Vector Control of Synthetic Jets Using an Asymmetric Slot

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Ryota Kobayashi ◽  
Koichi Nishibe ◽  
Yusuke Watabe ◽  
Kotaro Sato ◽  
Kazuhiko Yokota
Keyword(s):  
Cross Section ◽  
Rigid Wall ◽  
Synthetic Jets ◽  
Dimensionless Frequency ◽  
Fundamental Study ◽  
Recirculation Flow ◽  
Projection Length ◽  
Wire Method ◽  
Nozzle Shape ◽  
Flow Visualizations

This paper presents a fundamental study on jet vectoring control by adjusting the dimensionless frequency of synthetic jets over time without changing the injection nozzle shape in actuators. This work involves the introduction of asymmetric slots with various sharp projection lengths in free synthetic jets for various actuator frequencies. The influences of the dimensionless parameters, sharp projection length C, and actuator frequency f* on the behavior of free synthetic jets are experimentally investigated under the same slot width b and Reynolds number Re = 990, and numerical simulations are performed to supplement these experiments. Furthermore, the behavior of synthetic jets is compared with that of continuous jets. The measurements of the velocities for both jet types are performed for the flow visualizations to observe the jet behaviors obtained using the smoke-wire method. The typical flow patterns and the time-averaged velocity distributions of the synthetic jets for various sharp projection lengths and dimensionless frequencies are demonstrated through the experiment. The influence of the dimensionless frequency on the stagnation point near a rigid wall when the inclined synthetic jets form a recirculation flow is also investigated. Furthermore, the degree of the bend of the jets is evaluated based on the change in the jet center's position at a reference downstream cross section. The results show that the jet direction of the synthetic jets induced by the asymmetric slots is related to both the dimensionless sharp projection length and the dimensionless frequency.

Vector Control of Synthetic Jets Using an Asymmetric Slot

2016 ◽  
Author(s):  
Ryota Kobayashi ◽  
Koichi Nishibe ◽  
Yusuke Watabe ◽  
Kotaro Sato ◽  
Kazuhiko Yokota
Keyword(s):  
Strouhal Number ◽  
Shape Change ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Fundamental Study ◽  
Wire Method ◽  
Number Frequency ◽  
Beak Length

This is a fundamental study on the jet vectoring control by means of adjusting the synthetic jet Strouhal number (frequency) without slot shape change with time in actuators. This work involved introduction of asymmetric slots with various beak lengths in free synthetic jets for various frequencies, experimentally and numerically. Furthermore, the behavior of synthetic jets was compared with that of the continuous jets. In our experiment, velocity measurements for both types of jets were performed using a hot-wire anemometer with an I-type probe and a traverser, and flow visualization for observing the behavior of the jets was performed using the smoke wire method. Through the experiment, typical flow patterns and time-averaged velocity distributions of synthetic jets for various beak lengths and Strouhal number were demonstrated. The time-averaged velocity was measured at a reference point on the slot centerline to evaluate the degree of the bend of the jets and the obtained data was used in the Strouhal number-beak length map.

RECOMPRESSION PHENOMENA IN STEAM NOZZLES: PART I

1941 ◽  
Vol 19a (5) ◽  
pp. 67-85 ◽  
Author(s):  
Charles Alexander Robb
Keyword(s):  
Cross Section ◽  
Inlet Pressure ◽  
Flowing Fluid ◽  
Vena Contracta ◽  
Venturi Effect ◽  
Change Of State ◽  
Expansion Curve ◽  
Nozzle Shape ◽  
The Difference ◽  
Load Conditions

The purpose of the investigation was to find when and how recompression occurs in the flow of steam through a nozzle, its causes and effects, how the results can be predicted, and what losses are caused by these phenomena. Four types of recompression were observed: equilibrium, latent, vena contracta, and shock recompression.It is shown that steam in flowing through a nozzle of varying cross-section responds to the changes of area within certain limits and recompression phenomena may be expected. The Venturi effect has been observed in single nozzles, and in both parts of a composite nozzle.The behaviour of steam in equilibrium recompression in convergent-divergent nozzles can be predicted by means of an equation from which a valuers obtained for the pressure pr at which overexpansion ends and an increase in pressure begins; the pressure pr depends on the inlet pressure to the nozzle and on the difference in pressure at inlet and outlet.The recompression due to the contraction of the section can be controlled and avoided by suitable provision in the design. The compression following a change of state of a flowing fluid can be controlled by adjusting the rate of expansion of the fluid in specified pressure ranges. Novel evidence of latent recompression is found in a break or notch in the pressure expansion curve plotted from search tube observations.The experiments were carried out at inlet pressures within the range at which turbine-condition curves may cross the saturation line between the superheat and wet regions on the Mollier diagram, and the effects of recompression to be expected under varying load conditions can be interpreted for particular nozzle designs.Comparative studies of the effect of the nozzle shape on recompression phenomena and the losses resulting therefrom have indicated that the conditions for favourable efficiency require a larger inlet radius at the throat and a length shorter than the lengths commonly found in practice.

