1、iiASA Technica I Paper 271 8 July 1987 NASA 2 I Measurements of Flow Rate and Traiectory J - - of Aircraft Tire-Generated Water Spray Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA Tech n ica I Paper 271 8 1987 National Aeronautics and Space Ad
2、ministration Scientific and Technical Information Off ice Measurements of Flow Rate and Trajectory of Aircraft Tire-Generated Water Spray Robert H. Daugherty and Sandy M. Stubbs Langley Research Center Hampton, Virginia Provided by IHSNot for ResaleNo reproduction or networking permitted without lic
3、ense from IHS-,-,-Summary Typically, commercial aircraft certification re- An experimental investigation was conducted at the NASA Langley Research Center to measure the flow rate and trajectory of water spray generated by an aircraft tire operating on a flooded runway. Tests were conducted in the H
4、ydrodynamics Research Fa- cility and made use of a partial airframe and a nose tire from a general aviation aircraft as well as nose tires from a commercial transport aircraft. The ef- fects of forward speed, tire load, and water depth were evaluated by measuring the amount and loca- tion of water c
5、aptured by an array of tubes mounted behind the test tire. Trajectory angles of the side plume emanating from the tire footprint were nearly constant for the range of variables tested. The wa- ter displaced from the path of the tire footprint pro- duced the spray pattern in close proximity to the ti
6、re, while the spray pattern farther aft was primar- ily influenced by the lateral wake produced on the surface of the water by the rolling tire. Increasing forward speed generally increased local water-spray flow rates, and the most concentrated flow in the spray pattern moved inboard slightly. Incr
7、eased tire load decreased the local flow rates of the spray and a larger pattern resulted. Variations in water depth had a more significant effect on the flow rates at posi- tions closer to the tire than at positions farther aft of the t,ire. The effect of a fuselage on the spray pattern was to move
8、 the upper water-flow regions of the spray pattern farther outboard. The addition of a wing generally caused a deflection of the spray downward, but spray was concentrated above the wing by the airflow around it as the wing was moved aft. Com- parisons of spray patterns generated by a bias ply and a
9、 radial tire showed that the two were very sim- ilar in terms of the spray position as well as the flow rates in the pattern. In trod uct ion All aircraft designed to take off and land on con- ventional runways have a requirement to operate dur- ing times when the runway is wet. Many of the effects
10、of wet runways have long been known, such as reduced braking and cornering capability and, on flooded runways, a reduction in takeoff acceleration. The advent of large multiengine aircraft), particu- larly those with aft-fuselage-mounted turbojet en- gines, brought with it the chance of ingesting wa
11、ter spray thrown up by the aircraft tires into the engine intakes. If sufficient water is ingested, a jet engine can experience compressor stalls or even flameout. This stall or flameout situation can be especially dan- gerous if it occurs on the takeoff roll near rotation speed. quires that the air
12、frame manufacturer demonstrate the capability to operate on a runway with one- half inch of standing water without experiencing any spray ingestion problems. Some aircraft have a ge- ometry that is free of spray problems regardless of external conditions such as water depth and speed. Other aircraft
13、 have geometries that make spray in- gestion a common problem that occurs over a wide range of conditions. These are the aircraft that typ- ically must be fitted with chined tires or nosewheel spray deflectors. References 1 and 2 describe some military aircraft that have experienced water-spray inge
14、stion and the associated engine surges or flame- outs. Numerous studies have been conducted to de- termine whether aircraft are susceptible to water- spray ingestion, but they were typically carried out after the aircraft was built. Although the design of aircraft and engine type and location are de
15、pendent on many variables, it is desirable to configure an air- craft and its engines in a geometry that eliminates the spray ingestion potential. The purpose of tliis paper is to present the re- sults of a study conducted at the NASA Langley Research Center to determine the flow rate and tra- jecto
16、ry of water spray generated by an aircraft tire operating on a flooded runway. Tests were conducted in the enclosed Hydrodynamics Research Facility us- ing an electrically driven carriage capable of attain- ing speeds of 80 ft/sec. Effects of parameters, includ- ing water depth, tire load, and forwa
17、rd speed were evaluated by measuring the amount and location of water captured by a fixed array of tubes mounted on the carriage behind the test tire. Tests were con- ducted with the carriage configured in one of three ways: (1) with the nose gear of a twin-engine, general aviation aircraft; (2) wit
18、h the nose gear installed in the aircraft fuselage without a partial wing; and (3) with the nose gear installed in the aircraft fuselage with a partial wing mounted at two fore-and-aft lo- cations. Test were also conducted with the nose tires of larger commercial transport aircraft to determine the
19、effect of radially constructed tires on the gen- erated spray pattern compared with conventionally constructed bias-ply tires. Apparatus Test Facility Tests were conducted in the Hydrodynamics Re- search Facility at the Langley Research Center. The facility consists of a 2900-ft-long enclosed water
20、tank approximately 12 ft deep and 24 ft wide. A schematic of the tank section is shown in figure 1. A set of rails Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-spaced 20 ft apart support an electrically driven car- riage (fig. 2), which can traver
21、se the entire length of the tank. Eight 75-hp motors receive power through a set of electrical trolley wires aid drive eight pneu- matic truck tires, which support the 18-ton carriage. A closed-loop feedback control system allows the car- riage operator to select and maintain a test speed within f0.
