Streamwise Angle Research Articles

The cooling performance of three-row compound angle holes on the suction surface of a rotating turbine blade

Experiments were carried out to study the effects of compound angle, hole arrangement, and blowing ratio on the film cooling performance of multiple rows of holes on the suction surface of a turbine blade. The turbine worked at rotational speed of 600 rpm corresponding to the rotational Reynolds number of 5.36 × 105. Three rows of cylindrical holes arranged in line or in stagger were drilled on the rotor blade suction surface at the streamwise location of 12.4%, 17.8%, and 23.2%, respectively. Three compound angles, with the same streamwise angle of 45° but different lateral deflection angles of 45°, 0°, and −45°, were studied. The film cooling effectiveness was obtained using pressure sensitive paint (PSP) technique with average blowing ratios varied from 0.5 to 2.0. The results showed that the application of compound angle changes the jet direction in the near-hole region and makes the film spread laterally. Compared with the film cooling without compound angle, using positive and negative compound angle can improve overall average film cooling effectiveness by about 20% and 25%, respectively. The effects of the secondary flow also can be weakened. A stagger film trajectory arrangement can achieve more uniform film coverage with higher overall film cooling effectiveness. The film trajectory arrangement of a positive compound angle injection is determined by the combined effect of hole arrangement and blowing ratio. While, the film trajectory arrangement of a negative compound angle injection is almost the same as the hole arrangement and nearly does not change with the blowing ratio.

The cooling performance of multiple rows of film holes on the suction surface of a turbine blade under rotating conditions

In this paper, the experimental results on the cooling performance of multiple rows of holes on the suction surface of a turbine blade were indicated. The effects of hole arrangement, blowing ratio, and rotation on the film cooling performance were analyzed. Four different film hole arrangements were studied. Each blade was modeled with three rows of cylindrical holes with streamwise angle of 45°. The first and the second injection rows were fixed at the position of 12.4% and 17.8% of the streamwise length of the suction surface, respectively. The third injection row was located at streamwise location of either 23.2% or 34%. To investigate the rotation effect, experiments were performed at three rotational speeds of 400 rpm, 600 rpm, and 800 rpm corresponding to the rotational Reynolds number of 3.57 × 105, 5.36 × 105, and 7.15 × 105, respectively. Average blowing ratios of 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0 were tested. Adiabatic film cooling effectiveness was obtained using pressure sensitive paint (PSP) technique. The results showed that inward deflection for the trajectories complicates the superposition principle. Staggered rows of holes can achieve more uniform film coverage and higher film cooling effectiveness. For the case with small array spacing between each adjacent rows, the film cooling area is too concentrated and can achieve better film cooling performance only at a small blowing ratio. The increasing rotational speed slightly weakens the tendency of inward film deflection and increases the film cooling effectiveness at a low blowing ratio.

Experimental study of film cooling over a fiber-reinforced composite plate with anisotropic thermal conductivity

An experimental investigation was carried out to analyze the film cooling performance over a fiber-reinforced composite plate with anisotropic thermal conductivity (ATC). The influence of the ATC and its spatial variations on the cooling effect under different blowing ratios was studied. It was found that the heat transfer in the plate was enhanced in the direction with higher thermal conductivity. The average value and the uniformity of the cooling efficiency changed with different inclined angles between the directions of the ATC and the mainstream. The highest average cooling efficiency was achieved with different values of the stream-wise angle α and the span-wise angle β when different regions downstream of the film cooling were considered. For example, when the blowing ratio was equal to 0.5, the corresponding α and β for the highest average cooling efficiency in the downstream region (1D ≤ X ≤ 5D) were 60° and 0°, respectively. For the downstream region (0D ≤ X ≤ 10D), the corresponding α and β were 35° and 60°, respectively. When the blowing ratio was different, the affected laws of α and β also exhibited variations.

