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Papers by Zuheyr Alsalihi

Lecture Notes in Engineering, 1989

Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically mode... more Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically model unsteady laminar or turbulent, compressible or incompressible flow at low Reynolds numbers over a Wortmann FX63-137 airfoil. The hyperbolic grid generation ...

A Conjugate Heat Transfer (CHT) analysis allows the calculation of the heat transfer and temperat... more A Conjugate Heat Transfer (CHT) analysis allows the calculation of the heat transfer and temperature of a body placed in a fluid. The CHT analysis takes into account both the conduction in the solid and the convection in the fluid. Present paper describes a CHT method that uses two separate solvers: one CFD solver dedicated to the flow calculation and one Finite Element Analysis (FEA) solver for the computation of the heat transfer in the solid. Several methods, combining both codes in order to solve the CHT problem, are explained andevaluated. The CHT method is tested on two turbomachine applications.

Volume 1A: Aircraft Engine; Fans and Blowers, 2014

In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the ef... more In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the effective devices to improve the pressure recovery at design flow rate while guaranteeing a wide operating range. The improvement is mainly attributed to the so called secondary flow effect, which reduces the flow separation on the LSD blade at small flow rates. However, it is very difficult to find out the effective shape of the blade in order to promote this secondary flow effect. In this paper, a multipoint and multi-objective optimization technique is applied to design the LSD blade of a centrifugal blower. The optimization method has been developed at the von Karman Institute for Fluid Dynamics (VKI), which makes use of an evolutionary algorithm, a metamodel as a rapid exploration tool, and a high fidelity 3D Navier-Stokes solver.The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Seven detailed design parameters describing the shape and position of the LSD vane were introduced, e.g. the radial spacing between impeller exit and the LSD leading edge, the radial chord length and the mean camber angle distribution of the LSD blade with five control points. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect. This is fully corresponding to the CFD predictions and demonstrates the effectiveness of the optimization methodology, by limiting the experimental testing to only two geometries.Copyright © 2014 by ASME

Hypersonic Flows for Reentry Problems, 1991

Steady, laminar hypersonic viscous flows over semi-infinite flat plates and two-dimensional compr... more Steady, laminar hypersonic viscous flows over semi-infinite flat plates and two-dimensional compression ramps are calculated. Surface pressure, skin friction and heat transfer distributions as well as flow structure plots (isoline contours) are presented for Mach numbers of 5, 10 and 14.1 and for unit Reynolds numbers of 3 to 6 million per meter.

A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or... more A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or laminar, (thin-layer) Navier-Stokes equations for transonic flow fields about airfoils. The technique employed is hyperbolic grid generation with the condition of orthogonality and cell area ( ...

Volume 1A: Aircraft Engine; Fans and Blowers, 2014

In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the ef... more In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the effective devices to improve the pressure recovery at design flow rate while guaranteeing a wide operating range. The improvement is mainly attributed to the so called secondary flow effect, which reduces the flow separation on the LSD blade at small flow rates. However, it is very difficult to find out the effective shape of the blade in order to promote this secondary flow effect. In this paper, a multipoint and multi-objective optimization technique is applied to design the LSD blade of a centrifugal blower. The optimization method has been developed at the von Karman Institute for Fluid Dynamics (VKI), which makes use of an evolutionary algorithm, a metamodel as a rapid exploration tool, and a high fidelity 3D Navier-Stokes solver.The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Seven detailed design parameters describing the shape and position of the LSD vane were introduced, e.g. the radial spacing between impeller exit and the LSD leading edge, the radial chord length and the mean camber angle distribution of the LSD blade with five control points. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect. This is fully corresponding to the CFD predictions and demonstrates the effectiveness of the optimization methodology, by limiting the experimental testing to only two geometries.Copyright © 2014 by ASME

Journal of Turbomachinery, 2012

This paper presents a multidisciplinary design optimization of a turbocharger radial turbine for ... more This paper presents a multidisciplinary design optimization of a turbocharger radial turbine for automotive applications with the aim to improve two major manufacturer requirements: the total-to-static efficiency and the moment of inertia of the radial turbine impeller. The search for the best design is constrained by mechanical stress limitations, by the mass flow and power, and by aerodynamic constraints related to the isentropic Mach number distribution on the rotor blade. The optimization of the radial turbine is performed with a two-level optimization algorithm developed at the von Karman Institute for Fluid Dynamics. The system makes use of a differential evolution algorithm, an artificial neural network (ANN), and a database as a compromise between accuracy and computational cost. The ANN performance predictions are periodically validated by means of accurate steady state 3D Navier-Stokes and centrifugal stress computations. The results show that it is possible to improve the...

