

Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the influence of the shape of the downstream passage located at the exit of the duct on the flow. A duct with six struts and the same geometry as that used to connect the compressor spools on our new experimental small two-spool turbofan engine was investigated. Two types of downstream passage were used. One type had a straight annular passage and the other a curved annular passage with a meridional flow path geometry similar to that of the centrifugal compressor. Results showed that the total pressure loss near the hub is large due to instability of the flow, as compared with that near the casing. Also, a vortex related to the horseshoe vortex was observed near the casing. In the case of the curved annular passage, the total pressure loss near the hub was greatly increased compared with the case of the straight annular passage, and the spatial position of this vortex depends on the passage core pressure gradient. Furthermore, results of calculation using an in-house-developed three-dimensional Navier–Stokes code with a low-Reynolds-number k–ε turbulence model were in good qualitative agreement with experimental results. According to the simulation results, a region of very high pressure loss is observed near the hub at the duct exit with the increase of inlet boundary layer thickness. Such regions of high pressure loss may act on the downstream compressor as a large inlet distortion, and strongly affect downstream compressor performance.

Loss Reduction in a 1.5 Stage Axial Turbine by Computer-Driven Stator Hub Contouring

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Hayder M. B. Obaida ◽  
Aldo Rona ◽  
J. Paul Gostelow
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Thermal Power ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Automatic Process ◽  
Loss Reduction ◽  
Component Level ◽  
Axial Turbine ◽  
Reynolds Averaged Navier Stokes

Improvements in stage isentropic efficiency and reductions in total pressure loss are sought in a 1.5 stage axial turbine. This is representative of power generation equipment used in thermal power cycles, which delivers about 80% of the 20 × 1012 kWh world-wide electricity. Component-level improvements are therefore timely and important toward achieving carbon dioxide global emission targets. Secondary flow loss reduction is sought by applying a nonaxisymmetric endwall design to the turbine stator hub. A guide groove directs the pressure side branch of the horseshoe vortex away from the airfoil suction side, using a parametric endwall hub surface, which is defined as to obtain first-order smooth boundary connections to the remainder of the passage geometry. This delays the onset of the passage vortex and reduces its associated loss. The Automatic Process and Optimization Workbench (apow) generates a Kriging surrogate model from a set of Reynolds-averaged Navier–Stokes simulations, which is used to optimize the hub surface. The three-dimensional steady Reynolds-averaged Navier–Stokes model with an axisymmetric hub is validated against reference experimental measurements from the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen. Comparative computational fluid dynamics (CFD) predictions with an optimized nonaxisymmetric hub show a decrease in the total pressure loss coefficient and an increase in the isentropic stage efficiency at and off design conditions.

Accurate Estimation of Profile Losses and Analysis of Loss Generation Mechanisms in a Turbine Cascade

2017 ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino ◽  
F. Bertini ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Pressure Loss ◽  
Total Pressure ◽  
Flow Region ◽  
Suction Side ◽  
Total Pressure Loss ◽  
Accurate Estimation ◽  
Turbine Cascade ◽  
Loss Mechanism ◽  
Generation Mechanisms

The paper analyzes losses and the loss generation mechanisms in a low-pressure turbine cascade by Proper-Orthogonal-Decomposition (POD) applied to measurements. Total pressure probes and time resolved particle image velocimetry (TR-PIV) are used to determine the flow field and performance of the blade with steady and unsteady inflow conditions varying the flow incidence. The total pressure loss co-efficient is computed by traversing two Kiel probes upstream and downstream of the cascade simultaneously. This procedure allows a very accurate estimation of the total pressure loss coefficient also in the potential flow region affected by incoming wake migration. The TR-PIV investigation concentrates on the aft portion of the suction side boundary layer downstream of peak suction. In this adverse pressure gradient region the interaction between the wake and the boundary layer is the strongest, and it leads to the largest deviation from a steady loss mechanism. POD applied to this portion of the domain provides a statistical representation of the flow oscillations by splitting the effects induced by the different dynamics. The paper also describes how POD can dissect the loss generation mechanisms by separating the contributions to the Reynolds stress tensor from the different modes. The steady condition loss generation, driven by boundary layer streaks and separation is augmented in presence of incoming wakes by the wake-boundary layer interaction and by the wake dilation mechanism. Wake migration losses have been found to be almost insensitive to incidence variation between nominal and negative (up to −9deg), while at positive incidence the losses have a steep increase due to the alteration of the wake path induced by the different loading distribution.

Effect of the honeycomb tip with injection on the aerodynamic performance in a 1.5-stage turbine

2020 ◽  
pp. 1-25
Author(s):  
Jianyang Yu ◽  
Yabo Wang ◽  
YanPing Song ◽  
Fu Chen
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Total Efficiency ◽  
Cavity Depth ◽  
Tip Leakage

Abstract Three kinds of rotor tip configurations have been investigated numerically in the LISA 1.5-stage turbine, including the flat tip, the honeycomb tip and the honeycomb tip with injection. The effect of the cavity depth and the injection mass flow rate on the turbine performance is studied in detail, evaluated by the isentropic total-to-total efficiency and the tip leakage mass flow rate. The Reynolds-averaged Navier-Stokes (RANS) method and the k-ω turbulence model are adopted in all the present computations. The numerical results show that the first stage efficiency is increased by up to 0.66% and the tip leakage mass flow rate is reduced by about 1.87% of the main flow. The pressure field and the flow feature inside the gap are explored. The flow structures and the total pressure loss contours in the rotor passage are presented. Finally, the total pressure loss is newly defined by considering the injection effect. It is indicated that the injection mass flow rate should be carefully determined for excellent overall performance.

Aerodynamics of a Covered Trailing Edge Vane: Effects of Blowing Rate, Reynolds Number, and External Turbulence

2009 ◽  
Author(s):  
I. Jaswal ◽  
E. Erickson ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Total Pressure ◽  
Large Scale ◽  
Total Pressure Loss ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Number Range ◽  
Exit Survey

A covered trailing edge vane was developed by opening a fully loaded incompressible vane to accept an internal flow passage. The internal passage was filled with a high solidity internal cooling scheme. Exit survey measurements were acquired downstream from a large scale low speed linear cascade test section using a 5-hole cone probe at 1/4 axial chord downstream from the vane trailing edge. Exit survey measurements detailed total pressure loss, turning angle and secondary velocities. Exit survey measurements were conducted across a range of blowing rates (25% to 150% design), Reynolds numbers (500,000, 1,000,000 and 2,000,000) and turbulence levels [low (0.7%), grid (8.5%) and aero-combustor (13.5%)]. Losses for a thickened baseline vane (no blowing, same profile) were also acquired across the Reynolds number range and turbulence conditions. Vane midspan pressure and heat transfer distributions were acquired to help document the state of the boundary layers developing on the vane surface. Measurements are presented in terms of total pressure loss contours with secondary velocities and spanwise distributions of circumferentially averaged losses and turning angles. Overall loss values have been compared with measurements taken using the original base vane and a conventional gill slot vane. Comparisons between the base vane and the covered base vane show an incremental increase in total pressure losses of about 0.95% due the thicker trailing edge. Comparisons between the gill slot (pressure side cutback) and the covered trailing edge vane at comparable flow conditions show a much smaller loss penalty. Loss data for the gill slot vane suggest that both separation off the gill slot lip and the discharge of low momentum fluid are responsible for significant incremental losses above the base vane. The covered trailing edge vane has no additional surface with separation losses which penalizes the aerodynamics. Heat transfer rates for the internal cooling scheme are documented in a separate paper [1].

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