Numerical Approach at Flat Plate for Predicting the Film Cooling Effectiveness Part A: Effect Blowing Ratio

Film cooling is vital for gas turbine blades to protect them from thermal stresses and high temperatures due to the hot gas flow in the blade surface. Film cooling is applied to almost all external surfaces associated with aerodynamic profiles that are exposed to hot combustion gases such as main bodies, end-walls, blade tips and leading edges. In a review of the literature, it was found that there are strong effects of free-stream turbulence, surface curvature and hole shape on film cooling performance also blowing ratio. The performance of the film cooling is difficult to predict due to the inherent complex flow fields along the surfaces of the airfoil components in the turbine engines. From all what we introducing the film cooling is reviewed through a discussion of the analyses methodologies, a physical description, and the various influences on film-cooling performance. Initially Computational analysis was done on a flat plate with hole inclined at 55° to the surface plate. This study focuses on the efficient computation of film cooling flows with three blowing ratio. The numerical results show the effectiveness cooling and heat transfer behavior with increasing injection blowing ratio M (0.5, 1, and 1.5). The influence of increased blade film cooling can be assessed via the values of Nusselt number in terms of reduced heat transfer to the blade. Predictions of film effectiveness are compared with experimental results for a circular jet at blowing ratios ranging from 0.5, 1.0 and 1.5. The present results are obtained at a free stream turbulence of 10%, which are the typical conditions upstream of the effectiveness is generally lower for a large stream-wise angle of 55°.

Improvement of film cooling effectiveness with a small downstream block body

The aim of this study is to predict the improvement in film cooling performance over a flat plate through a single row of cylindrical holes with different streamwise angles by using the Ansys CFX software package. In order to improve the film cooling effectiveness, a short crescent-shaped block is placed downstream of a cylindrical cooling hole. The numerical results of the cylindrical hole without the downstream short crescent-shaped block are compared with experimental data.

Numerical Computation and Optimization of Turbine Blade Film Cooling

The effect of film cooling parameters on the cooling effectiveness of an actual turbine blade is studied numerically. Film cooling parameters such as the hole shape, holes distribution, blowing ratio, streamwise angle, and spanwise angle are investigated to select the appropriate cooling parameters. Unstructured finite volume technique is used to solve the steady, three-dimensional, and compressible Navier-Stokes equations. Using one cooling holes array indicates that the average overall film cooling effectiveness is enhanced by decreasing the streamwise angle for high blowing ratio on the suction side of the turbine blade. The film cooling effectiveness is enhanced on the pressure side for a blowing ratio of unity. In addition, the cooling effectiveness increases by increasing the lateral and forward diffusion angles.The computations reveal that the efficiency of cooling is decreased at the leading edge due to the large surface curvature of the blade. The presence of compound shape (spanwise angle) enhanced the film cooling effectiveness on the two sides. Multistagger cooling hole arrays are investigated and the results indicate that five-stagger cooling arrays on the pressure side and three-stagger cooling arrays on the suction side with LFDCA-9.3-14.6 hole shape are enough to have good cooling of the two sides using 2.17% bleed air of the engine.

An Experimental Investigation of Showerhead Film Cooling Performance on a Turbine Blade

Experimental tests were performed to investigate the film cooling performance at the leading edge region of a turbine blade using the Infrared Radiation (IR) thermography technique. The test blades were enlarged by five times the natural size with three showerhead rows of radial-angle hole and one row of streamwise angle hole on pressure and suction side, respectively. Six different leading edge cooling geometries were designed by varying the radial angle from 35°to 90°. The effects of mainstream Reynolds number and coolant-to-mainstream blowing ratio were discussed. Results show that the blowing ratio has a marked influence on the cooling effectiveness with the existence of an optimum blowing ratio. High mainstream Reynolds number produces larger coolant flow rate and hence better cooling effectiveness. For x/C<0.15 on suction side close to the stagnation region and the overall pressure side, small radial angle improves the leading edge film cooling performance,whereas large radial angle facilitates the effectiveness downstream of x/C>0.15 on suction side. In current investigation, 45° showerhead radial angle relatively produces the least pressure loss and 75° or 90° gives the most aerodynamic loss that increases with the blowing ratio.

Film Cooling Optimization Using Numerical Computation of the Compressible Viscous Flow Equations and Simplex Algorithm

Film cooling is vital to gas turbine blades to protect them from high temperatures and hence high thermal stresses. In the current work, optimization of film cooling parameters on a flat plate is investigated numerically. The effect of film cooling parameters such as inlet velocity direction, lateral and forward diffusion angles, blowing ratio, and streamwise angle on the cooling effectiveness is studied, and optimum cooling parameters are selected. The numerical simulation of the coolant flow through flat plate hole system is carried out using the “CFDRC package” coupled with the optimization algorithm “simplex” to maximize overall film cooling effectiveness. Unstructured finite volume technique is used to solve the steady, three-dimensional and compressible Navier-Stokes equations. The results are compared with the published numerical and experimental data of a cylindrically round-simple hole, and the results show good agreement. In addition, the results indicate that the average overall film cooling effectiveness is enhanced by decreasing the streamwise angle for high blowing ratio and by increasing the lateral and forward diffusion angles. Optimum geometry of the cooling hole on a flat plate is determined. In addition, numerical simulations of film cooling on actual turbine blade are performed using the flat plate optimal hole geometry.