... of steady-state regime. Two radial-flux machines are currently under investigation: a permane... more ... of steady-state regime. Two radial-flux machines are currently under investigation: a permanent magnet synchronous machine (PMSM) and a switched reluctancemachine (SRM 6/4 configuration). In contrast to normal designs ...

Low Reynolds number aerodynamics, 1989

Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically mode... more Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically model unsteady laminar or turbulent, compressible or incompressible flow at low Reynolds numbers over a Wortmann FX63-137 airfoil. The hyperbolic grid generation ...

NASA STI/Recon Technical Report N, 1987

A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or... more A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or laminar, (thin-layer) Navier-Stokes equations for transonic flow fields about airfoils. The technique employed is hyperbolic grid generation with the condition of orthogonality and cell area ( ...

Journal of Turbomachinery, 2013

This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means... more This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means of a multiobjective optimization system. The latter makes use of a differential evolutionary algorithm in combination with an Artificial Neural Network and a 3D Navier-Stokes solver. Operating it on a cluster of 30 processors enabled the evaluation of the off-design performance and the exploration of a large design space composed of the camber line and spanwise distribution of sweep and chord length. Objectives were an increase of efficiency at unchanged stall margin by controlling the shock waves and off-design performance curve. First designs of single blade rows allowed a better understanding of the impact of the different design parameters. Forward sweep with unchanged camber improved the peak efficiency by only 0.3% with the same stall margin. Backward sweep with an optimized S shaped camber line improved the efficiency by 0.6% at unchanged stall margin. It is explained how the cam...

Lecture Notes in Engineering, 1989

Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically mode... more Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically model unsteady laminar or turbulent, compressible or incompressible flow at low Reynolds numbers over a Wortmann FX63-137 airfoil. The hyperbolic grid generation ...

A Conjugate Heat Transfer (CHT) analysis allows the calculation of the heat transfer and temperat... more A Conjugate Heat Transfer (CHT) analysis allows the calculation of the heat transfer and temperature of a body placed in a fluid. The CHT analysis takes into account both the conduction in the solid and the convection in the fluid. Present paper describes a CHT method that uses two separate solvers: one CFD solver dedicated to the flow calculation and one Finite Element Analysis (FEA) solver for the computation of the heat transfer in the solid. Several methods, combining both codes in order to solve the CHT problem, are explained andevaluated. The CHT method is tested on two turbomachine applications.

Volume 1A: Aircraft Engine; Fans and Blowers, 2014

In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the ef... more In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the effective devices to improve the pressure recovery at design flow rate while guaranteeing a wide operating range. The improvement is mainly attributed to the so called secondary flow effect, which reduces the flow separation on the LSD blade at small flow rates. However, it is very difficult to find out the effective shape of the blade in order to promote this secondary flow effect. In this paper, a multipoint and multi-objective optimization technique is applied to design the LSD blade of a centrifugal blower. The optimization method has been developed at the von Karman Institute for Fluid Dynamics (VKI), which makes use of an evolutionary algorithm, a metamodel as a rapid exploration tool, and a high fidelity 3D Navier-Stokes solver.The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Seven detailed design parameters describing the shape and position of the LSD vane were introduced, e.g. the radial spacing between impeller exit and the LSD leading edge, the radial chord length and the mean camber angle distribution of the LSD blade with five control points. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect. This is fully corresponding to the CFD predictions and demonstrates the effectiveness of the optimization methodology, by limiting the experimental testing to only two geometries.Copyright © 2014 by ASME

Hypersonic Flows for Reentry Problems, 1991

Steady, laminar hypersonic viscous flows over semi-infinite flat plates and two-dimensional compr... more Steady, laminar hypersonic viscous flows over semi-infinite flat plates and two-dimensional compression ramps are calculated. Surface pressure, skin friction and heat transfer distributions as well as flow structure plots (isoline contours) are presented for Mach numbers of 5, 10 and 14.1 and for unit Reynolds numbers of 3 to 6 million per meter.

