Koji Miyaji

Enhancement of the leading-edge separation vortices by trailing-edge lateral blowing

The numerical simulations were carried out for the study of trailing-edge lateral blowing for the delta wing

An efficient correction procedure via reconstruction for simulation of viscous flow on moving and deforming domains

In this paper, we report the development of a new parallel solver using the Correction Procedure via Reconstruction (CPR) for viscous flows on moving and deforming grids. By employing an accurate treatment of flux derivatives for moving and deforming unstructured grids consisting of all quadrilateral cells, it is found that the Geometric Conservation Law is not explicitly required, the free-stream preservation is automatically satisfied. The CPR code is verified using a benchmark case for a moving inviscid vortex on moving and deforming grids. The optimal orders of accuracy are obtained. It is subsequently employed to study viscous flows on moving and deforming grids. The CPR method is faster than and nearly as accurate as the SD method for solving viscous flow problems with moving boundaries.

Computational Study on Effect of Synthetic Jet Design Parameters

Effects of amplitude and frequency of synthetic jet on the characteristics of induced jet are investigated. To estimate effects of the parameters, flow inside the synthetic jet cavity and orifice and the outer flow is simultaneously simulated using large-eddy simulation (LES). Comparison of the present LES result with the experimental data shows that three-dimensional LES of the flow inside the cavity is essential for accurate estimation of the velocity and velocity fluctuation of the synthetic jet. Comparison of the present results under various flow conditions shows that amplitude and frequency can control profiles of time-averaged vertical velocity and fluctuation of the vertical velocity as well as damping rate of the induced velocity and fluctuation.

Computational Analysis of Vortex Structures Induced by a Synthetic Jet to Control Separated Flows

The vortex structure of a separated flow over a backward-facing step controlled by a synthetic jet is investigated by using an implicit large-eddy simulation with a high-order compact difference scheme. The computation results show that mixing in the shear layer is not enhanced, when the flow is controlled at the normalized frequency of 2.0 based on the height of backward-facing step. In this case the separation length is similar to that in the case without flow control because weak and short periodic vortices are induced by the synthetic jet, and they weakly interact with the shear layer and diffuse in the recirculation region. On the other hand, the separation length becomes 20% shorter when the flow is controlled at F+h = 0.2 than that in the case without flow control. Strong two-dimensional vortices generated from the synthetic jet interact with the shear layer, which increases the periodic component of the Reynolds stress within that layer. These vortices are deformed into three-dimensional structure...

Transitional flow over a SD7003 wing using flux reconstruction scheme

This paper focuses on the verification of the ability of a high-order flux reconstruction scheme to perform implicit large eddy simulation of the transitional flow with a laminar separation bubble. The numerical simulations are performed on the SD7003 wing section at angles of attack 4◦ and 8◦ at low-Reynolds number Re = 60, 000. The averaged and statistical results are obtained using the 3, 4-order accurate FR code on two computational domains. The calculated results are discussed and compared with the literature. Despite of a fairly coarse grid resolution a remarkable agreement with results obtained with much finer LES simulations has been achieved.

On the Compressible Flow Simulations with Shocks by a Flux Reconstruction Approach

A high-order accurate flow solution method for quadrilateral elements is developed and tested. The method employs the flux reconstruction (FR) approach proposed by Huynh. Ideal orders of accuracy are achieved for several problems on structured-based grids while some deterioration is observed on purely unstructured grids. Cares for curved wall boundary are also shown. The localized artificial diffusivity (LAD) method is incorporated to capture discontinuities that is crucial for compressible flow simulations. The FR+LAD works very well for 1D test cases but multi-dimensional shock problems requires further modifications to confine the artificial diffusivity to the shock location. Hybrid scheme of the FR and finite difference method taking advantage of 1D-feature alleviates the instability. I. Introduction Expanding demands for the computational fluid dynamics (CFD) requires more reliable numerical schemes. Specifically, turbulent flow simulations, acoustic simulation, combustion simulations and their combined problems. The key words in such simulations may be high accuracy and high resolution. In structured grid CFD, a compact finite difference scheme satisfies both requirements at higher level than existing other methods. If we put more emphasis on easier handling of complex geometries and flow-data dependent grid generation (grid adaptation), then unstructured grid method should also be explored and it should depart from 2nd-order scheme with limiter. Recent efforts in this area are development of the discontinuous Galerkin (DG) method, 1,2 the spectral finite volume (SV) method 3 and the staggered-grid multi-domain method spectral finite difference (SG) method 4,5 and its evolutional method called a spectral difference method. 6 The common and maybe the only way for those unstructured methods is to add degrees of freedom in each cell to achieve high order since the wide stencil of the original grid is not possible due to unstructured nature. The ENO-type method that uses original degrees of freedom in the grids and extends adaptive stencils to the flow solutions is also explored but the difficulty of extending stencils due to undirectional nature of unstructured grids and the unsuitability for parallel computing prohibits wide applications. A flux reconstruction (FR) scheme 7,8 studied in the paper is the new one among the former group. It uses differential form of conservation laws like the SD method but it is more general and includes equivalent counter part of the schemes in the group. In this paper, the performance of the FR is tested by a newly developed Navier-Stokes solver. Realistic flow applications of the FR in the Navier-Stokes equations are seldom seen since it is relatively new scheme. The Localized artificial diffusivity (LAD) 9–13 is incorporated for the shock capturing in the FR. The last item is motivated by the challenge and success of combining the SD and LAD in the recent study. 11,12 Wang 14 developed the lifting collocation penalty (LCP) method to extend the FR to triangular or tetrahedral grids and applied the LCP-FR combined method for hybrid unstructured grids. In the present study, only quadrilateral cells are treated to directly apply the LAD method that was developed on structured grids. The shock capturing by the FR+LAD high order scheme is tried.