The effect of a small isolated roughness element on the forces on a sphere in uniform flow

The effect of an isolated roughness element on the forces on a sphere was examined for a Reynolds number range of 5×10^4<Re<5×10^5 using a novel stingmounted sphere apparatus. The roughness element was a circular cylinder, and its width and height was varied to be 1, 2, and 4% of the sphere diameter. At subcritical Re, a lateral force is produced in the direction of the roughness, while at supercritical Re, the force is in the opposite direction. This is caused by asymmetric boundary layer separation, as shown using particle image velocimetry. At supercritical Re, a roughness element that is only 1% the sphere diameter produces a lift to drag ratio of almost one. It was found that the isolated roughness element has the largest effect on the lateral forces when it is located between a streamwise angle of about 40° and 80°. In addition to the mean forces, the unsteady forces were also measured. It was found that at subcritical Re, vortex shedding is aligned to the plane of the roughness element. In addition, the probability distribution of the forces was nearly Gaussian for subcritical Re, but for supercritical Re, the skewness and kurtosis deviate from Gaussian, and the details are dependent on the roughness size. A simple model developed for the vortical structure formed behind the roughness element can be extended to explain aspects of nominally smooth sphere flow, in which external disturbances perturb the sphere boundary layer in an azimuthally local sense. These results also form the basis of comparison for an investigation into the effectiveness of a moving isolated roughness element for manipulating sphere flow.

Numerical modelling of film cooling with and without mist injection

Two-phase CFD calculations, using a Lagrangian model and commercial code Fluent 6.2.16, were employed to calculate the gas and droplet flows and film cooling effectiveness with and without mist on a flat plate. Two different three dimensional geometries are generated and the effects of the geometrical shape, size of droplets, mist concentration in the coolant flow and temperature of mainstream flow for different blowing ratios are studied. A cylindrical and laterally diffused hole with a streamwise angle of 30° and spanwise angle of 0° are used. The diameter of film cooling (d) hole, and the hole length to diameter ratio (L/d) for both of geometries are 10 mm and 4, respectively. Also the blowing ratio ranges from 1.0 to 2.0, and the mainstream Reynolds number based on the mainstream velocity and hole diameter (Red) is 6,219. The results are shown for different droplets diameters (1–10 μm), concentrations (1–5%) and mainstream temperatures (350–500 K). The centreline effectiveness and distribution of effectiveness on the surface of cooling wall are presented.

Numerical simulation of film cooling effectiveness on a flat plate

AbstractNumerical simulation has been conducted to study film cooling effectiveness on a flat plate. Three‐dimensional geometry was generated and the effects of blowing ratio and geometrical shape were studied. A cylindrical round, simple angle (CYSA) and laterally diffused, simple angle (LDSA) hole with a streamwise angle of 30° and spanwise angle of 0° were used. Hole length to diameter ratio (L/D=4) is constant for all geometries. Also the diameter of film cooling hole for different cooling holes at the entrance surface (D=10 mm) is constant. The blowing ratio ranges from 0.5 to 1.67, and the mainstream Reynolds number based on the mainstream velocity and hole diameter (ReD) was 8563. Both local and lateral averaged values are presented. Results have a good correspondence with experimental data obtained by Yuen and Martinez‐Botas (Int. J. Heat Mass Transfer 2003; 46:221–235). The simulation results show that cooling hole shape affects film cooling effectiveness significantly. The LDSA hole decreases the momentum of jet flow at the exit area of the hole and avoids lift‐off phenomenon. Counter‐rotating vortex formed downstream of the hole is weaker for the LDSA hole and secondary flow is not powerful enough to disturb the jet flow structure next to the wall. Also the results show that the LDSA hole has a better lateral coverage due to the diffused shape of the hole and has a higher effectiveness value in a wider region on the wall. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Film cooling characteristics of rows of round holes at various streamwise angles in a crossflow: Part I. Effectiveness