Study on the Flow Characteristics of Synthetic Jets Near a Rigid Plane Boundary

2011 ◽  
Author(s):  
Ryota Tsunoda ◽  
Koichi Nishibe ◽  
Yuki Fujita ◽  
Kotaro Sato ◽  
Kazuhiko Yokota ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Plane Boundary ◽  
Jet Flows ◽  
Rigid Boundary ◽  
Wire Method ◽  
Rigid Plane

The jet flows have been applied to various fields to control the flow separation. Over the last decade, several studies have investigated synthetic jets. However, there are still many clarifications needed, including details of the structure and Coanda effect of synthetic jets. The present study clarifies some fundamental flow characteristics of free synthetic jets and synthetic jets near a rigid boundary by conducting an experiment and numerical simulations. As the main results, it is found that the velocity distribution of free synthetic jets depends on K = Re/S2 (the ratio of the Reynolds number to the square of the Stokes number) and can be identified by the maximum velocity at the centerline and the jet half-width. Flow visualization is carried out applying the smoke wire method. In addition, it is confirmed that the flow characteristics of the synthetic jet near a rigid boundary and re-attachment length of the synthetic jet are determined not only by H1/b0 (normalized step heights) but also K.

Collapse study of thin-walled polygonal section columns subjected to oblique loads

2007 ◽  
Vol 221 (7) ◽  
pp. 801-810 ◽  
Author(s):  
P Hosseini-Tehrani ◽  
S Pirmohammad
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Rigid Wall ◽  
Point Of View ◽  
Explicit Finite Element ◽  
Thin Walled ◽  
Oblique Load ◽  
Crash Behaviour ◽  
Vehicle Crashworthiness ◽  
Load Conditions

The present paper deals with the collapse simulation of aluminium alloy extruded polygonal section columns subjected to oblique loads. Oblique load conditions in numerical simulations are applied by means of impacting a declined rigid wall on the tubes with no friction in this task. The explicit finite element code LS-DYNA is used to simulate the crash behaviour of polygonal section columns that are undergoing both axial and bending collapse situations. In order to validate LS-DYNA results the collapse procedure of square columns is successfully simulated and the obtained numerical results are compared with actual available experimental data. Mean crush loads and permanent displacements corresponding to load angles have been investigated, considering columns with square, hexagonal, octagonal, decagonal, and circular cross-sections. It is shown that the octagonal cross-section has better characteristics from the point of view of vehicle crashworthiness under oblique load conditions.

Recirculation Flow of Nanofluid Through Periodic Nanotube with Hexagonal Cross-Section

2020 ◽  
Vol 12 (2) ◽  
pp. 147-155
Author(s):  
Md. Nazmul Hasan ◽  
Asif Mahmud ◽  
Md. Shakhaoath Khan ◽  
Md. Azmol Huda ◽  
Nazmul Islam
Keyword(s):  
Cross Section ◽  
Recirculation Zone ◽  
Geometric Parameters ◽  
Governing Equations ◽  
Throat Radius ◽  
Recirculation Flow ◽  
Hexagonal Cross Section ◽  
Recirculation Zones ◽  
Flow Through ◽  
Fortran 90

In this paper, we have investigated the recirculation flow of a nanofluid in the developed flow zones of an infinite periodic nanotube with a hexagonal cross-section. A numerical analysis is commenced to identify the existence of single and double recirculation zones for various geometric parameters. The boundary element method (BEM) has been formulated for an unbound interim nanotube for solving the governing equations. We have developed the codes for the BEM method in FORTRAN 90, and the graphs have been plotted in MATLAB 2016. We have various geometric parameters to inaugurate circumstances for the onset of recirculation. We have found recirculation flow through this type of periodic tube for a set of geometric parameters such as amplitude, wavelength and throat radius etc. Firstly recirculation flow in the expansion region of the nanotube is prophesied to arrive beyond a critical amplitude and second order recirculation zone is also predicted for still higher amplitudes. The recirculation flow has great importance in the application, for example, it can be used in the particle separation process.