Numerical analysis of three-dimensional shock/shock interactions and the aerodynamic heating

Three-dimensional interactions of an obliqueand a bow-shock wave at hypersonic speeds are numerically simulated using Navier-Stokes equations. Unstructured solution adaptive g,rids with h,ybrid cell configurations are used to accurately predict both the interaction pattern and the aerodynamic heatiqg. Two incident shock conditions are examined and the results are compared with a two-dimensional typeIV flow. The computed flows show three-dimensional complicated structures and they are well explained by examining the interaction flows in appropriate cross sections, whe,re well-investigated twodimensional interactions serve to understand the flow. In both three-dimensional cases, it is commonly said that a locally two-dimensional typeIV appears when a shock impinges around the stagnation region behind the bow shock wave. Other types simultaneously appear depending on the location of the impinging shock wave. A simple method to predict the three-dimensional interaction flow configurations is considered from the obtained results. The heat flux increases due to the impingement of the supersonic jet in both cases. The increments are much smaller than that of’ the two-dimensional typeIV because a strong jet bow shock is not generated in the threedimensional cases.

Aerodynamic design of Balloon-based operation vehicle for precooled turbojet engine demonstration

The Balloon-based Operation Vehicle (BOV) originally developed for the micro-gravity experiments is modified as a supersonic flight demonstrator of a sub-scale precooled turbojet engine developed in Japan Aerospace Exploration Agency. In the supersonic flight demonstration, the vehicle is raised by a high-altitude balloon up to a 40 km altitude and dropped to accelerate the vehicle to a supersonic velocity. To extend the flight time for an engine combustion test in the supersonic environments, the vehicle is redesigned in a wingbody configuration with a main delta wing and movable vertical and horizontal tail wings so that it can be pulled up above an altitude of 5 km. As a result, the vehicle is capable of reaching the maximum flight Mach number of 2 with the dynamic pressure of 25 kPa at an altitude of 17 km, realizing the engine test time longer than 30 sec. The flight demonstration is currently scheduled in 2009. In this article, an overview of the aerodynamic characteristics of the flight demonstrator and the flight trajectory plan is presented.

High-lift devices for a delta wing installed around a trailing-edge

Three devices to improve the aerodynamic characteristics of a delta wing at low speeds and high angles of attack are computationally examined. These are two types of blowing at the trailing edge and a slotted flap. All three are commonly employed on rectangle wings. They all show favorable effects, namely, chordwise blowing increases the lift considerably. The effectiveness in strengthening the leading-edge vortex is higher for chordwise blowing than lateral blowing. It is observed that, although the jet slots are installed at a trailing edge, the blowing strengthens the leading-edge separation vortex over the delta wing. This motivated an investigation of the use of a slotted flap. The flap also increases the lift of the wing, as well as the total lift due to both the wing and the flap, but the effect on the leading-edge vortices is smaller than both types of blowing

Computational Study of Frequency and Amplitude Effects on Separation Flow Control With the Synthetic Jet

In order to investigate the frequency and amplitude effects of the synthetic jet on the flow field, numerical simulation is carried out. Even though the final objective of this study is to understand mechanism of separation control for various objects, streamline and bluff bodies, the configuration of backward-facing step is chosen as the first step because of the simplicity. Three-dimensional Navier-Stokes equations are solved. Implicit large eddy simulation using high-order compact difference scheme is applied. The present analysis is addressed on the frequency characteristics of the synthetic jet for understanding frequency characteristics and flow-filed. Three cases are selected, No-control, F+ h = 0.2 and F+ h = 2.0, where non-dimensional frequency F+ h is normalized with the height of backward-facing step and the free stream velocity. The present computation shows that at F+ h = 2.0, separation length is 20 percent shorter than the No-control case. Strong two-dimensional vortices generated from the synthetic jet interact with the shear layer, which results in the increase of the Reynolds stress in the shear layer region. These vortices are deformed into three-dimensional structures, which make Reynolds stress stronger in the recirculation region. At F+ h = 2.0, size of the separation length is almost same as the No-control case because the mixing between the synthetic jet and the shear layer is not enhanced. Weak and short periodic vortices induced from the synthetic jet do not interacts with the shear layer very much and diffuse in the recirculation region.© 2009 ASME