22、5 ft/sec. A more detailed description of the facility can be found in reference 3. For this investigation, water was drained from the tank, and a 4-ft-high by 1.5-ft-wide concrete runway 50 ft long was installed in the bottom of the tank with a 20-ft ramp at each end of the runway. The total length
23、was thus 90 ft. The ramps had a 4-in. rise arid were designed to smoothly load and unload the test tire and nose-gear strut, which was restrained vertically by the carriage during a test. Figure 3 is a photograph of the runway. Aluminum pans and side plates were attached along the side of the runway
24、 to provide a total water-trough width of 3 ft. The plates and pan edges were higher than the concrete runway to provide the capability of maintaining a water depth up to 0.6 in. The nose-tire centerline was positioned 27 in. from the right side dam. The runway had adjustable side dams every 5 ft, s
25、o that the desired water depth could be set and maintained by using a water hose to continuously add water to the runway. Test Hardware The test airframe, nose strut, and nosewheel used during this investigation were those from a twin- engine, general aviation aircraft in the 6000-lb class. The nose
26、 tire was a 6.00 x 6, TT, %ply, type I11 air- craft tire with a rated load of 2350 lb and was inflated to 35 psi. The unloaded tire-pressure rating for this tire was 55 psi. Initially, tests were conducted using only the nose gear, mounted on an “I” beam truss as shown in figure 4. The truss was mou
27、nted on the test carriage and was used to position the nose tire on the runway in the bottom of the tank. The upper portion of the strut was restrained vertically, and the vertical load was preset with nitrogen pressure in the strut cylinder prior to a test. Additional tests were conducted to invest
28、igate the effect of aircraft fuselage aerodynamics on the spray pattern. For these tests, the nose gear was mounted in the fuselage, which was installed on the carriage and was restrained with guy wires. Next, a portion of the right wing was attached to the fuselage in order to examine its effect on
29、 the spray patterns. A photograph with the wing installed is shown in figure 5. The wing was later installed at a location farther aft in order to examine the effect of wing position on the spray patterns. Tests were also conducted using a larger conven- tional bias-ply tire and a radial tire to det
30、ermine dif- ferences in the spray patterns due to tire construc- tion. Each tire was a 26 x 6.6 tubeless tire with a ply rating of 12 and a load rating of 8600 lb. An axle was fabricated and the truss shown in figure 4 was modi- fied to permit mounting of these larger tires. Figure 6 is a photograph
31、 of one of these tires installed on the truss. Data Acquisition Since general trends of flow-rate and trajectory data were sought in this investigation, the most straightforward method of capturing the water spray produced by the aircraft tire was utilized. To capture the water, two different collec
32、tors were built. The first collector consisted of an 8- by 8-tube array with 3-in-tube center spacing. Each tube was a clear plastic cylinder with a 1.625-in. inside diameter and with a removable rubber stopper placed in the aft end. Figure 7 is a photograph of the first collector. The collector was
33、 mounted on the carriage behind and to the right of the test tire to sample the water spray generated by the nose tire as it ran through the flooded runway. The collector was slightly tilted with the aft end low, so that the collected water remained in the tubes during carriage deceleration. After t
34、he test, the volume of water collected in each tube was measured to give an indication of the flow rate at that position. No measurable quantity of water adhered to the tube walls after a test. A video camera was mounted to the right and forward of the nose tire but looking aft, and if it showed tha
35、t a complete sampling of the spray was not obtained, the collector was repositioned and the test was repeated to provide a larger area of spray sampling. Often, four or more collector locations were needed to completely define the water-spray pattern at a given distance behind the tire. Later in the
