Study of Relative Endwall Motion Effects in a Compressor Cascade Through Direct Numerical Simulations

Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, such as the relative motion between blade and endwall. In this study, three different relative endwall velocities are analyzed. The effect of the relative motion between endwall and blade in a linear compressor cascade is studied through direct numerical simulations. Results show a significant change in the secondary flow structure within the passage. Most notably, the tip leakage vortex is displaced away from the blade. Still, the blade spanwise range affected by the secondary flow field is similar to the case without relative endwall motion. At the outlet plane, a stratification of the total pressure losses and the exit flow angle is found, which overshadows any blade wake effects near the endwall.

Study of Relative Endwall Motion Effects in a Compressor Cascade Through Direct Numerical Simulations

Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, among them the relative motion between blade and endwall. In this study three different relative endwall velocities are analysed. The effect of the relative motion between endwall and blade in a linear compressor cascade is studied through Direct Numerical Simulations. Results show a significant change in the secondary flow structure within the passage. Most notably, the tip leakage vortex is displaced away from the blade. Still, the blade spanwise range affected by the secondary flow field is similar to the case without relative endwall motion. At the outlet plane, a stratification of the total pressure losses and the exit flow angle is found, which overshadows any blade wake effects near the endwall.

Experimental and Numerical Investigation of the Loss Coefficient of a 90° Pipe Bend for Power-Law Fluid

This study presents an investigation on the flow of two non-Newtonian fluids. These materials can be found in industrial environment, such as pharmaceutical and food industries, and also in wastewater treatment. In industrial environment, these fluids are usually driven by pumps between two workstations in the system, which represents a significant proportion of the costs. In order to operate the system cost-efficiency and environment friendly accurate sizing is necessary, which requires data on the hydraulic resistance of the elements. In the case of Newtonian fluids, these parameters are well-known. However, the non-Newtonian fluids have a considerably narrower literature, so laboratory and numerical tests are desirable. In our work, the hydraulic losses of two real non-Newtonian fluids were studied which can be described with the power law rheological model. These studies included laboratory measurements and numerical simulations (Computational Fluid Dynamics, CFD), respectively. We investigated the friction factor of a straight pipe and loss coefficient of an elbow (R/D=2). The calculations were validated with our laboratory measurements and compared with the literature. Furthermore, the flow pattern in the pipe bend was also examined. The study presents the applicability and importance of the modification of the Reynolds number. Furthermore, the velocity profiles and the secondary flow structure in the elbow are also presented.

Developing Secondary Flow and Heat Transfer in the Entrance Region of a Square Channel With 45° Crossed Rib Arrangement

This paper presents developing secondary flow and heat transfer measurements in a ribbed cooling channel. Experiments are carried out for Reynolds number ranging from 25,000–140,000. Regionally averaged local heat transfer measurements are conducted using heated copper segments. Flow measurements are carried out using a miniature five-hole pressure probe and presented for cross sections at intervals of 1.8 hydraulic diameters dh in flow direction. Results are compared to numerical simulations using explicit algebraic Reynolds stress and turbulent heat transfer models. The paper focuses on the entrance region where secondary flow structure has not emerged yet. The findings show that the well-known secondary flow structure of the crossed rib configuration, consisting of one large single rotating secondary flow, is not established until approximately 6–7 dh in main flow direction. Instead two opposed vortices are identified which dominate the flow characteristics and provide an increase in heat transfer of up to 15–20% when compared to the periodically developed flow condition. Thus, for the first time to the author’s knowledge, the paper describes in detail the developing secondary flow in a crossed rib arrangement and links it to the heat transfer distribution observed. In summary, this paper stresses the importance of the developing flow region for the design process in convection cooled gas turbines, especially for short channels of high pressure blades and vanes, as it has a significant effect on cooling channel heat transfer performance.

Effect of Axial Velocity Density Ratio on the Performance of a Controlled Diffusion Airfoil Compressor Cascade

Axial Velocity Density Ratio (AVDR) is an important parameter to check the two-dimensionality of cascade flows. It can have significant influence on the cascade performance and the secondary flow structure. In the present study, the effect of AVDR has been investigated on a highly loaded Controlled Diffusion airfoil compressor cascade. Detailed 3D Computational Fluid Dynamics (CFD) studies were carried out with the cascade at five different AVDRs. Key aerodynamic performance parameters and flow structure through the cascade were analyzed in detail. CFD results of one AVDR were validated with the experimental cascade test data and were seen to be in good agreement. Loss characteristics of the cascade varied significantly with change in AVDR. Increase in AVDR postponed the point of separation on the suction surface, produced thinner boundary layers and caused substantial drop in the pressure loss coefficient. Strong end wall vortices were noticed at AVDR of 1.177. At higher AVDRs, the flow was well guided even close to the end wall and the secondary flows diminished. The loading initially improved with increase in AVDR. Beyond a certain limit, further increase in AVDR offered no improvements to the loading but rather resulted in drop in diffusion and deviation.

Nekomimi Film Cooling Holes Configuration Under Conjugate Heat Transfer Conditions

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result in increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. Today it is common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also called kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRVs. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The NEKOMIMI configuration and two conventional cooling hole configurations (cylindrical and shaped holes) has been investigated numerically under adiabatic and conjugate heat transfer conditions. The influence of the conjugate heat transfer on the secondary flow structure has been analysed. In conjugate heat transfer calculations, it cannot directly derived from the surface temperature distribution if the reached cooling effectiveness values are due to the improved hole configuration with improved secondary flow structure or due to the heat conduction in the material. Therefore, a methodology has been developed, to distinguish between cooling effectiveness due to heat conduction in the material and film cooling flow over the surface. The numerical results shows that for the NEKOMIMI configuration, 77% of the reached overall cooling effectiveness is due to film cooling with improved flow structure in the secondary flow (ACRV) and 23% due to heat conduction in the material. For the cylindrical hole configuration, 10% of the reached overall cooling effectiveness is due to the film cooling flow structure and 90% due to heat conduction in the material.

The Effect of Endwall Manufacturing Variations on Turbine Performance

Turbine blades and vanes of modern aero-engines are commonly manufactured by casting. The casting process often introduces slight geometry variations. In the endwall region this leads to inter-platform steps, gaps and leakage flows. This paper determines the underlying loss mechanisms associated with each of these geometric features and guides designers in minimizing their impact on efficiency. The paper shows that the presence of an inter-platform step causes a pair of vortical structures to be superimposed onto the blade existing secondary flow structure. These are shown to always increase loss. When manufacture variations are considered the optimal design intent blade is shown to be one where the suction side endwall is lower than the pressure side endwall. The paper shows that when leakage mass flow is introduced the presence of a step can either raise or reduce loss. A correlation which gives the optimal step height for a set leakage mass flow is presented. In the final part of the paper measured engine vane geometries are used to determine the impact of endwall geometry variation on turbine stage efficiency.