Film cooling effectiveness were studied experimentally on rows of cylindrical holes with streamwise angles of 30°, 60° and 90°, in a flat plate test facility with a zero pressure gradient. Detailed effectiveness and heat transfer results for a single cylindrical hole at the same inclinations have been presented in Yuen and Martinez-Botas [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part I. Effectiveness, Int. J. Heat Mass Transfer 46 (2003) 221–235; C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part II. Heat transfer coefficient, Int. J. Heat Mass Transfer 46 (2003) 237–249] with the same test facility and measurement technique. This present investigation commenced with a single row of holes with two pitch-to-diameter ratios ( p/D) of 3 and 6. It then presents and discusses the effects of introducing inline and staggered rows for each streamwise angle and pitch-to-diameter ratio. The row spacing in the inline and staggered rows is 12.5 diameters in the streamwise direction. The short but engine representative hole length ( L/D = 4) is constant for all geometries. The blowing ratio ranges from 0.33 to 2, and the freestream Reynolds number based on the freestream velocity and hole diameter ( Re D) was 8563. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The current results are compared with the experimental results obtained by other researchers, the effects of the additional inline and staggered rows, and of the variations in injection angle, pitch-to-diameter ratio are described. The objectives of the present study are to provide a consistent set of measurements in terms of effectiveness and heat transfer coefficients presented in the companion paper [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of rows of round holes at various streamwise angles: Part II. Heat transfer coefficient, Int. J. Heat Mass Transfer, in press], obtained systematically with the same test facility, and to deliver a better understanding of film cooling performance. The present results also serve as a database with 105 test cases, in addition to the 21 cases presented in [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part I. Effectiveness, Int. J. Heat Mass Transfer 46 (2003) 221–235], for future numerical modelling.

Film cooling characteristics of rows of round holes at various streamwise angles in a crossflow: Part II. Heat transfer coefficients

Measurements of heat transfer coefficient ( h) are presented for rows of round holes at streamwise angles of 30°, 60° and 90° with a short but engine representative hole length ( L/ D = 4). The study began with a single row of holes with pitch-to-diameter ratios of 3 and 6, followed by two inline and staggered rows for each hole spacing and streamwise inclination, which amount to 105 different test cases in addition to the 21 test cases presented on the single hole [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part I. Effectiveness, Int. J. Heat Mass Transfer, in press; C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part II. Heat transfer coefficients, Int. J. Heat Mass Transfer, in press]. The present investigation is a continuation of the previous work [Yuen and Martinez-Botas, Parts I and II, in press] with the same test facility, operating conditions (freestream Reynolds number, Re D of 8563, and blowing ratio, 0.33 ⩽ M ⩽ 2), and measurement technique of liquid crystal thermography and the steady-state heat transfer method, therefore the results presented in the form of h/ h 0, which is the ratio of heat transfer coefficient with film cooling to that without, are directly comparable. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The corresponding measurements of effectiveness for the rows of holes are presented in a companion paper [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of rows of round holes at various angles in a crossflow: Part I. Effectiveness, Int. J. Heat Mass Transfer, submitted for publication]. The low effectiveness observed with the 90° holes in the companion paper [Yuen and Martinez-Botas, submitted for publication] and the relatively large heat transfer coefficient presented here, suggest that the normal injection should only be used in situations where shallower holes are not feasible. The combined performance of effectiveness and heat transfer coefficient suggests that the two inline rows are likely to be advantageous in the film cooling of turbine blades with good coverage per unit mass flow of cooling air and lower thermal stresses due to the smaller heat load.

Bed load at low Shields stress on arbitrarily sloping beds: Alternative entrainment formulation

According to the Bagnold hypothesis for equilibrium bed load transport, a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical, or threshold, value associated with incipient motion of grains. It was shown in a companion paper [Seminara et al., 2002], however, that the Bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose. An investigation of this failure resulted in a demonstration of its lack of validity even for nearly horizontal beds. The constraint is here replaced with an entrainment formulation, according to which a dynamic equilibrium is maintained by a balance between entrainment of bed grains into the bed load layer and deposition of bed load grains onto the bed. The entrainment function is formulated so that the entrainment rate is an increasing function of the excess of the fluid shear stress at the bed over the threshold value. The formulation is implemented with the aid of a unique set of laboratory data that characterizes equilibrium bed load transport at relatively low shear stresses for streamwise angles of bed inclination varying from nearly 0° to 22°. The formulation is shown to provide a description of bed load transport on nearly horizontal beds that fits the data as well as that resulting from the Bagnold constraint. The entrainment formulation has the added advantage of not requiring the unrealistically high dynamic coefficient of Coulomb friction resulting from the Bagnold constraint. Finally, the entrainment formulation provides reasonable and consistent results on finite streamwise and transverse bed slopes, even those at which the Bagnold formulation breaks down completely.