36、 test program, a larger water collector was fabricated with a 22- by 22-tube array with the same spacing as the previous array. The larger collector significantly reduced the time and number of tests required to define the water-spray pattern within a plane and was more accurate because it is diffic
37、ult to duplicate test conditions for successive runs exactly. Figure 8 is a photograph of the larger collector. Additional data were obtained using high-speed movie film in cameras mounted both onboard the moving carriage and along the side of the runway aimed at the test wheel. The movie coverage w
38、as helpful in defining the trajectory of the water spray relative to the ground. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Testing Technique Water Trajectory The test runway used in this investigation was located approximately 1200 ft from on
39、e end of the towing tank to allow sufficient distance for the car- riage to be accelerated to the desired test speed prior to traversing the runway. Prior to each test, water depth was checked and time was allowed for the wa- ter level to return to the selected test depth. Nor- mally, the general av
40、iation nose tire was inflated to 35 psi, and the desired tire load for the test was prese- lected by charging the upper strut to the appropriate pressure. The water collector was positioned for each test run at a selected location on the right side of the nosewheel centerline. The water collector mo
41、unting hardware allowed it to be moved in three directions. One lateral plane aft of the nose gear would nor- mally be surveyed before moving the collector in the fore-and-aft direction. Figure 9 is a sketch of the re- lationship between the tire and the three planes at which the water-spray pattern
42、 was measured. Testing was begun with the carriage operator accelerating the carriage to the desired speed. The nose tire ran up the entrance ramp to load the tire, traversed the flooded runway, and then ran down the exit ramp; then the carriage was slowed to a stop. The water collector sampled the
43、spray pattern during passage through the flooded runway. After the test, the carriage was moved back to the preparation area, and the water that was collected in each tube was measured and recorded. Tests involving the fuselage and wing were conducted in the same manner. Since comparison tests of th
44、e bias-ply and radial commercial transport aircraft nose tires were conducted without a landing gear strut, the axle vertical position relative to the test runway surface was varied to obtain the desired tire deflection. Results and Discussion Table I is a summary of the runs conducted in this inves
45、tigation. The conditions for each run are included along with the coordinates showing the re- lationship between the center of the tire footprint and the lower inboard collector tube face. The“x” coor- dinate denotes the distance aft of the tire footprint center. The “y” and “z” coordinates denote t
46、he dis- tances to the right and upwards, respectively, from the tire footprint center to the lower inboard collec- tor tube face. The water-spray pattern and flow-rate data collected from all the test runs in this study are presented in the appendix. Before discussing the effects of various paramete
47、rs on the spray patterns produced by the aircraft tire operating on a flooded runway, an understanding of the water displacement and spray generation process in and near the tire footprint is needed. As the tire rolls through standing water on a flooded runway, the water in the path of the tire foot
48、print must be almost completely displaced if the tire is operating below the dynamic hydroplaning speed. Some of the water is expelled forward out of the footprint in what is called the “bow wave”. Extensive high-speed film taken of the bow wave showed it to be low in density. Since the bow wave mus
49、t necessarily acquire a forward ground speed greater than that of the tire, the wave atomizes quite rapidly and is perceived to contribute little to the body of water that typically reaches an engine inlet. A “rooster tail”, which consists of a spray directly behind the tire, is also produced. The rooster tail is made up of water expelled from the rear of the footprint or water that clung to the tire surface until it was free of the tire-runway interface. Because of the low q
