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Papers by hakim kadhim

Research paper thumbnail of 2D Numerical Study of Heat Transfer Enhancement Using Fish-Tail Locomotion Vortex Generators

Mathematical Modelling of Engineering Problems, 2021

In this paper, a numerical simulation is performed to study the effect of two types of concave vo... more In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

Research paper thumbnail of Design optimization workflow and performance analysis for contoured endwalls of axial turbines

Energy

Advances in computer-based optimization techniques can be used to enhance the efficiency of energ... more Advances in computer-based optimization techniques can be used to enhance the efficiency of energy conversions processes, such as by reducing the aerodynamic loss in thermal power plant turbomachines. One viable approach for reducing this flow energy loss is by endwall contouring. This paper implements a design optimization workflow for the casing geometry of a 1.5 stage axial turbine, towards mitigating secondary flows. Two different parametric casing surface definitions are used in the optimization process. The first method is a new nonaxisymmetric casing design using a novel surface definition. The second method is an established diffusion design technique. The designs are tested on a threedimensional axial turbine RANS model. Computer-based optimization of the surface topology is demonstrated towards automating the design process. This is implemented using Automated Process and Optimization Workbench (APOW) software. Kriging is used to accelerate the optimization process. The optimization and its sensitivity analysis give confidence that a good predictive ability is obtained by the Kriging surrogate model used in the prototype design process tested in this work. A flow analysis confirms the positive impact of the optimized casing groove design on the stage isentropic efficiency compared to the diffusion design and compared to the benchmark axisymmetric design.

Research paper thumbnail of Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

International Journal of Mechanical Sciences

The interaction of secondary flows with the main passage flow in turbomachines results in entropy... more The interaction of secondary flows with the main passage flow in turbomachines results in entropy generation and in aerodynamic loss. This loss source is most relevant to low aspect ratio blades. One approach for reducing this flow energy loss is by end-wall contouring. However, limited work has been reported on using non-axisymmetric end-walls at the stator casing and on its interaction with the tip leakage flow. In this paper, a non-axisymmetric end-wall design method for the stator casing is implemented through a novel surface definition, towards mitigating secondary flow losses. This design is tested on a three-dimensional axial turbine RANS model built in OpenFOAM Extend 3.2, with − SST turbulence closure. Flow analysis confirm the foundations of the new surface definition approach, which is implemented using Alstom Process and Optimization Workbench (APOW) software. Computer-based optimization of the surface topology is demonstrated towards automating the design process of axial turbines in an industrial design workflow. The design is optimized using the total pressure loss across the first stator and across the full stage, as the target function. Numerical predictions of the 1.5 stage axial turbine show the positive impact of the optimized casing design on the efficiency that increases by 0.69% against the benchmark axisymmetric stage from RTWH Aachen, which is validated against experiment. The new non-axisymmetric casing is also beneficial at off-design condition. The effective mitigation of the secondary flows is predicted to give a 0.73% efficiency gain off-design.

Research paper thumbnail of Perspectives on the Treatment of Secondary Flows in Axial Turbines

Energy Procedia

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Research paper thumbnail of 2D Numerical Study of Heat Transfer Enhancement Using Fish-Tail Locomotion Vortex Generators

Mathematical Modelling of Engineering Problems, 2021

In this paper, a numerical simulation is performed to study the effect of two types of concave vo... more In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

Research paper thumbnail of Design optimization workflow and performance analysis for contoured endwalls of axial turbines

Energy

Advances in computer-based optimization techniques can be used to enhance the efficiency of energ... more Advances in computer-based optimization techniques can be used to enhance the efficiency of energy conversions processes, such as by reducing the aerodynamic loss in thermal power plant turbomachines. One viable approach for reducing this flow energy loss is by endwall contouring. This paper implements a design optimization workflow for the casing geometry of a 1.5 stage axial turbine, towards mitigating secondary flows. Two different parametric casing surface definitions are used in the optimization process. The first method is a new nonaxisymmetric casing design using a novel surface definition. The second method is an established diffusion design technique. The designs are tested on a threedimensional axial turbine RANS model. Computer-based optimization of the surface topology is demonstrated towards automating the design process. This is implemented using Automated Process and Optimization Workbench (APOW) software. Kriging is used to accelerate the optimization process. The optimization and its sensitivity analysis give confidence that a good predictive ability is obtained by the Kriging surrogate model used in the prototype design process tested in this work. A flow analysis confirms the positive impact of the optimized casing groove design on the stage isentropic efficiency compared to the diffusion design and compared to the benchmark axisymmetric design.

Research paper thumbnail of Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

International Journal of Mechanical Sciences

The interaction of secondary flows with the main passage flow in turbomachines results in entropy... more The interaction of secondary flows with the main passage flow in turbomachines results in entropy generation and in aerodynamic loss. This loss source is most relevant to low aspect ratio blades. One approach for reducing this flow energy loss is by end-wall contouring. However, limited work has been reported on using non-axisymmetric end-walls at the stator casing and on its interaction with the tip leakage flow. In this paper, a non-axisymmetric end-wall design method for the stator casing is implemented through a novel surface definition, towards mitigating secondary flow losses. This design is tested on a three-dimensional axial turbine RANS model built in OpenFOAM Extend 3.2, with − SST turbulence closure. Flow analysis confirm the foundations of the new surface definition approach, which is implemented using Alstom Process and Optimization Workbench (APOW) software. Computer-based optimization of the surface topology is demonstrated towards automating the design process of axial turbines in an industrial design workflow. The design is optimized using the total pressure loss across the first stator and across the full stage, as the target function. Numerical predictions of the 1.5 stage axial turbine show the positive impact of the optimized casing design on the efficiency that increases by 0.69% against the benchmark axisymmetric stage from RTWH Aachen, which is validated against experiment. The new non-axisymmetric casing is also beneficial at off-design condition. The effective mitigation of the secondary flows is predicted to give a 0.73% efficiency gain off-design.

Research paper thumbnail of Perspectives on the Treatment of Secondary Flows in Axial Turbines

Energy Procedia

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.