Interaction of a Streamwise Vortex with an Oblique Shock Wave

Interaction of a supersonic streamwise vortex with an oblique shock wave is considered. A mathematical model of the streamwise vortex is constructed. Three interaction regimes (weak, moderate, and strong) are found. It is shown numerically that vortex breakdown is possible in the case of strong interaction. The influence of the governing parameters on the interaction type is studied. It is shown that the main effect on the interaction type is exerted by the streamwise velocity and angle of the wedge forming the shock wave. The effect of splitting of the primary vortex on the shock wave in the case of moderate and strong interaction regimes is found.

Film cooling characteristics of a single round hole at various streamwise angles in a crossflow: Part II: heat transfer coefficients

Measurements of heat transfer coefficient ( h) are presented for single jets with streamwise angles of 30°, 60° and 90° with a short but engine representative hole length ( L/ D=4). The freestream Reynolds number ( Re D ) is 8563, and the blowing ratio ( M) ranges from 0.33 to 2. The results are presented in the form of h/ h 0 which is the ratio of heat transfer coefficient with film cooling to that without. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The corresponding measurements of effectiveness are presented in a companion paper [C.H.N. Yuen, R.F. Martinez-Botas, Int. J. Heat Mass Transfer, Part I]. In general, only slight variations in h/ h 0 occurred as the blowing ratio was increased with the single 30° hole, in some contrast to the corresponding effectiveness measurements presented in the companion paper [Yuen and Martinez-Botas, Part I]. The single 60° and 90° jets yielded a smaller heat transfer coefficient than the 30° jet.

Film cooling characteristics of a single round hole at various streamwise angles in a crossflow: Part I effectiveness

Film cooling effectiveness were studied experimentally on a cylindrical hole with a streamwise angle of 30°, 60° and 90°, in a flat plate test facility with a zero pressure gradient. The short but engine representative hole length ( L/ D=4) is constant for all three geometries. The blowing ratio ranges from 0.33 to 2, and the freestream Reynolds number based on the freestream velocity and hole diameter ( Re D) was 8563. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The current results are compared with the experimental results obtained by other researchers, and the effects of variations in injection angle are described. There is not a single study on film cooling performance of a single round hole at the three streamwise angles for a wide range of blowing ratios with a short hole length. Therefore, the objective of the present study is to provide a consistent set of measurements in terms of effectiveness and heat transfer coefficients [Int. J. Heat Mass Transfer, 2002] obtained systematically on a flat plate, and to deliver a better understanding of film cooling performance, with explanations deduced from the existing knowledge of a single jet in crossflow, before more engine representative conditions are introduced. The present results also serve as a database for future numerical modelling.

Effect of compound angle injection on flat surface film cooling with large streamwise injection angle

Film cooling measurements are presented over a flat surface through a single row of discrete holes angled 55° along the streamwise direction. The holes are angled 0° and 60° in the lateral direction to study the effect of compound angle injection. Detailed heat transfer coefficient enhancement and film effectiveness distributions are presented for the entire region from downstream of the holes to distances far downstream at about X/d=20. Tests were conducted in a low speed wind tunnel. The mainstream flow Reynolds number based on hole diameter is around 9500 and the free-stream turbulence intensity is set at 11%. Results are presented for three blowing ratios of 0.5, 1.0, and 1.5 and a coolant-to-mainstream density ratio of 1.0. A transient liquid crystal technique will be used to measure both the local heat transfer coefficient and film effectiveness results simultaneously. The technique uses two similar tests to resolve the heat transfer coefficient and film effectiveness. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet–mainstream interactions for different hole orientations with large streamwise angle injection. Results show that adding a compound angle to a hole with large streamwise angle produces significant variations in the detailed film effectiveness distributions and enhances local heat transfer coefficients.