2-D Modeling of Nonlinear Dynamics of Forcespinning Jet Formation

Forcespinning is a novel method that makes use of centrifugal forces to produce nanofibers rapidly and at high yields. To improve and enhance the forcespinning production method, a 2D computational forcespinning inviscid fluid dynamics model is developed. Two models, namely time-independent and time-dependent, are obtained in order to investigate the influence of various parameters on fiber forcespinning formation (trajectory, jet diameter, tangential velocity). The fluid dynamics equations are solved using the method of multiple scales along with the finite difference method, and including slender-jet theory assumptions. It is important to produce jets with small diameters in the micro- and nano-range. The Weber (We) and Rossby (Rb) numbers were found to both expand the jet trajectory as they increased. Increasing We and/or decreasing Rb was found to decrease the jet diameter. Also, by varying forcespinning parameters, it has been found that the jet radius can be decreased by increasing the jet exit angle in the direction of rotation, reducing the spinneret fluid level, increasing the angular velocity of the spinneret, reducing spinneret length, and/or reducing the orifice diameter. Knowing the jet trajectories is important for designing and positioning of fiber collector. It has been found that the trajectories expand out with the increase of the jet exit angle in the direction of rotation, increase of fluid level, increase of angular velocity, and/or increase of the spinneret length. Production rates and jet radii for any predetermined radial collector distance were also determined.

Numerical Assessment of an Air Cleaner Device under Different Working Conditions in an Indoor Environment

Transmission and spread of exhaled contaminants in the air may cause many airborne infectious diseases. In addition to appropriate ventilation, air cleaner devices are used as one of the most common ways to improve the indoor air quality. Therefore, it is necessary to understand the performance of an air cleaner under different operating conditions. This study mainly concerns investigating the effect of presence or absence of furniture and its displacement on the removal rate of the particles leaving a person’s mouth while coughing in an isolated room. Moreover, the effect of air exit angle of the device on removal rate of contaminated particles and the pattern of their dispersion within a room was studied. To this aim, computational fluid dynamics were employed to examine the mentioned effects by using the Eulerian− Lagrangian method. As the results indicated, when the furniture was placed farther away from the device, more particles were removed by the device. Additionally, the air ejection angle of the air cleaner device significantly affects the removal of particles. Results of the present study could improve use of air cleaner devices for maximum reduction of particles in the indoor environment.

Analysis of the Exit Flow Angle and Characteristics of Flow in Axial Turbine Cascades

Despite a wealth of sophisticated CFD-methods, most designs are still based on one-dimensional and two-dimensional inviscid analytical tools. In such methods, realistic loss and angle assessment are indeed critical in order to arrive at correct loading, flow coefficient and reaction. The selected values are normally retained through the detailed design sequence for each iteration. This means that the throat sizing and hence the gauge angle is largely based on the early design work within the through-flow environment. Even one-degree error in angle estimation will turn into a rather large capacity error. For most designs, the exchange rate between capacity and gauge angle is on the order of 3–5 percent, per degree exit angle. In a previous publication, a methodology and equations were presented to assess the exit flow in an axial turbine blade row by Mamaev in Russian nomenclature and the tangential coordinate system. The approach, provided a unified and flow-physics based method for assessing exit angles from the geometry features like gauge angle, uncovered turning and flow features like Laval number, etc. Analysis of those formulas showed good agreement with physical flow pattern in real cascades for sub and transonic blade cascades. In this work, the same basic principal procedure is followed by employing the more international agreed nomenclature of blades such as an axial reference plane and Mach number. In the current work, the one-dimensional analysis results were compared with the three dimensional numerical modelling of a full annulus two-stage turbine. Analysis of the results showed the inherent unsteadiness specially outside the rotor blade cascades, however, comparison of the mass averaged exit angle with the one dimensional analysis showed satisfactory agreement.

Aerodynamic Design Aspects for Stator of Highly Loaded Tandem Bladed Axial Compressor