A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or... more A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or laminar, (thin-layer) Navier-Stokes equations for transonic flow fields about airfoils. The technique employed is hyperbolic grid generation with the condition of orthogonality and cell area ( ...

Volume 1A: Aircraft Engine; Fans and Blowers, 2014

In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the ef... more In radial compressors or blowers, a low solidity circular cascade diffuser (LSD) is one of the effective devices to improve the pressure recovery at design flow rate while guaranteeing a wide operating range. The improvement is mainly attributed to the so called secondary flow effect, which reduces the flow separation on the LSD blade at small flow rates. However, it is very difficult to find out the effective shape of the blade in order to promote this secondary flow effect. In this paper, a multipoint and multi-objective optimization technique is applied to design the LSD blade of a centrifugal blower. The optimization method has been developed at the von Karman Institute for Fluid Dynamics (VKI), which makes use of an evolutionary algorithm, a metamodel as a rapid exploration tool, and a high fidelity 3D Navier-Stokes solver.The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Seven detailed design parameters describing the shape and position of the LSD vane were introduced, e.g. the radial spacing between impeller exit and the LSD leading edge, the radial chord length and the mean camber angle distribution of the LSD blade with five control points. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect. This is fully corresponding to the CFD predictions and demonstrates the effectiveness of the optimization methodology, by limiting the experimental testing to only two geometries.Copyright © 2014 by ASME

Journal of Turbomachinery, 2012

This paper presents a multidisciplinary design optimization of a turbocharger radial turbine for ... more This paper presents a multidisciplinary design optimization of a turbocharger radial turbine for automotive applications with the aim to improve two major manufacturer requirements: the total-to-static efficiency and the moment of inertia of the radial turbine impeller. The search for the best design is constrained by mechanical stress limitations, by the mass flow and power, and by aerodynamic constraints related to the isentropic Mach number distribution on the rotor blade. The optimization of the radial turbine is performed with a two-level optimization algorithm developed at the von Karman Institute for Fluid Dynamics. The system makes use of a differential evolution algorithm, an artificial neural network (ANN), and a database as a compromise between accuracy and computational cost. The ANN performance predictions are periodically validated by means of accurate steady state 3D Navier-Stokes and centrifugal stress computations. The results show that it is possible to improve the...

... of steady-state regime. Two radial-flux machines are currently under investigation: a permane... more ... of steady-state regime. Two radial-flux machines are currently under investigation: a permanent magnet synchronous machine (PMSM) and a switched reluctancemachine (SRM 6/4 configuration). In contrast to normal designs ...

Low Reynolds number aerodynamics, 1989

Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically mode... more Time-averaged two-dimensional compressible Navier-Stokes equations are solved to numerically model unsteady laminar or turbulent, compressible or incompressible flow at low Reynolds numbers over a Wortmann FX63-137 airfoil. The hyperbolic grid generation ...

NASA STI/Recon Technical Report N, 1987

A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or... more A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or laminar, (thin-layer) Navier-Stokes equations for transonic flow fields about airfoils. The technique employed is hyperbolic grid generation with the condition of orthogonality and cell area ( ...

Journal of Turbomachinery, 2013

This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means... more This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means of a multiobjective optimization system. The latter makes use of a differential evolutionary algorithm in combination with an Artificial Neural Network and a 3D Navier-Stokes solver. Operating it on a cluster of 30 processors enabled the evaluation of the off-design performance and the exploration of a large design space composed of the camber line and spanwise distribution of sweep and chord length. Objectives were an increase of efficiency at unchanged stall margin by controlling the shock waves and off-design performance curve. First designs of single blade rows allowed a better understanding of the impact of the different design parameters. Forward sweep with unchanged camber improved the peak efficiency by only 0.3% with the same stall margin. Backward sweep with an optimized S shaped camber line improved the efficiency by 0.6% at unchanged stall margin. It is explained how the cam...