Vortex excitation of prisms with elongated rectangular, H and [vdash ] cross-sections

1986 ◽  
Vol 163 ◽  
pp. 149-169 ◽  
Author(s):  
Yasuharu Nakamura ◽  
Masamichi Nakashima
Keyword(s):  
Shear Layer ◽  
Cross Section ◽  
Cross Sections ◽  
Shear Layers ◽  
Water Tank ◽  
Shear Layer Instability ◽  
Flow Measurements ◽  
Trailing Edges ◽  
Rear Part ◽  
Flow Visualizations

This is an experimental investigation of vortex excitation of prisms with elongated rectangular, H- and [vdash ]-shaped cross-sections, where the depth parallel to the flow is much greater than the height perpendicular to the flow. Measurements are made of free oscillations in a wind tunnel and flow visualizations in a water tank. The flow around elongated bluff prisms is dominated by the impinging-shear- layer instability where the separated shear layers become unstable in the presence of different kinds of shape of the rear part of the cross-section, which may include sharp trailing edges. The two unstable shear layers interact with each other when they meet together downstream of the prism, thereby forming Kármán vortices with the same frequency of oscillation. The former impinging-shear-layer instability is largely responsible for vortex excitation of elongated bluff prisms.

Prediction of the Temperature in a Long Horizontal Fin Rod Cooled by Natural Convection and Radiation

2004 ◽  
Author(s):  
Donald W. Mueller ◽  
Hosni I. Abu-Mulaweh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Elevated Temperature ◽  
Heat Loss ◽  
Cross Section ◽  
Radiative Heat ◽  
Horizontal Cylinder ◽  
Physical Situation ◽  
Fundamental Study ◽  
Finite Difference Formulation

The objective of this fundamental study is to numerically predict the temperature along a fin cooled by natural convection and radiation and to compare with measurements. The physical situation considered is a horizontal fin with a cylindrical cross-section. One end of the fin is maintained at a constant elevated temperature, and the fin is sufficiently long so that heat loss from the tip is negligible. Heat is transferred by conduction along the fin and dissipated from the surface via natural convection and radiation. The effect of natural convection is described with a published correlation for a horizontal cylinder, and a simple model is used for the radiative heat transfer. A finite difference formulation that allows for variable fluid property effects is used to determine the temperature distribution along the fin. A comparison is made to experimental results, and the agreement between the model and experiment is very good. Results show that the heat loss due to radiation is typically 15%–20% of the total.

Study on Flow Around a Rectangular Cylinder With an Asymmetric Slot for Synthetic Jets

2016 ◽  
Author(s):  
Nobuhiro Kobayashi ◽  
Koichi Nishibe ◽  
Yusuke Watabe ◽  
Kotaro Sato ◽  
Kazuhiko Yokota
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Large Scale ◽  
Rigid Wall ◽  
Synthetic Jets ◽  
Asymmetric Flow ◽  
Stroke Length ◽  
Rectangular Cylinder ◽  
Upstream Direction ◽  
Control Fluid

Several recent studies have examined the fundamental behavior of synthetic jets as substitutes for continuous jets [1–4]. In addition, attempts to control fluid machines with synthetic jets have also begun [5, 6]. However, little attention has been given to the effects of an asymmetric flow field on the behavior of synthetic jets [7, 8]. There have been few reports on the influence of a large-scale asymmetric boundary on the motion of synthetic jets [7]. In this study, an attempt was made to describe the flow around a rectangular cylinder with an asymmetric slot for synthetic jets. The main results are as follows: (1) the continuous jets proceed toward the nearest rigid wall by the Coanda effect independently of the slot geometry (with/without beak), (2) when the nondimensional stroke of the synthetic jets is large, the flow patterns are similar to those of continuous jets, (3) when the nondimensional stroke is small and the rectangular cylinder is placed near the wall opposite the side of the beak, the synthetic jets turn to the upstream direction under the present range of conditions, and (4) the flow rate in the duct depends on the non-dimensional stroke length when the rectangular cylinder is placed near the wall opposite the side of the beak.

Numerical Investigation of Hollow Metal Cross Section Profiles on Impact

2011 ◽  
Vol 383-390 ◽  
pp. 3241-3248 ◽  
Author(s):  
Waluyo Adi Siswanto ◽  
Badrul Omar ◽  
Shamsir Shukri
Keyword(s):  
Open Source ◽  
Numerical Investigation ◽  
Cross Section ◽  
Cross Sections ◽  
Open Source Software ◽  
Rigid Wall ◽  
Axial Mode ◽  
Hexagonal Shape ◽  
Vehicle Structure ◽  
Hollow Metal

A front bumper of a car is attached to the main vehicle structure by using hollow metals. This paper investigates various cross section profiles that can be used as bumper attachments. Several cross section profiles with the same circumscribe are firstly selected, i.e. round, square, triangular and hexagonal shape cross sections. Each model is then numerically impacted in an axial mode as if it is crashed into a rigid wall with an impacting velocity of 10 m/s or equivalent to 36 m/s. A dynamic-explicit open source software Impact is employed to do the simulation. The displacement results are monitored in the first 1:8ms then compared to the models that can absorb better showing the less displaced in certain examination nodes. The results shows that the triangle cross section performs better compared to other cross sections.

Sign in / Sign up

Export Citation Format

Share Document