Tandem bladed axial compressors prove to be a promising way of increasing the total pressure rise capability per stage with acceptable losses. The practical use of tandem bladed systems has been limited to IGVs and stators especially for highly loaded compressor stages used in gas turbine engine applications. Looking to the benefits of the tandem bladed compressor stage, more research activities are focused to explore possibilities of tandem bladed compressor rotor for core stages of a gas turbine engines these days. The main purpose of the stator is to remove the swirl from the flow coming out from the rotor and more often it is accompanied by flow diffusion using stator passage based on design criteria. The whole idea and motivation for a tandem bladed rotor are to provide a very high fluid deflection in order to achieve a higher total pressure rise. The extreme flow turning imparted by a tandem bladed rotor has to be handled by the stator with minimum losses. For an axial entry and axial exit compressor without IGVs, this results in high blade curvature for the stator. The present study investigates the design challenges of such stator for a tandem bladed rotor handling an average flow turning of 58.87° and diffusion factor (DF) of 0.66. The flow field at the tandem-rotor passage exit is highly three-dimensional in comparison to a conventional rotor. The tip leakage flow from both the rotor blades interacts with the shroud boundary layer resulting in intense mixing losses and flow blockage. Also, the highly loaded rotor blades shed two strong trailing edge wakes which merge to form a thicker wake at the rotor exit plane. This gets coupled with flow blockage associated with rotor tip clearance flow and shroud boundary layer. Together these two phenomena result in a highly three-dimensional velocity field fed to the stator leading edge. The flow blockage at the exit of the rotor passage especially near the tip region results in a region of momentum deficit fluid near the stator LE. This implies that stator needs to have high incidence tolerance to accommodate such an incoming flow. This required specific changes in the shape of the stator blade near the tip region to accommodate this momentum deficit flow. Interestingly the air exit angle from the aft blade is influenced by trailing edge wake from front blade changing the overall rotor exit angle. It is interesting to note that the conventional stator design strategies do not suffice for a tandem rotor-stator combination due to the aforementioned inherent three-dimensionalities. The air inlet angle for stator has to be recalculated from the average air exit angles from the fore and aft blade respectively along the span. The mesh generation for tandem rotor-single stator stage was done using ANSYS TurboGrid® and the simulations were performed using commercial package ANSYS CFX® 18.0. The current study demonstrates a more robust design approach for the stator incorporating controlled chord-wise flow turning along the span, resulting in a favorable flow passage shape variation along the span. The systematic design approach combined with modifications in profile shape and blade stacking results in a three-dimensional blade shape for stage design. The paper will explore more on the untouched approach and challenges for such future tandem bladed axial flow compressor stages.

Modelling of Vane and Rotor Blade Rows in Simulations of Gas Turbine Performance

A method of modelling of nozzle and rotor blade rows of gas turbine dedicated to simulations of gas turbine performance is proposed. The method is applicable especially in early design stage when many of geometric parameters are yet subject to change. The method is based on analytical formulas derived from considerations of flow theory and from cascade experiments. It involves determination of parameters of gas flow on the mean radius of blade rows. The blade row gas exit angle, determined in turbine design point is a basis for determination of details of blade contour behind the throat position. Throat area is then fixed based on required maximum mass flow in critical conditions. Blade leading edge radius is determined based on flow inlet angle to the blade row in the design point. The accuracy of analytical formulas applied for definition of blade contour details for assumed gas exit angle was verified by comparing the results of analytical formulas with CFD simulations for an airfoil cascade. Losses of enthalpy due to non-isentropic gas flow are evaluated using the analytical model of Craig and Cox, based on cascade experiments. Effects of blade cooling flows on losses of total pressure of the gas are determined based on analytical formulas applicable to film cooling with cooling streams blowing from discrete point along blade surface, including leading and trailing edges. The losses of total pressure due to film cooling of blades are incorporated into the Craig and Cox model as additional factor modifying gas flow velocities.

Effects of Nozzle Exit Angle on the Pressure Characteristics of SRWJs Used for Deep-Hole Drilling

The self-resonating waterjet (SRWJ) has been applied in petroleum, natural gas, and mining engineering ever since its strong erosion ability in deep-hole drilling was recognized. Aiming at further improving the working efficiency of SRWJs, the effects of the exit angle of the organ-pipe nozzle on the axial pressure oscillations of the jet were experimentally studied. Six exit angles of θ = 0°, 30°, 45°, 60°, 75°, and 90° were employed in the experiment, and the axial pressure oscillation peak (Pmax) and amplitude (Pa) were used for characterizing the performance of SRWJs. It was found that the exit angle greatly affects the axial pressure oscillations, including the development trends against the standoff distance and the magnitudes of Pmax and Pa. Under testing with two inlet pressures, the exit angle of θ = 0° always resulted in the greatest Pmax and Pa within the range of the testing standoff distance. With the increase of standoff distance, both Pmax and Pa first increased and then decreased when the exit angle was 0°; while they kept decreasing when the exit angle was 30°, 45°, 60°, 75°, and 90°. Moreover, the exit angles of θ = 90° and 60°, corresponding to inlet pressures of Pi = 10 MPa and 20 MPa, led to both the minimum magnitudes of Pmax and Pa under the experimental conditions. The results also indicate that the exit angle affects the interactions between the nozzle lip and the jet and help provide information for improving the working efficiency of SRWJs in practical applications.