Experimental study of vortex flows over delta wings in wing-rock motion
Explore the source record for details and available documents.
Ng, T. T.↗
Engineering topics
Ng, T. T.
Publications and source records attributed to Ng, T. T..
Forebody vortex control using small, rotatable strakes
Explore the source record for details and available documents.
Ng, T. T.↗
Forebody vortex control with miniature, rotatable nose-boom strakes
Experiments have been conducted in water and wind tunnel facilities to investigate the effectiveness of using rotatable miniaturized forebody nose-boom strakes to manipulate and control fighter aircraft forebody vortices at moderate to high angles of attack to provide potential aerodynamic control power in yaw. Water tunnel tests including flow visualization and yaw moment measurements were conducted on several different models of the F-16 fighter. Wind tunnel force and moment tests investigated the effects of several nose-boom strake configurations on an isolated 1/8th-scale X-29A forebody model. The primary variables of interest were strake size, configuration and roll angle orientation on the nose-boom. Both experiments showed clearly that small nose-boom strakes can be very effective in controlling the forebody vortex flowfield. Different degrees of flow asymmetry can be obtained by rotating a single or a pair of small strakes located on the nose-boom. With large fixed forebody strakes, such as those on the X-29A configuration, the effectiveness of the nose-boom strakes is significantly reduced.
Suarez, Carlos J.↗
Wing rock suppression using forebody vortex control
Static and free-to-roll tests were conducted in a water tunnel with a configuration that consisted of a highly-slender forebody and 78-deg sweep delta wings. Flow visualization was performed and the roll angle histories were obtained. The fluid mechanisms governing the wing rock of this configuration were identified. Different means of suppressing wing rock by controlling the forebody vortices using small blowing jets were also explored. Steady blowing was found to be capable of suppressing wing rock, but significant vortex asymmetries had to be induced at the same time. On the other hand, alternating pulsed blowing on the left and right sides of the forebody was demonstrated to be potentially an effective means of suppressing wing rock and eliminating large asymmetric moments at high angles of attack.
Ng, T. T.↗
Forebody vortex control as a complement to thrust vectoring
The desire to enhance the controllability of fighter aircraft at high angles of attack, particularly yaw control, has fostered an interest in both vectored thrust and active control of forebody vortices. This paper reviews several methods of forebody vortex control that have been investigated with water and wind tunnel tests of both generic and actual fighter configurations. The methods investigated include pneumatic or blowing techniques using surface-mounted jets and slots, surface suction, variable-height deployable strakes, and rotatable tip strakes. Flow visualization, and force and moment measurements have shown that all of the methods are effective in manipulating the forebody vortices over a wide range of angles of attack and sideslip, primarily through control over flow separation on the surface of the forebody. All are most effective when applied near the forebody tip. The advantages and limitations of the various methods are reviewed.
Malcolm, G. N.↗
Seven hole probe measurement of leading edge vortex flows
This paper discusses the use of a seven-hole probe on measurements of leading edge vortices of highly sweep delta wing planforms. Intrusive probe data taken with the pressure probe were compared with nonintrusive measurements made with laser Doppler anemometry system. In addition to probe size, the natural position of breakdown and the sweep angle of the wing are also factors in determining sensitivity of the flow to probe interference. At low angles of attach vortex breakdown does not occur in the vicinity of the model and the seven hole probe was found to yield reasonably accurate measurements. When the angle of attack of the model was increased so that vortex breakdown was near the trailing edge, introducing the probe over the wing would cause the breakdown position to move ahead of the probe. However, when breakdown naturally occurred ahead of the mid-chord of the wing the vortices were found to be less sensitive to a probe placed behind the breakdown point. Vortex breakdown on a lower swept wing is found to be more sensitive to interference. Near the breakdown region, seven hole probe measurement is less accurate due to a combination of probe interference and flow reversal.
Payne, F. M.↗
A flow visualization and aerodynamic force data evaluation of spanwise blowing on full and half span delta wings
A wind-tunnel investigation has been performed to quantify the effects of a jet on the leading-edge vortices generated by a 70-deg-sweep sharp-edged delta wing at low Reynolds numbers. Efforts were made ot optimize the jet nozzle position with respect to maximum lift increments. Both half-span force-balance testing and half- and full-span flow visualization tests were conducted. Two angles of attack were investigated, 30 and 35 deg, at Reynolds numbers of 150,000 and 200,000. Aerodynamic enhancement, including lift and drag gains of about 20 and 17 percent respectively, were measured. Results indicate an optimum jet nozzle location to be close to the leading edge, tangent to the upper wing surface, and in a direction aligned parallel to the leading edge. Nozzle interference effects, especially near the apex, were not negligible.
Visser, K. D.↗
On leading edge vortex and its control
A simple model for the leading edge vortex and a postulation for the existence of a critical vorticity concentration above which a stable leading edge vortex cannot be maintained were proposed. Using the model and postulation, various aspects of vortex control by blowing were discussed. Blowing can be envisioned as a means to control the effective sweep and span of a delta wing by redistributing the vorticity. Mixing between the blowing jet and the vortex has a major effect on the effectiveness of controlling the vortex. Different positioning of one vortex relative to another can either enhance or delay the breakdown of the vortices.
Ng, T. T.↗
Method of cold smoke generation for vortex core tagging
Attention is given to the flow-visualization problem posed by the 'dark-core' region of the vortices formed on the upper side of a delta wing; the low particle density in the core region minimizes the density of tracing particles whose presence is essential in LDV measurements. An effort is presently undertaken using TiCl4 smoke in subsonic wind tunnel tests of a 70-deg sweep delta wing model.
Nelson, R. C.↗
Visualization and wake surveys of vortical flow over a delta wing
Explore the source record for details and available documents.
Payne, F. M.↗
Control of leading edge vortex breakdown by blowing
An investigation into the effects of using a jet of air to control the vortex breakdown position on a 70 degree delta wing is presented. The specific objectives focused on optimizing the blowing positions in terms of maximum lift increments obtained for minimum blowing rates. The tests were conducted at chord Reynolds numbers of 150,000, 200,000, and 250,000 at angles of incidence of 30 and 35 degrees. Visualization and force data is presented to show the effect of the jet on the wing aerodynamic characteristics. The results indicate a jet position located at and aligned parallel to the leading edge to be the optimum. Nearness to the apex and tangency to the upper surface were also crucial factors. The influence of the jet on the leading edge vortex structure was examined using laser Doppler anemometry. Velocity surveys through the vortex showed that at high blowing rates the parallel velocity in the outer swirling region of the vortex increased and the normal velocity decreased. This resulted in a decrease in the swirling angle in the outer region. The peak core velocity was reduced and the vortex breakdown was delayed.
Visser, K. D.↗
Experimental study of the velocity field on a delta wing
An experimental study of the leading edge vortices on delta wings at large angles of incidence is presented. A combination of flow visualization, seven-hole pressure probe surveys and laser velocimeter measurements were used to study the leading edge vortex formation and breakdown for a set of delta wings. The delta wing models were thin flat plates with sharp leading edges having sweep angles of 70, 75, 80, and 85 degrees. The flow structure was examined for angles of incidence from 10 to 40 degrees and chord Reynolds numbers from 85,000 to 640,000. Vortex breakdown was observed on all the wings tested. Both bubble and spiral modes of breakdown were observed. The visualization and wake survey data shows that when vortex breakdown occurs the core flow transforms abruptly from a jet-like flow to a wake-like flow. The result also revealed that probe induced vortex breakdown was more steady than the natural breakdown.
Payne, F. M.↗
Visualization of vortex breakdown on a delta wing
An account is given of the results obtained by a flow visualization study of the roll-up, breakdown position, and spiral- or bubble-type breakdown characteristics of an 85-deg sweep, flat-plate delta wing at large angles-of-attack. The two different breakdown modes were noted to metamorphose into each other, with the bubble-type phenomenon appearing to prefer a more upstream location relative to the spiral mode. In those instances when the breakdown location was changing, the breakdown took the form of a bubble when moving forward, and spiral when moving aft.
Nelson, R. C.↗
Visualization and flow surveys of the leading edge vortex structure on delta wing planforms
In the present experimental investigation of thin delta wing vortex breakdown, for the cases of sweep angles of 70, 75, 80, and 85 deg, and smoke flow visualization/laser light sheet technique is used to obtain cross sectional views of the leading edge vortices as they break down. A combination of lateral and longitudinal cross sectional views furnishes data on the three-dimensional character of the vortex before, during, and after breakdown. Velocity measurements conducted with a laser Doppler anemometer on the 70 deg sweep delta, at 30 deg angle-of-attack, indicate that when breakdown occurs the core flow is transformed from a jet-like to a wake-like flow.
Payne, F. M.↗
Laser velocimetry measurement in a transonic tunnel
Some preliminary velocity measurements were carried out inside the transonic tunnel using the laser velocimeter (LV) system in association with the smoke generator. Pressure measurements were also performed using a pressure tap located on the side wall of the test section slightly upstream of the windows. Though the pressure measurements and the LV measurements were not taken at exactly the same location, extrapolation of the pressure data into the location of the LV measurements indicated a very close agreement between the velocity values obtained using the two different methods. Thus it is believed that the smoke particle is following the air flow with little or no velocity slip. Velocity measurements with airfoil at various angles of attack are now being carried out in conjuction with schlieren flow visualization. In the near future pressure distribution around and on the airfoil will be obtained by putting pressure taps on the side windows and using a pressure tap model (currently under construction) of the airfoil.
Ng, T. T.↗